NONMETALS: BENEFITS AND CHALLENGES TO SOCIETY, HEALTH AND THE ENVIRONMENT

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NONMETALS: BENEFITS AND CHALLENGES     TO SOCIETY, HEALTH AND THE ENVIRONMENT Powered By Docstoc
					                                         CONTENTS
Introduction ................................................................................................ 3
A. Hydrogen ................................................................................................ 4
     I. Benefits of Hydrogen ................................................................... 4
    II. Hydrogen new challenges to society ............................................ 4
B. Carbon .................................................................................................... 5
     I. Some beneficial applications of different carbon allotropes and
          isotopes ........................................................................................ 5
              1. Graphite ............................................................................ 5
              2. Carbon blacks ................................................................... 6
              3. Diamond ........................................................................... 6
              4. Charcoals .......................................................................... 6
              5. Fullerenes.......................................................................... 6
              6. Linear acetylenic carbon ................................................... 7
              7. Archaeological Radiochemistry ......................................... 7
    II. Carbon - a basic constituent of many pollutants in the air............. 7
              1. Introducing the major air pollutants ................................... 7
              2. Acid rain ........................................................................... 7
              3. Smog ................................................................................. 8
              4. The Green house effect ..................................................... 8
C. Group VA ............................................................................................... 8
     I. Nitrogen ....................................................................................... 8
              1. Benefits of nitrogen ........................................................... 8
              2. Health effects of nitrogen .................................................. 9
    II. Phosphorus .................................................................................. 10
              1. Phosphorus and our life ..................................................... 10
              2. Phosphorus and pollution .................................................. 10
D. Group VIA ............................................................................................. 10
        I. Benefits of group VIA ............................................................ 10
                    1. Oxygen ........................................................................ 11
                    2. Sulfur ........................................................................... 11
                    3. Selenium ...................................................................... 12
       II. Challenges of group VIA ........................................................ 12
                    1. Oxygen ........................................................................ 12
                    2. Sulfur ........................................................................... 13
                    3. Selenium ...................................................................... 13
E. Halogens ................................................................................................ 13
     I. The benefits of halogens to society, health, and the environment 13
              1. Flourine............................................................................. 13
              2. Chlorine ............................................................................ 15
              3. Bromine ............................................................................ 15
              4. Iodine ................................................................................ 16
    II. The challenges of halogens to society, health, and the
          environment ................................................................................. 16
              1. Flourine............................................................................. 16
                        1.1. Elemental fluorine .............................................. 16



                                                  1
                       1.2. Fluoride ion ........................................................ 16
                       1.3. Hydrogen fluoride and hydrofluoric acid ............ 16
                       1.4. Organofluorines .................................................. 17
             2. Chlorine ............................................................................ 17
             3. Bromine ............................................................................ 18
             4. Iodine ................................................................................ 18
                       4.1. Elemental iodine ................................................. 18
                       4.2. Toxicity of iodide ion ......................................... 18
                       4.3. Iodine sensitivity ................................................ 18
F. Noble gas................................................................................................ 19
   I.    Helium ......................................................................................... 19
         1. Application of Helium ............................................................ 19
         2. Safety of helium ..................................................................... 19
   II.   Neon ............................................................................................ 20
   III.  Argon........................................................................................... 20
         1. Applications of argon ............................................................. 20
         2. Safety of argon ....................................................................... 21
   IV. Krypton ....................................................................................... 21
   V.    Xenon .......................................................................................... 21
         1. Applications of xenon ............................................................. 21
             1.1. Illumination and optics ................................................ 21
                   1.1.1. Gas-discharge lamps ............................................... 21
                   1.1.2. Lasers ..................................................................... 22
             1.2. Medical ........................................................................ 22
                   1.2.1. Anesthesia .............................................................. 22
                   1.2.2. Imaging .................................................................. 23
             1.3. NMR spectroscopy ...................................................... 23
         2. Safety of Xenon ...................................................................... 23
   VI. Radon .......................................................................................... 24
Conclusion .................................................................................................. 25
References .................................................................................................. 26




                                                  2
                                Introduction
   Nonmetals, as their name implies, are elements that display properties
quite different from those of metals. Generally, they are poor conductors of
heat and electricity, and they are not ductile: in other words, they cannot be
easily reshaped. Included in this broad grouping are:
      Hydrogen (H)
      In Group IV: Carbon (C)
      In Group V: Nitrogen (N), Phosphorus (P)
      Several elements in Group VI: Oxygen (O), Sulfur (S), Selenium (Se)
      All elements in Group VII (Except for Astatine) - the halogens
      All elements in Group VII - the noble gases
   Hydrogen has great abundance in the universe and its importance to
chemical studies. Carbon is not nearly as abundant as hydrogen, but it is a
common element of all living things. Two more, addressed in this essay, are
absolutely essential to human life: oxygen and nitrogen. Hydrogen and helium,
a non-metal of the noble gas family, together account for about 99% of the
mass of the universe, while Earth and the human body are composed primarily
of oxygen, with important components of carbon, nitrogen, and hydrogen.
Indeed, much of life-human, animal, and plant - can be summed up with these
four elements, which together make Earth different from any other known
planet.




                                      3
A. Hydrogen

    Hydrogen is the simplest element known - its most common atomic form
contain only one proton and one electron. The atomic form of hydrogen exists
only at very high temperatures, however. Normally, elemental hydrogen is a
diatomic molecule, the product of an exothermic reaction between H atoms:
    H(g) + H(g)→H2(g)
     Hydrogen is the most abundant element in the universe, accounting for
about 70 percent of the universe’s total mass. It is the tenth most elements in
Earth’s crust, where it is found in combination with other elements. Unlike
Jupiter and Saturn, Earth does not have a strong enough gravitational pull to
retain the light-weight H2 molecules, so hydrogen is not found in our
atmosphere.
    Molecular hydrogen is a colourless, odourless, and non-poisonous gas. At
1 atm, liquid hydrogen has boiling point – 252.9oC (20.3 K).

I. Benefits of hydrogen:

    Hydrogen gas plays an important role in industrial processes. About 95
percent of the hydrogen produced is use captively; that is, it is produced at or
near the plant where it is used for industrial processes such as the synthesis of
ammonia.
   The most important compound of hydrogen is water. Unlike other
compound that undergo hydrogen bond, only water can form a three
dimensional network.
     The atmosphere only contains a small amount of water vapor. However
this water vapor plays a major role in keeping the Earth warm.
    Atmospheric gases, including water vapor, are transparent to visible
radiation. As a result, sunlight warms the Earth during the day.

II. Hydrogen new challenges to society:
   The Earth radiates infrared radiation which water can absorb. At night
water acts as a blanket to help prevent thermal energy loss.
    Hydrogen gas can be produced by the reaction between an alkali metal or
an alkaline earth metal (Ca or Ba) and water, but these reactions are too
violent to be suitable for the laboratory preparation of hydrogen gas. Very
pure hydrogen gas can be obtained by the electrolysis of water, but this
method consumes too much energy to be practical on the large scale.
    The economy of hydrogen: the world’s fossil fuel reserves are being
depleted at an alarmingly fast rate. Faces with this dilemma, scientists have
made intensive efforts in recent years to develop a method of obtaining
hydrogen gas as an alternative energy source. Hydrogen gas could replace
gasoline to power automobiles (after considerable modification of the engine,



                                       4
of course) or be used with oxygen gas in these ways is that the reaction are
essentially free of pollutants; the end product formed in a hydrogen-powered
engine or in a fuel cell would be water, just as in the burning of hydrogen gas
in air:
    2H2(g) + O2(g)→ 2H2O(l)
    Of course, success of hydrogen economy would depend on how cheaply
we could produce hydrogen gas and how easily we could store it.
    Although electrolysis of water consumes too much energy for large-
scale application, if scientists can devise a more practical method of ―splitting‖
water molecules, we could obtain vast amount of hydrogen from sea water.
One approach that is currently in the early stage of development would use
solar energy. In this scheme, a catalyst (a complex molecule containing one or
more transition metal atoms, such as ruthenium) absorbs a photon from solar
radiation and becomes energetically excited. In its excited state, the catalyst is
capable of reducing water to molecular hydrogen.

B. Carbon
     Although it constitutes only about 0.09 percent by mass of Earth’s crust,
carbon is an essential element of living matter. Carbon is one of biological
systems elements (O, C, H, P, and S). It is found free in the form of diamond
and graphite, and it is also component of natural gas, petroleum, and coal
(Coal is a natural dark-brown to black solid used as a fuel; it is form from
fossilized plants and consists of amorphous carbon with various organic and
some inorganic compounds).
    Carbon combines with oxygen to form carbon dioxide in the atmosphere
and occurs as carbonate in limestone and chalk.
     Carbon is the best versatile element in forming allotropes. Organized or
unorganized, atom of carbon can take on an incredible number of
arrangements, each different from the other and each forming a different
allotrope. With all their diversity, these substances have one thing in common:
they are made up solely of covalently bonded carbon atoms.

I. Some beneficial applications of different carbon allotropes and isotopes
1. Graphite
     The most familiar form of carbon is graphite.
Mixed with a little clay and formed into a rod, it
becomes the lead in a pencil.
     The arrays of hexagons are arranged in layers
that are loosely held together.                           Figure 1: Graphite, Handbook of
                                                    carbon, graphite, diamond, and fullerenes:
                                                    properties - Bei Hugh O. Pierson- p35




                                        5
2. Carbon blacks
        Carbon black is a material produced by the incomplete combustion of
heavy petroleum products such as coal tar, ethylene cracking tar, and a small
amount from vegetable oil. Carbon black is a form of amorphous carbon that
has a high surface area to volume ratio, although its surface area to volume
ratio is low compared to activated carbon. It is dissimilar to soot because of its
much higher surface area to volume ratio and significantly less (negligible and
non-bioavailable) PAH (polycyclic aromatic hydrocarbon) content. Carbon
black is used as a pigment and reinforcement in rubber and plastic products.
3. Diamond
    Another of allotropes of elemental carbon is diamond. Besides, be blinded
by brilliance of a cut diamond.
    It’s often used on the tips of cutting tools and drills because diamond is
the hardest natural substance. Look at the model of diamond:
    Every carbon atom is attached to four other carbon atoms. Diamond is the
one of the most organized of all substances. In fact, every diamond is one huge
molecule of carbon atoms. This organization of covalently bonded carbons
throughout diamond accounts for its hardness. The organization of carbon
atoms into diamond occurs under extreme pressure and temperature, often at
depths of 200 km and over a long period of time. Diamonds range in the age
from 600 million to 3 billion years old.

4. Charcoals
     Charcoals – the kind you draw with or cook with – are another type of
poorly organized carbon molecules. Charcoals are produced from the burning
organic matter. Some charcoal, called activated charcoal, has much as 1000 m2
of surface area per gram. This property makes activated charcoal useful in
filtering water. Molecules, atoms, and ions responsible for unwanted odors
and tastes in water are attached to and held by the surface of the activated
charcoal as water passed through it in this water-filtering pitcher.

5. Fullerenes
    This is the model of buckminsterfullerene,
C60, which was named after the engineer and
architect Buckminster Fuller, who invented the
geodesic dome shown here. Both the dome and the
molecule are unusually. The molecule of one of a
group of highly organized allotropes of carbon
called fullerenes. According to the model of                  Figure     2:     Fullerenes
                                                        chemistry and reactions - Bei
buckminsterfullerene, architects designed the           Andreas Hirsch, Michael Brettreich
shape of lots of buildings, especially soccer-ball      - p2

shape.




                                        6
6. Linear acetylenic carbon
    This threadlike allotrope of carbon is organized into long spirals of bonded
carbon atoms. Each spiral contains 300 to 500 carbon atoms. It’s produced by
using a laser to zap a graphite rod in a glass container filled with argon gas.
The allotrope splatters on the glass walls and is the removed. Because they
conduct electricity, these carbon filaments may have uses in microelectronics.
Some linear acetylenic carbons may eventually form fullerenes, whereas
others form soot.

7. Archaeological Radiochemistry
    Archaeologists can determine the objects’ age by the carbon-14 method
(In 1946, Willard Libby, working at the University of Chicago, developed the
carbon-14 method for dating objects that contain carbon).
    Carbon-14 is formed in the upper atmosphere. When cosmic rays collide
with atoms in the upper atmosphere, the atoms break up and release subatomic
particles. The carbon-14 is made when a neutron collides with a nitrogen
atom, causing it to lose a proton.
     When the ratio of radioactive carbon-14 to radioactive carbon-12 in a once
living thing is determined and compared with the ratio, must have existed
while the organism was living, the age of the material can be determined. With
the recent development of a device called tandem accelerator mass
spectrometer (TAMS), carbon-14 dating may be more effective.

II. Carbon a basic constituent of many pollutants in the air:
     The air you breathe is literally a matter of life and death. Atmospheric
oxygen is taken into your body and, during respiration, reacts with glucose to
produce the energy required for all the life processes that keep you going.
     Unfortunately, the same air, at times, may contain materials that cause
respiratory diseases and bring about other harmful effects. Air is often polluted
with chemicals produced by human activity. Even Earth itself coughs up some
of the same air pollutants during volcanic eruptions.

1. Introducing the major air pollutants.
    The major chemicals that pollute the air are carbon monoxide, CO; carbon
dioxide, CO2.
     In addition, pollutants form under the influence of sunlight when oxygen,
nitrogen oxides. These reactions produce ozone, O3.

2. Acid rain
    Unpolluted rain is not harmful. However, many industrial and power
plants burn coal and oil. The smoke produced may contain large quantities of
sulfur oxides, suspended particles, and nitrogen oxides. Automobiles also
contribute to the problem by emitting similar oxides. These chemicals react
with water in the air to form acids, such as sulfuric acid. These acids reach the


                                       7
surface of Earth in fog, rain, snow, and dew. Acid rain can have a disastrous
effect when it reaches bodies of water-ways. But if a lake has a high limestone
content, it is able to somewhat neutralize the acid.

3. Smog
     Large cities with many automobiles may have another problem with
airborne pollutants. It is called smog, which is a haze or fog that is made
harmful by chemical fumes and suspended particles it contain.
    Carbon blacks: Carbon blacks make up most of the soot that collects in
chimneys and becomes a fire hazard.

4. The Greenhouse Effect
    During the twentieth century, the great increase in our use of fossil fuels
caused a significant rise in the concentration of carbon dioxide, CO2, in the
atmosphere. Scientists believe that the concentration of atmospheric CO2
could double by early in the 21st century, compared with its level just before
the Industrial Revolution. During the last 100 to 200 years, the CO 2
concentration has increased by 25%.
    Energy from the sun reaches the earth in the form of light. Neither CO2
nor H2O vapor absorbs the visible light in sunlight, so they do not prevent it
from reaching the surface of the earth. The energy given off by the earth in the
form of lower-energy infrared (heat) radiation, however, is readily absorbed
by both CO2 and H2O (as it is by the glass or plastic of greenhouses). Thus,
some of the heat the earth must lose to stay in thermal equilibrium can become
trapped in the atmosphere, causing the temperature to rise. This phenomenon,
called the greenhouse effect, has been the subject of much discussion among
scientists and the topic of many articles in the popular press. The anticipated
rise in average global temperature by the year 2050 due to increased CO 2
concentration is predicted to be 2 to 5°C.
    An increase of 2 to 5°C may not seem like much. However, this is thought
to be enough to cause a dramatic change in climate, transforming now
productive land into desert and altering the habitats of many animals and
plants beyond their ability to adapt.

C. Group VA

I. Nitrogen

1. Benefits of nitrogen
    Better tire pressure retention: nitrogen migrates through a tire 3 to 4 times
slower than oxygen. It may take 6 months to lose 2 psi with nitrogen
compared to less than a month with oxygen.
     Improved fuel economy: a result of having the proper air pressure which
lessens the rolling resistance. Under-inflated tires have a greater rolling
resistance.


                                       8
     Cooler running tires: tires inflated with nitrogen run cooler than tires
inflated with regular air.
    Removal of oxidation: oxygen is a highly reactive element at high
temperatures and pressures. Replacing the oxygen with nitrogen helps
eliminate the oxidation that damages inner liners and belt packages.
     Improved retreadability: eliminating oxidation also improves the
retreadability due to more flexibility in the tire casing. Less tire aging and tire
cord rust could very well increase the number of retreadable casings and also
increase the number of times a casing can be retreaded.
    Elimination of rim rust: since nitrogen is completely dry, condensation is
eliminated which in turn eliminates rim rust.
    On-the-road reliability: tire failures can be significantly reduced which
reduces down time and costly service calls.
    Because of its heavy presence in air, nitrogen is obtained primarily by
cooling air to temperatures below the boiling points of its major components.
Nitrogen boils (that is, turns into a gas) at a lower temperature than oxygen:
−320.44°F (−195.8°C), as opposed to −297.4°F (−183°C). When air is cooled
to −328°F (−200°C) and then allowed to warm slowly, the nitrogen boils first,
and therefore evaporates first. The nitrogen gas is captured, cooled, and
liquefied once more.
     In processing iron or steel, which forms undesirable oxides if exposed to
oxygen, a blanket of nitrogen is applied to prevent this reaction. The same
principle is applied in making computer chips and even in processing foods,
since these items too are detrimentally affected by oxidation. Because it is far
less combustible than air (magnesium is one of the few elements that burns
nitrogen in combustion), nitrogen is also used to clean tanks that have carried
petroleum or other combustible materials.
     As noted, nitrogen combines with hydrogen to form ammonia, used in
fertilizers and cleaning materials. Ammonium nitrate applied primarily as a
fertilizer.

2. Health effects of nitrogen
     Not all nitrogen in the atmosphere is healthful, however. Oxides of
nitrogen, formed in the high temperatures of internal combustion engines, pass
into the air as nitric oxide. This compound reacts readily with oxygen in the
air to form nitrogen dioxide, a toxic reddish-brown gas that adds to the tan
color of smog over major cities.
     Another health concern is posed by sodium nitrate and sodium nitrite,
added to bacon, sausage, hot dogs, ham, bologna and other food products to
inhibit the growth of harmful microorganisms. Many researchers believe that
nitrites impair the ability of a young child's blood to carry oxygen.
Furthermore, nitrites often combine with amines, a form of organic compound,
to create a variety of toxins known as nitrosoamines. Because of concerns


                                        9
about these dangers, scientists and health activists have called for a ban on the
use of nitrites and nitrates as food additives.
    Ammonium nitrate is also a dangerous explosive.

II. Phosphorus

1. Phosphorus and our life
    Phosphorus helps in the processing of vitamins and in the conversion of
food into energy. Phosphorus (P), a nonmetal chemical element, is a needed to
digest protein, calcium compounds, and glucose and helps your body in
processing of vitamins and in the conversion of food into energy.
    These minerals must be present in the body in the correct balance for
optimal health.
     Phosphorus is required by the body for the formation of bone and teeth
     It is needed to digest protein, calcium compounds, and glucose.
     Phosphorus is needed to make ATP (adenosine triphosphate), a major
      source of body energy, and for the breakdowns of sugar (glycolysis).
    It has been found that vitamin D boosts the effectiveness of phosphorus.
    Magnesium helps in the absorption of phosphorus.

    Highly reactive with oxygen, phosphorus is used in the production of
safety matches, smoke bombs, and other incendiary devices. It is also
important in fertilizers, and in various industrial applications. Phosphorus
forms a number of important compounds, most notably phosphates, on which
animals and plants depend.

2. Phosphorus and pollution
    Phosphorus pollution, created by the use of household detergents
containing phosphates, raised environmental concerns in the 1960s and 1970s.
It was feared that high phosphate levels in rivers and creeks would lead to
runaway, detrimental growth of plants and algae near bodies of water, a
condition known as eutrophication. These concerns led to a ban on the use of
phosphates in detergents.

D. Group VIA

I. Benefits of group VIA
    Oxy and sulfur are two typical nonmetal elements in group VIA. They
have an important role not only to human health but also to environment and
society.
   Together with carbon and hydrogen, oxygen accounts for 93% of the
body's mass.




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    Selenium is another element included in group VIA. Although it is toxic in
large doses, selenium is an essential micronutrient for animals.
1. Oxygen
    Oxygen therapy is used to help patients having difficulty breathing. They
are given doses of pure, or nearly pure, oxygen. This is used during surgical
procedures, and to treat patients who have had heart attacks, as well as those
suffering from various infectious or respiratory diseases.
     Oxygen appears in three allotropes (different versions of the same
element, distinguished by molecular structure): monatomic oxygen (O);
diatomic oxygen or O2; and triatomic oxygen (O3), better known as ozone. The
diatomic form dominates the natural world, but in the upper atmosphere,
ozone forms a protective layer that keeps the Sun's harmful ultraviolet
radiation from reaching Earth. Ozone is also mainly used to purify drinking
water, to deodorize air and sewage gases and to bleach waxes, oils and
textiles.
Oxygen is also used in metallurgy, involves refining coke, which is almost
pure carbon, to make carbon monoxide. Carbon monoxide, in turn, reduces
iron oxides to pure metallic iron. Oxygen is also used in blast furnaces to
convert pig iron to steel by removing excess carbon, silicon, and metallic
impurities. In addition, oxygen is applied in torches for welding and cutting. In
the form of liquefied oxygen, oxygen is used in rockets and missiles. The
space shuttle, for instance, carries a huge internal tank containing oxygen and
hydrogen, which, when they react, give the vehicle enormous thrust.
     Oxygen can be used to produce synthetic fuels, as well as for water
purification and sewage treatment. Airplanes carry oxygen supplies in case of
depressurization at high altitudes; in addition, divers carry tanks in which
oxygen is mixed with helium, rather than nitrogen, to prevent the dangerous
condition known as "the bends".
     A strong oxidizing agent, molecular oxygen is one of the most widely
used industrial chemicals. Its main uses are in steel industry and in sewage
treatment. Oxygen is also used as a bleaching for pulp and paper; in breathing
to ease breathing difficulties, in oxyacetylene torches, and as an oxidizing
agent in many organic and inorganic reactions.

2. Sulfur
    Sulfur is a mineral that is present in all cells, especially in cartilage and
keratin of skin and hair. Food containing sulfur, and the need for this mineral
is met when there is an adequate protein in our diet.
   Sulfur is important for a healthy hair, skin and nails, it also helps maintain
oxygen balance for proper brain function.
    Other Function in the body:
    Purify and tone system and promote bile secretion.



                                       11
      Constituent of essential amino-acids.
      It is a mild laxative, thus preventing constipation.
      Helps treat rheumatism, gout and bronchitis.
      Use in the treatment of skin diseases.

3. Selenium

Selenium also plays a role in the functioning of the thyroid gland, by
participating as a cofactor for the three known thyroid hormone deiodinases. It
may inhibit Hashimotos's disease, in which the body's own thyroid cells are
attacked as alien. A reduction of 21% on TPO antibodies was reported with
the dietary intake of 0.2 mg of selenium.
    Selenium is a catalyst in many chemical reactions and is widely used in
various industrial and laboratory syntheses, especially organoselenium
chemistry. It is also widely used in structure determination of proteins and
nucleic acids by X-ray crystallography (incorporation of one or more Se atoms
helps with MAD and SAD phasing.)
    The largest use of selenium worldwide is in glass and ceramic
manufacturing, where it is used to give a red color to glasses, enamels and
glazes as well as to remove color from glass by counteracting the green tint
imparted by ferrous impurities.
    Selenium is used with bismuth in brasses to replace more toxic lead. It is
also used to improve abrasion resistance in vulcanized rubbers.
    Sheets of amorphous selenium convert x-ray images to patterns of charge
in xeroradiography and in solid-state, flat-panel x-ray cameras.
    Selenium is used widely in vitamin preparations and other dietary
supplements, in small doses. Some livestock feeds are fortified with selenium
as well.

II. Challenges of group VIA

1. Oxygen
    The deficiency of oxy is serious now and it has very bad effects on human
health and particular mutation.
     When coal containing sulfur compounds is burned, the consulting sulfur
dioxide and sulfur trioxide can result in atmospheric contamination. The sulfur
oxides from high-temperature combustion are readily dissolved in water
droplets in the atmosphere and returned to the Earth as acid rain. Although the
evidence is still being debated, there seems little doubt that such acid rain has
damaged forests and lakes globally, as well as attacking building materials and
artistic works.
    Oxygen reacts with iron and other metals to form oxides. Many of these
oxides, commonly known as rust, are undesirable.



                                        12
    Every year, millions upon millions of dollars are spent on painting metal
structures, or for other precautions to protect against the formation of metallic
oxides. On the other hand, metallic oxides may be produced deliberately for
applications in materials such as mortar color, to enhance the appearance of a
brick building.

2. Sulfur
    A lot of sulfur in the air can make human feel unpleasant and smell bad.

     Hydrogen sulfide, the best-known hydrogen compound of sulfur, is a
colorless gas that smells like rotten eggs (The odor of rotten eggs actually
comes from hydrogen sulfide, which is formed by the bacterial decomposition
of sulfur-containing proteins). Hydrogen sulfide is a highly toxic substance
that, like hydrogen cyanide, attacks respiratory enzymes

3. Selenium

    Although selenium is an essential trace element, it is toxic if taken in
excess. Selenium poisoning of water systems may result whenever new
agricultural runoff courses through normally dry undeveloped lands.

E. Halogens
     The halogens form Group VII of the periodic table of elements. They are
listed below, along with chemical symbol and atomic number:
    Fluorine (F) 9 Chlorine (Cl): 17 Bromine (Br): 35 Iodine (I): 53
    The halogens all have valence electron configurations of ns2 np5: in other
words, at any energy level n, they have two valence electrons in the s orbital,
and 5 in the p orbital. In terms of phase of matter, the halogens are the most
varied family on the periodic table. Fluorine and chlorine are gases, iodine is a
solid, and bromine (as noted earlier) is one of only two elements existing at
room temperature as a liquid.
    All of the halogens tend to form salts, compounds-formed, along with
water, from the reaction of an acid and base-that bring together a metal and a
nonmetal. Due to this tendency, the first of the family to be isolated-chlorine,
in 1811 - was originally named "halogen," a combination of the Greek words
halos, or salt, and gennan, "to form or generate." In their pure form, halogens
are diatomic, and in contact with other elements, they form ionic bonds, which
are the strongest form of chemical bond. In the process of bonding, they
become negatively charged ions, or anions.

I. The benefits of halogens to society, health, and the environment
1. Fluorine
    Fluorine is a chemical compound that is used in many different ways. It
has several main benefits.



                                       13
    Molecular fluorine can be used in manufacturing. It is used in several
areas such as plasma etching for semiconductor manufacturing as well as flat
panel display models. Fluorine containing compounds are used in light bulbs,
pharmaceuticals, lubricants, and textiles. One of the most important inorganic
fluorides is uranium hexafluoride, UF6, which is essential to the gaseous
diffusion process for separating isotopes of uranium (U-235 and U-238).
Moreover, Fluorocarbons are used in refrigeration and air conditioning. One
chemical property of fluorine is that it creates a very strong bond with other
atoms. This means that all of the products that are created with fluorine in
them are much stronger than products created with different chemical
compounds.
    Another benefit of fluorine is that it can be used to help molten metal
flow. This is actually where the name comes from. It is very useful in
situations where molten metal must not stand still, but cannot move on its
own. Fluorine in a metal working fluid is what helps to create a natural flow of
liquid metal. It allows a person to work with metal easier, because the metal is
able to flow more smoothly.
    Compounds of fluorine can be made in pesticides. This makes it very
useful against household pests such as cockroaches and other bugs.
    Another huge benefit of fluorine has been in the cooking and baking
industry. Fluorine is used to produce polytetrafluoroethylene, a polymer better
known as Teflon which is a component used in non-stick cookware and is a
fluorine based chemical. This is something that is used often on baking
surfaces in order to create a non-stick surface. Therefore, the chemical has
been highly useful in baking and cooking arenas. The companies that use
Teflon on their baking supplies usually see a gain in popularity after they do
so. This is because many people like using Teflon in order to save clean up
time.
    Other benefit of using fluorine is seen in the dental and medical industries.
Fluoride is added to toothpastes in small amount to prevent cavities. Here, it is
very useful because it allows a person to have better dental hygiene. This is
why it has been added so several municipal water supplies. This is a process
that is called water fluoridation. This process allows the teeth strengthening
compounds to be in the water as well.
    Furthermore, the compound is used to create several anesthetics such as
sevoflurane, desflurane, and isoflurane. These are all fluorocarbon
compounds. They are used in general anesthesia.

    Another drug which is made from Fluorine components is Fluconazole.
This is an antifungal drug. It is used to treat and to prevent systemic fungal
infections. Fluorine is also used in a number of drugs to create
fluoroquinolones, which is a family of antibiotics. These are used in a broad-
spectrum way, which means that they treat many different illnesses and
infections. It is also used to treat depression, because it is one of the main
components in several types of antidepressants.


                                       14
2. Chlorine
    Chlorine plays an important biological role in the human body, where the
chlorine ion is the principal anion in intracellular and extracellular fluids.
    Chlorine is an important chemical for water purification. Chlorine in water
is more than three times more effective as a disinfectant against Escherichia
coli than an equivalent concentration of bromine, and is more than six times
more effective than an equivalent concentration of iodine.
    Chlorine was first put to use as bleach, the only way to get stains and
unwanted colors out of textiles or paper was to expose them to sunlight, not
always an effective method. By contrast, chlorine, still used as bleach today,
can be highly effective—a good reason not to use regular old-fashioned bleach
on anything other than white clothing.
    Calcium hydrochloride (CaOCl), both a bleaching powder and a
disinfectant used in swimming pools, combines both the disinfectant and
bleaching properties of chlorine. It is thought that the ClO– ions destroy
bacteria by oxidizing life-sustaining compounds with them. This and the
others discussed here are just some of many, many compounds formed with
the highly reactive element chlorine. Particularly notable—and
controversial—are compounds involving chlorine and carbon.
    Chlorine bonds well with organic substances, or those containing carbon.
In a number of instances, chlorine becomes part of an organic polymer such as
PVC (polyvinyl chloride), used for making synthetic pipe. Chlorine polymers
are also applied in making synthetic rubber, or neoprene. Due to its resistance
to heat, oxidation, and oils, neoprene is used in a number of automobile parts.

3. Bromine
    A wide variety of organobromine compounds are very beneficial.
     First, Brominated flame retardants represent a commodity of growing
importance. If the material burns the flame retardants produce hydrobromic
acid which interferes in the radical chain reaction of the oxidation reaction of
the fire.
    Second, Potassium bromide is used in some photographic developers to
inhibit the formation of fog (undesired reduction of silver).
    Moreover, several dyes, agrichemicals, and pharmaceuticals are
organobromine compounds. Ethidium bromide, EtBr, is used as a DNA stain
in gel electrophoresis.
    A compound containing bromine was widely used by the petroleum
industry as an additive for gasoline containing lead. Ethylene dibromide
(BrCH2CH2Br) reacts with the lead released by gasoline to form lead bromide
(PbBr2), referred to as a "scavenger," because it tends to clean the emissions of
lead-containing gasoline.




                                       15
    Bromine is also used to reduce mercury pollution from coal-fired power
plants. This can be achieved either by treating activated carbon with bromine
or by injecting bromine compounds onto the coal prior to combustion.

4. Iodine
     Among the best-known properties of iodine is its importance in the human
diet. The thyroid gland produces a growth-regulating hormone that contains
iodine, and lack of iodine can cause a goiter, a swelling around the neck. Table
salt does not naturally contain iodine; however, sodium chloride sold in stores
usually contains about 0.01% sodium iodide, added by the manufacturer.
    Iodine, as a heavy element, is quite radio-opaque. Organic compounds of a
certain type (typically iodine-substituted benzene derivatives) are thus used in
medicine as X-ray radio contrast agents for intravenous injection. This is often
in conjunction with advanced X-ray techniques such as angiography and CT
scanning.
    Some radioactive iodine isotopes can be used to treat thyroid cancer. The
body accumulates iodine in the thyroid, thus radioactive iodine can selectively
damage growing thyroid cancer cells while the radioactive dose to the rest of
the body remains small.
    A compound of iodine that deserves mention is silver iodide, AgI. It is a
pale-yellow solid that darkens when exposed to light. In this respect it is
similar to silver bromide. Silver iodide is sometimes used in cloud seeding, a
process for inducing rainfall on a small scale. The advantage of using iodide is
that enormous numbers of nuclei (that is, small particles of silver iodide on
which ice crystals can form) become available. About 1015 nuclei are produced
from 1g of AgI by vaporizing an acetone solution of silver iodide in a hot
flame. The nuclei are then dispersed into the clouds from an airplane.

II. The challenges of halogens to society, health, and the environment
1. Fluorine
1.1. Elemental fluorine
    Elemental fluorine (fluorine gas) is a highly toxic, corrosive oxidant,
which can cause ignition of organic material. Fluorine gas has a characteristic
pungent odour that is detectable in concentrations as low as 20 ppb. As it is so
reactive, all materials of construction must be carefully selected and metal
surfaces must be passivated.

1.2. Fluoride ion
   Fluoride ions are toxic: the lethal dose of sodium fluoride for a 70 kg
human is estimated at 5–10 g.

1.3. Hydrogen fluoride and hydrofluoric acid
    Hydrogen fluoride and hydrofluoric acid are dangerous, far more so than
the related hydrochloric acid, because undissociated molecular HF penetrates


                                       16
the skin and biological membranes, causing deep and painless burns. The free
fluoride, once released from HF in dissociation, also is capable of chelating
calcium ion to the point of causing death by cardiac dysrhythmia. Burns with
areas larger than 25 square inches (160 cm2) have the potential to cause
serious systemic toxicity.

1.4. Organofluorines
    Organofluorines are naturally rare compounds. They can be nontoxic
(perflubron and perfluorodecalin) or highly toxic (perfluoroisobutylene and
fluoroacetic acid). Many pharmacueticals are organofluorines, such as the
anti-cancer fluorouracil. Perfluorooctanesulfonic acid (PFOS) is a persistent
organic pollutant.

2. Chlorine
    Chlorine is a toxic gas that irritates the respiratory system. Because it is
heavier than air, it tends to accumulate at the bottom of poorly ventilated
spaces. Chlorine gas is a strong oxidizer, which may react with flammable
materials.
    Chlorine is detectable in concentrations of as low as 0.2 ppm. Coughing
and vomiting may occur at 30 ppm and lung damage at 60 ppm. About
1000 ppm can be fatal after a few deep breaths of the gas. Breathing lower
concentrations can aggravate the respiratory system, and exposure to the gas
can irritate the eyes.
    Chlorine's toxicity comes from its oxidizing power. When chlorine is
inhaled at concentrations above 30ppm it begins to react with water and cells
which change it into hydrochloric acid (HCl) and hypochlorous acid (HClO).
    When used at specified levels for water disinfection, although chlorine
reaction with water itself usually doesn't represent a major concern for human
health, other materials present in the water can generate disinfection by-
products that can damage human health.
     Chlorofluorocarbons (CFCs), a gas compound of chlorine, have ever been
widely used in fridges. Although it has been banned for a long time, CFCs’
effect in the ozone layer cannot be controlled. Ozone depletion is happening
and widening every day. The protective layer of life on the Earth from harmful
ultra violet light is being destroyed. The ―murderer‖ in CFCs who depletes
ozone layer is exactly chlorine due to followed reactions.
    When CFCs is released and reach the ozone layer under the ultra violet
light, it is decomposed to form atomic chlorine.
                    �������������������� ℎ����
       CF2Cl2 (g)                    CF2Cl(g) + Cl(g)
     Then, atomic chlorine reacts with and depletes ozone according to the
following cycle of reactions:
       Cl(g) + O3 (g) → ClO(g) + O2 (g)



                                                 17
               �������� ������������ℎ����
       O3(g)                    O(g) + O2 (g)
       O(g) + ClO(g) → O2(g) + Cl(g)
    In the final reaction, atomic Chlorine is regenerated and can go through
the cycle again. Through this cycle, a single Chlorofluorocarbon molecule can
deplete thousands of ozone molecules. So, what will we do to treat ozone
depletion of Chlorine in CFCs in order to save life on the Earth?

3. Bromine
    Elemental bromine is toxic and causes burns. As an oxidizing agent, it is
incompatible with most organic and inorganic compounds. Care needs to be
taken when transporting bromine; it is commonly carried in steel tanks lined
with lead, supported by strong metal frames.
     When certain ionic compounds containing bromine are mixed with
potassium permanganate (KMnO4) and an acidic substance, they will form a
pale brown cloud of bromine gas. This gas smells like bleach and is very
irritating to the mucus membranes. Upon exposure, one should move to fresh
air immediately. If symptoms of bromine poisoning arise, medical attention is
needed.

4. Iodine

4.1. Elemental iodine
    Elemental iodine is an oxidizing irritant and direct contact with skin can
cause lesions, so iodine crystals should be handled with care. Solutions with
high elemental iodine concentration such as tincture of iodine are capable of
causing tissue damage if use for cleaning and antisepsis is prolonged.
    Elemental iodine (I2) is poisonous if taken orally in larger amounts;
2-3 grams of it is a lethal dose for an adult human.
    Iodine vapor is very irritating to the eye, to mucous membranes, and in the
respiratory tract. Concentration of iodine in the air should not exceed 1 mg/m³
(eight-hour time-weighted average).
     When mixed with ammonia and water, elemental iodine forms nitrogen
triiodide which is extremely shock sensitive and can explode unexpectedly.

4.2. Toxicity of iodide ion
    Excess iodine has symptoms similar to those of iodine deficiency.
Commonly encountered symptoms are abnormal growth of the thyroid gland
and disorders in functioning and growth of the organism as a whole. Iodides
are similar in toxicity to bromides.

4.3. Iodine sensitivity
    Some people develop sensitivity to iodine. Application of tincture of
iodine can cause a rash. Some cases of reaction to Povidone-iodine (Betadine)


                                                18
have been documented to be a chemical burn. Eating iodine-containing foods
can cause hives. Medical use of iodine (i.e. as a contrast agent, see above) can
cause anaphylactic shock in highly iodine sensitive patients. Some cases of
sensitivity to iodine can be formally classified as iodine allergies. Iodine
sensitivity is rare but has a considerable effect given the extremely widespread
use of iodine-based contrast media.

F. Noble gas
    The noble gases are a group of chemical elements with very similar
properties: under standard conditions, they are all odorless, colorless,
monatomic gases, with a very low chemical reactivity. The six noble gases
that occur naturally are helium (He), neon (Ne), argon (Ar), krypton (Kr),
xenon (Xe), and the radioactive radon (Rn).

I. Helium

1. Application of Helium
    Helium is used for many purposes that require some of its unique
properties, such as its low boiling point, low density, low solubility, high
thermal conductivity, or inertness.
    Because it is lighter than air, airships and balloons are inflated with helium
for lift. While hydrogen gas is approximately 7% more buoyant, helium has
the advantage of being non-flammable. In rocketry, helium is used as an
alleged medium to displace fuel and oxidizers in storage tanks and to condense
hydrogen and oxygen to make rocket fuel. It is also used to purge fuel and
oxidizer from ground support equipment prior to launch and to pre-cool liquid
hydrogen in space vehicles.
    One industrial application for helium is leak detection. Because it diffuses
through solids at three times the rate of air, helium is used as a tracer gas to
detect leaks in high-vacuum equipment and high-pressure containers.
   Second liquid helium is used to cool certain metals to the extremely low
temperatures required for superconductivity, such as in superconducting
magnets for magnetic resonance imaging (MRI).

2. Safety of helium
    Neutral helium at standard conditions is non-toxic, plays no biological role
and is found in trace amounts in human blood. If enough helium is inhaled that
oxygen needed for normal respiration is replaced asphyxia is possible. The
safety issues for cryogenic helium are similar to those of liquid nitrogen; its
extremely low temperatures can result in cold burns and the liquid to gas
expansion ratio can cause explosions if no pressure-relief devices are installed.
    Inhaling helium can be dangerous if done to excess, since helium is a
simple asphyxiant and so displaces oxygen needed for normal respiration.
Breathing pure helium continuously causes death by asphyxiation within
minutes. Inhaling helium directly from pressurized cylinders is extremely


                                        19
dangerous, as the high flow rate can result in barotraumas, fatally rupturing
lung tissue. However, death caused by helium is quite rare.

II. Neon
    Neon is actually abundant on a universal scale: the fifth most abundant
chemical element in the universe by mass, after hydrogen, helium, oxygen,
and carbon .Its relative rarity on Earth, like that of helium, is due to its relative
lightness, high vapor pressure at very low temperatures, and chemical
inertness, all properties which tend to keep it from being trapped in the
condensing gas and dust clouds which resulted in the formation of smaller and
warmer solid planets like Earth.
    The most important application of neon is used to make neon light. Neon
is often used in signs and produces an unmistakable bright reddish-orange
light. Although still referred to as "neon", all other colors are generated with
the other noble gases or by many colors of fluorescent lighting. "Neon" signs
may use neon along with other noble gases.
    Neon is also used in vacuum tubes, high-voltage indicators, lightning
arrestors, wave meter tubes, television tubes, and helium-neon lasers.
Liquefied neon is commercially used as a cryogenic refrigerant in applications
not requiring the lower temperature range attainable with more extreme liquid
helium refrigeration.

III. Argon

1. Applications of argon
   Cylinders containing argon gas for use in extinguishing fire without
damaging server equipment
    There are several different reasons why argon is used in particular
applications:
    An inert gas is needed. In particular, argon is the cheapest alternative
     when diatomic nitrogen is not sufficiently inert.
    Low thermal conductivity is required.
    The electronic properties (ionization and/or the emission spectrum) are
     necessary.
    Other noble gases would probably work as well in most of these
applications, but argon is by far the cheapest. Argon is inexpensive since it is a
by-product of the production of liquid oxygen and liquid nitrogen, both of
which are used on a large industrial scale. The other noble gases (except
helium) are produced this way as well, but argon is the most plentiful since it
has the highest concentration in the atmosphere. The bulk of argon
applications arise simply because it is inert and relatively cheap.




                                         20
2. Safety of argon
     Although argon is non-toxic, it does not satisfy the body's need for oxygen
and is thus an asphyxiant. Argon is 25% more dense than air and is considered
highly dangerous in closed areas. It is also difficult to detect because it is
colorless, odorless, and tasteless. In confined spaces, it is known to result in
death due to asphyxiation. A 1994 incident in Alaska that resulted in one
fatality highlights the dangers of argon tank leakage in confined spaces, and
emphasizes the need for proper use, storage and handling.

IV. Krypton
     Krypton's white discharge is often used to good effect in colored gas
discharge tubes, which are then simply painted or stained in other ways to
allow the desired color. For example, "neon" type advertising signs where the
letters appear in differing colors are often entirely krypton-based. Krypton is
also capable of much higher light power density than neon in the red spectral
line region, and for this reason, red lasers for high-power laser light-shows are
often krypton lasers with mirrors which select out the red spectral line for laser
amplification and emission, rather than the more familiar helium-neon variety,
which could never practically achieve the multi-watt red laser light outputs
needed for this application.
    Krypton has an important role in production and usage of the krypton
fluoride laser. The laser has been important in the nuclear fusion energy
research community in confinement experiments. The laser has high beam
uniformity, short wavelength, and the ability to modify the spot size to track
an imploding pellet.
    Krypton is considered to be a non-toxic asphyxiant. Krypton has a
narcotic potency seven times greater than air, so breathing a gas containing
50% krypton and 50% air would cause narcosis similar to breathing air at four
times atmospheric pressure. This would be comparable to scuba diving at a
depth of 30 m and potentially could affect anyone breathing it. Nevertheless,
that mixture would contain only 10% oxygen and hypoxia would be a greater
concern.

V. Xenon

1. Applications of xenon
   Although xenon is rare and relatively expensive to extract from the Earth's
atmosphere, it still has a number of applications.

1.1. Illumination and optics

1.1.1. Gas-discharge lamps

    Xenon is used in light-emitting devices called xenon flash lamps, which
are used in photographic flashes and stroboscopic lamps; to excite the active
medium in lasers which then generate coherent light; and, occasionally, in


                                        21
bactericidal lamps. The first solid-state laser, invented in 1960, was pumped
by a xenon flash lamp, and lasers used to power inertial confinement fusion
are also pumped by xenon flash lamps.
    Continuous, short-arc, high pressure xenon arc lamps have a color
temperature closely approximating noon sunlight and are used in solar
simulators. That is, the chromaticity of these lamps closely approximates a
heated black body radiator that has a temperature close to that observed from
the Sun. After they were first introduced during the 1940s, these lamps began
replacing the shorter-lived carbon arc lamps in movie projectors. They are
employed in typical 35mm and IMAX film projection systems, automotive
HID headlights and other specialized uses. These arc lamps are an excellent
source of short wavelength ultraviolet radiation and they have intense
emissions in the near infrared, which is used in some night vision systems.
     The individual cells in a plasma display use a mixture of xenon and neon
that is converted into a plasma using electrodes. The interaction of this plasma
with the electrodes generates ultraviolet photons, which then excite the
phosphor coating on the front of the display.

    Xenon is used as a "starter gas" in high pressure sodium lamps. It has the
lowest thermal conductivity and lowest ionization potential of all the non-
radioactive noble gases. As a noble gas, it does not interfere with the chemical
reactions occurring in the operating lamp. The low thermal conductivity
minimizes thermal losses in the lamp while in the operating state, and the low
ionization potential causes the breakdown voltage of the gas to be relatively
low in the cold state, which allows the lamp to be more easily started.

1.1.2. Lasers
     In 1962, a group of researchers at Bell Laboratories discovered laser
action in xenon, and later found that the laser gain was improved by adding
helium to the lasing medium. The first excimer laser used a xenon dimer (Xe2)
energized by a beam of electrons to produce stimulated emission at an
ultraviolet wavelength of 176 nm. Xenon chloride and xenon fluoride have
also been used in excimer lasers.

1.2. Medical

1.2.1. Anesthesia
    Xenon has been used as a general anaesthetic. Although it is expensive,
anesthesia machines that can deliver xenon are about to appear on the
European market, because advances in recovery and recycling of xenon have
made it economically viable. Two mechanisms for xenon anesthesia have been
proposed. The first one involves the inhibition of the calcium ATPase pump -
the mechanism cells use to remove calcium (Ca2+) - in the cell membrane of
synapses. This results from a conformational change when xenon binds to
nonpolar sites inside the protein. The second mechanism focuses on the non-
specific interactions between the anesthetic and the lipid membrane.


                                       22
    Xenon has a minimum alveolar concentration (MAC) of 71%, making it
50% more potent than N2O as an anesthetic. Thus it can be used in
concentrations with oxygen that have a lower risk of hypoxia. Unlike nitrous
oxide (N2O), xenon is not a greenhouse gas and so it is also viewed as
environmentally friendly. In any case, commercial xenon vented to the
atmosphere is simply being returned to its original source, so no
environmental impact is likely.

1.2.2. Imaging
    Gamma emission from the radioisotope 133Xe of xenon can be used to
image the heart, lungs, and brain, for example, by means of single photon
emission computed tomography. 133Xe has also been used to measure blood
flow.
     Xenon, particularly hyperpolarized 129Xe, is a useful contrast agent for
magnetic resonance imaging (MRI). In the gas phase, it can be used to image
empty space such as cavities in a porous sample or alveoli in lungs.
Hyperpolarization renders 129Xe much more detectable via magnetic resonance
imaging and has been used for studies of the lungs and other tissues. It can be
used, for example, to trace the flow of gases within the lungs. Because xenon
is soluble in water and also in hydrophobic solvents, it can be used to image
various soft living tissues.

1.3 NMR spectroscopy
    Because of the atom's large, flexible outer electron shell, the NMR
spectrum changes in response to surrounding conditions, and can therefore be
used as a probe to measure the chemical circumstances around the xenon
atom. For instance xenon dissolved in water, xenon dissolved in hydrophobic
solvent, and xenon associated with certain proteins can be distinguished by
NMR.
     Hyperpolarized xenon can be used by surface-chemists. Normally, it is
difficult to characterize surfaces using NMR, because signals from the surface
of a sample will be overwhelmed by signals from the far-more-numerous
atomic nuclei in the bulk. However, nuclear spins on solid surfaces can be
selectively polarized, by transferring spin polarization to them from
hyperpolarized xenon gas. This makes the surface signals strong enough to
measure, and distinguishes them from bulk signals.
    Besides those, in nuclear energy applications, xenon is used in bubble
chambers, probes, and in other areas where a high molecular weight and inert
nature is desirable. A by-product of nuclear weapon testing is the release of
radioactive Xe-133 and Xe-135.

2. Safety of Xenon
    Many oxygen-containing xenon compounds are toxic due to their strong
oxidative properties, and explosive due to their tendency to break down into



                                      23
elemental xenon plus diatomic oxygen (O2), which contains much stronger
chemical bonds than the xenon compounds.
    Xenon gas can be safely kept in normal sealed glass or metal containers at
standard temperature and pressure. However, it readily dissolves in most
plastics and rubber, and will gradually escape from a container sealed with
such materials. Xenon is non-toxic, although it does dissolve in blood and
belongs to a select group of substances that penetrate the blood-brain barrier,
causing mild to full surgical anesthesia when inhaled in high concentrations
with oxygen.

VI. Radon
     Relative risk of lung cancer mortality by cumulative exposure to radon
decay products (in WLM) from the combined data from 11 cohorts of
underground hard rock miners. Though high exposures (>50 WLM) cause
statistically significant excess cancers, the case of small exposures (10 WLM)
is inconclusive and appears slightly beneficial in this study.
    Although radon exposure has only been conclusively linked to lung
cancer, further studies may be needed to assess the relationship between radon
and leukemia. The effects of radon if ingested are similarly unknown,
although studies have found that its biological half-life ranges from 30–70
minutes, with 90 percent removal at 100 minutes. It has also been shown that
radon progeny can attach itself to the smoke of cigarettes, which then become
lodged within the lungs. It is considered likely that the combination of
smoking and radon exposure increase risk synergistically.
    Radon-222 has been classified by International Agency for Research on
Cancer as being carcinogenic to humans, and as a gas that can be inhaled, lung
cancer is a particular concern for people exposed to high levels of radon for
sustained periods of time. During the 1940s and 50s, safety standards
requiring expensive ventilation in mines were not widely implemented.
     Radon emanation from the soil varies with soil type and with surface
uranium content, so outdoor radon concentrations can be used to track air
masses to a limited degree. This fact has been put to use by some atmospheric
scientists. Because of radon's rapid loss to air and comparatively rapid decay,
radon is used in hydrologic research that studies the interaction between
ground water and streams. Any significant concentration of radon in a stream
is a good indicator that there are local inputs of ground water. Radon is also
used in the dating of oil-containing soils because radon has a high affinity for
oil-like substances.
    Radon soil-concentration has been used in an experimental way to map
buried close-subsurface geological faults because concentrations are generally
higher over the faults. Similarly, it has found some limited use in prospecting
for geothermal gradients. Some researchers have also looked at elevated soil-
gas radon concentrations, or rapid changes in soil or groundwater radon
concentrations, for earthquake prediction. The theory is that compression


                                       24
around a fault about to rupture could produce radon emission, as if the ground
were being squeezed like a sponge
    Radon is a known pollutant emitted from geothermal power stations,
though it disperses rapidly, and no radiological hazard has been demonstrated
in various investigations. The trend in geothermal plants is to reinject all
emissions by pumping deep underground, and this seems likely to ultimately
decrease such radon hazards further.




                                 Conclusion

     Of the 113 known elements, only 17 are nonmetallic elements. Despite
their relative small number, most of the essential elements are nonmetals. As
mentioned, nonmetals are applied in many fields of human life. Besides lots of
their advantages utilized to benefit society, there are still non-understanding
aspects which have not been controlled yet. Although those might be difficult
to human, they are simultaneously new challenges for scientists to study, find
out and solve. Therefore, new uses of nonmetals can be discovered to improve
life quality more and more.




                                      25
                              References
1. Glencoe/McGraw – Hill (2002), Chemistry concepts and applications,
McGraw – Hill Companies, US. p 176-177, 495-755.
2. Raymond Chang (2004), Introduction to chemistry, Singapore, p 882-
886.
3. Shriver D.F. and Atkins P.W. (1992), Inorganic chemistry, Oxford
University Press, US. p 871-879
4. Prentic – Hall, Inc(1994), Atoms Molecules and reactions, A Paramount
communications Company Englewood Cliffs, New Jeigey 07632. p 578.
5. Colin Braird Wendy Gloffke (2003), Chemistry in your life, W.H
Freeman and Company, US. p 55-67
6. Science of Everyday Things.
http://findarticles.com/p/articles/mi_gx5226/is_2002/ai_n19143713/,
Accessed on Mar 24, 2010




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DOCUMENT INFO
Description: Nonmetals, as their name implies, are elements that display properties quite different from those of metals. Generally, they are poor conductors of heat and electricity, and they are not ductile: in other words, they cannot be easily reshaped. Included in this broad grouping are: • Hydrogen (H) • In Group IV: Carbon (C) • In Group V: Nitrogen (N), Phosphorus (P) • Several elements in Group VI: Oxygen (O), Sulfur (S), Selenium (Se) • All elements in Group VII (Except for Astatine) - the halogens • All elements in Group VII - the noble gases Hydrogen has great abundance in the universe and its importance to chemical studies. Carbon is not nearly as abundant as hydrogen, but it is a common element of all living things. Two more, addressed in this essay, are absolutely essential to human life: oxygen and nitrogen. Hydrogen and helium, a non-metal of the noble gas family, together account for about 99% of the mass of the universe, while Earth and the human body are composed primarily of oxygen, with important components of carbon, nitrogen, and hydrogen. Indeed, much of life-human, animal, and plant - can be summed up with these four elements, which together make Earth different from any other known planet.