Atoms Elements Metals Key Notes by rM4xIRHL

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									                       Atoms, Elements & Metals Key Notes


There are over 100 different elements, arranged in a chart called the periodic
table – the elements are arranged in a special way…


Every element has its own chemical symbol – it is usually one or two letters long
(but can sometimes be three)


Every symbol begins with a capital


The second and third letters are lower case




The vertical columns in the periodic table are called groups – each group contains
elements that have similar properties


The periodic table has eight main groups, e.g. group 1 contains very reactive metals
such as sodium (Na) and potassium (K) whilst group 7 contains very reactive non-
metals such as chlorine (Cl) and bromine (Br)


The horizontal rows are called periods (each new period represents another full
shell of electrons)


The metals are on the left, the non-metals on the right
Atoms have a small central nucleus (containing protons and neutrons) which is
orbited by electrons


All substances are made from atoms, and any given element is made of atoms of
just one particular sort – represented by a specific chemical symbol




The nucleus: -
      In the middle of the atom
      Contains protons and neutrons
      Has a positive (+ve) charge (due to the presence of the protons)
      Almost the whole mass of the atom is concentrated within the nucleus
      Size is tiny compared to the atom as a whole!


The electrons: -
      Orbit the nucleus
      Negatively charged (-ve)
      Tiny, but cover a lot of space
      The volume of their orbits determines how big the atom is
      Virtually no mass
      They occupy shells around the nucleus
Neutral atoms have no overall charge – the size of the charge of the electrons is
the same as that of the protons, just opposite (electrons are –ve and protons are
+ve)


This means in an atom the number of protons equals the number of electrons


*Electrons can be added / removed – if this is done the charged atom is known as
an ion


Periodic table shows one final important piece of information - an element’s atomic
number and it’s atomic mass…


The mass number (top number) shows the number of protons + neutrons


The atomic number (bottom number) shows the number of protons (and therefore,
the number of electrons)




Atoms are extremely small – they are about 0.00000001 cm wide


To make an atom the size of a football it would have to be enlarged ~
3,000,000,000 times


Atoms are so tiny they are measured in nanometres (nm) – they are around 0.1-
0.5nm


The name 'nano' means 10-9 where a nanometre is one millionth of a millimetre (1nm
= 0·000000001 metres)
Atoms consist of a nucleus (containing protons and neutrons) which are orbited by
electrons, within specific shells…


Electrons which orbit the nucleus of an atom occupy specific shells – the follow
some specific rules: -
      Electrons always occupy shells (energy levels)
      The lowest energy levels are always filled up first
      Only a certain number of electrons are allowed in each shell (1st shell = 2; 2nd
       shell = 8; 3rd shell = 8)
      In most atoms the outer shell is not full, making them want to react




Electrons occupying shells around the nucleus is the ‘cause’ of all underlying
chemistry


When elements react their atoms join with other atoms forming compounds – this
involves giving, taking, and sharing of electrons


There is a link between an atom's electronic structure and its position in the
periodic table – an atom's electronic structure can be worked out from its place in
the periodic table…
      Atoms in group I have 1 electron in the out shell
      Atoms in group II have 2 electrons in the outer shell
      Atoms in group III have 3 electrons in the outer shell etc…
      Atoms in group VIII have a full outer shell
Some metals are extremely reactive, whilst others are not – the reactivity series
shows how reactive metals are…




When a metal reacts with water the products are a metal hydroxide and hydrogen
gas…


                  Metal + Water  Metal Hydroxide + Hydrogen


When a metal reacts with oxygen the product is a metal oxide


                          Metal + Oxygen  Metal Oxide


There is a definite pattern between the placement of a metal on the periodic table
and how reactive it is – the most reactive metals are located in groups I and II,
with the least reactive metals being within the transition metals, placed in the
centre of the periodic table, between groups II and III – they are generally hard
and dense, and less reactive than the alkali metals




The electron structure of an atom affects how reactive it is – a shell with just one
electron in is it keen to ‘get rid’ of this so they have a full outer shell


Elements within group I (lithium, sodium, potassium etc…) and group II (magnesium,
calcium, strontium etc…) have just one or two electrons to ‘get rid of’ before they
have a full outer shell, and as such are extremely reactive


The most reactive metals are found within group I and II


Electron structure of an atom affects how reactive it is – a shell with three of
four electrons will find it very difficult to gain / loose enough electrons to have a
full outer shell


Elements within group III and group IV (including the transition metals such as
zinc, silver and gold) have lots of electrons to gain / lose before they have a full
outer shell, and as such as quite un-reactive


This is why metals such as gold can be found as ‘pure’ – they are so un-reactive that
they have not reacted with other chemicals for billions of years
As atoms get bigger they have more full shells of electrons – each new row has one
more full shell


The number of outer electrons is the same for each element within a group


As you go do the group the outer shell of electrons is further from the nucleus –
the inner shells provide shielding from the attraction of the +ve nucleus


As metal atoms get bigger the outer electron is more easily lost – metals are more
reactive as you descend down group I and group II




Atoms can gain a full outer shell (becoming stable) by either gaining or losing
electrons when they react with other atoms


When this reaction occurs atoms become ions


Ions are electrically charged particles, formed when atoms lose or gain electrons –
they have a charge because they contain an unequal number of electrons and
protons…


Atoms which lose electrons have more protons than electrons, and so have a
positive charge – they are known as positive ions or cations


Atoms which gain electrons have more electrons than protons, and so have a
negative charge – they are known as negative ions or anions
Metal atoms lose electrons and become positively charged ions (cations)




Non-metal atoms gain electrons and become negatively charged ions (anions)


The name of an anion is slightly different to that of the atom, ending in ‘–ide’




There is a quick way to work out what the charge on an ion should be: -
      The number of charges on an ion formed by a metal is equal to the group
       number of the metal
      The number of charges on an ion formed by a non-metal is equal to the group
       number minus eight
      Hydrogen forms H+ ions
*Carbon and silicon (group 4) usually form covalent bonds by sharing electrons and
the elements in group 0 do not react


Many power stations burn fossil fuels such as coal and oil, producing smoke


Smoke comprises tiny solid particles, such as carbon which has not reacted, which
can damage buildings and cause breathing difficulties so the smoke is removed
from waste gases before they pass out of the chimneys using an electrostatic
precipitator…




   1. Smoke particles pick up a negative charge
   2. Smoke particles are attracted to the collecting plates
   3. Collecting plates are knocked to remove the smoke particles
Car bodies are given a negative charge and the paint droplets are given a positive
charge


The droplets repel each other so spread out into a fine spray


They are attracted to the oppositely charged car body, producing a smooth even
coat


When metals react with non-metals, electrons are transferred from the metal
atoms to the non-metal atoms, forming ions – the resulting compound is an ionic
compound


Consider reactions between metals and non-metals, e.g.


                        sodium + chlorine → sodium chloride




                      magnesium + oxygen → magnesium oxide
                         calcium + chlorine → calcium chloride




In each of these reactions, the metal atoms give electrons to the non-metal atoms
– the metal atoms become positive ions and the non-metal atoms become negative
ions


A formula uses chemical symbols and numbers to show the ratio of atoms of each
element present in the compound – to work out the formula of an ionic compound
the following needs to take place: -
      Write down the symbol for each atom
      Calculate the charge for each ion
      Balance the number of ions so the positive and negative charges equal zero –
       this gives a ratio of ions
      Write down the formula without the ion charges – the metal is always
       written first
A covalent bond forms when two non-metal atoms share a pair of electrons – the
electrons involved are in the highest occupied energy levels (outer shells) of the
atoms


An atom that shares one or more of its electrons will complete its highest occupied
energy level


Covalent bonds are strong – a lot of energy is needed to break them


Substances with covalent bonds often form molecules with low melting and boiling
points, such as hydrogen and water


Atoms may form multiple covalent bonds – that is, share not just one pair of
electrons but two or more pairs


Atoms of different elements will form either one, two, three or four covalent
bonds with other atoms – there is a quick way to work out how many covalent bonds
an element will form…


The number of covalent bonds is equal to eight minus the group number
Molecules can have a double covalent bonds, meaning they have two shared pairs of
electrons (shown by a double line)


Molecules can also have triple covalent bonds, meaning they have three shared
pairs of electrons (shown by a triple line)


                 Hydrogen atoms can each form one covalent bond
            One pair of electrons is shared in a hydrogen molecule (H2)




                  Oxygen atoms can each form two covalent bonds
   Two pairs of electrons are shared in an oxygen molecule (O2) – a double bond
  Hydrogen atoms can each form one covalent bond, while oxygen atoms can each
                               form two covalent bonds
            Two pairs of electrons are shared in a water molecule (H2O)




  Hydrogen atoms can each form one covalent bond, while and nitrogen atoms can
                            each form three covalent bonds
         Three pairs of electrons are shared in an ammonia molecule (NH3)




There are usually some obvious changes during a chemical reaction, including: -
      A change in colour
      A gas coming off (you may see fizzing or bubbling)
      A change in temperature (the reaction mixture may get hotter)
      A solid may be formed when two solutions are mixed together


New substances are formed by chemical reactions – when elements react together
to form compounds their atoms join to other atoms via chemical bonds


Chemical bonds involve electrons from the reacting atoms – bonds can form when: -
      Electrons are transferred from one atom to another, so that one atom gives
       electrons and the other takes electrons
      Electrons are shared between two atoms


The chemical formula of a compound shows how many of each type of atom join
together to make the units that make the compound up
In iron sulfide every iron atom is joined to one sulfur atom, so we show its formula
as FeS


In sodium oxide, there are two sodium atoms for every oxygen atom, so we show its
formula as Na2O


In carbon dioxide, every carbon atom is joined to two oxygen atoms, so we show its
formula as CO2


When elements are joined to cause a chemical reaction, no atoms are made or lost
during the process - but at the end of it they are joined differently from the way
they were at the start


This means that the mass of the substances at the start (reactants) is the same as
the mass of the substances at the end (products)




There must always be the same number of atoms on both sides – equations are
balanced by putting a number in front of the formulae where needed…


                                   Cu + O2 → CuO


The formulae are all correct but the numbers of some atoms do not match up on
both sides – the formula cannot be changed, only numbers may be added in front of
them
                                 E.g. Copper Oxide


Find an element which does not balance and pencil in a number to try and sort it out
– if this creates another imbalance pencil in another number etc…


                                   Cu + O2 → CuO


In the above equation there are more O atoms on the left than on the right (2O on
the left but only 1O on the right) – to correct this add more O on the right: -


                                  Cu + O2 → 2CuO


This has now caused too many Cu atoms on the right hand side (2Cu on the right
but only 1Cu on the left) – to correct this add more Cu on the left: -


                                  2Cu + O2 → 2CuO


Having changed this we now have a fully balanced equation!


In any reaction the total mass of products is the same as the total mass of the
reactants


The transition metals are found in the large block between groups II and groups
III in the periodic table


Most metals are placed here, including iron, titanium, copper and nickel…
The transition metals have these properties in common: -
      They are metals
      They form coloured compounds
      They are good conductors of heat and electricity
      They can be hammered or bent into shape easily
      They are less reactive than alkali metals
      They have high melting points (but mercury is a liquid at room temperature)
      They are hard and tough
      They have high densities


Aluminium and titanium are two metals with a low density – this means that they
are lightweight for their size


They also have a very thin layer of their oxides on the surface, which stops air and
water getting to the metal, so aluminium and titanium resist corrosion making the
two metals very useful


Aluminium is used for aircraft, trains, overhead power cables, saucepans and
cooking foil


Titanium is used for fighter aircraft, artificial hip joints and pipes in nuclear power
stations


Unlike iron, aluminium and titanium cannot be extracted from their oxides by
reduction with carbon: -
      Aluminium is more reactive than carbon, so the reaction does not work
      Titanium forms titanium carbide with carbon, which makes the metal brittle


Aluminium extraction is expensive because the process needs a lot of electrical
energy


Titanium extraction is expensive because the process involves several stages and a
lot of energy – this especially limits the uses of titanium
Aluminium is extensively recycled because less energy is needed to produce
recycled aluminium than to extract aluminium from its ore


Recycling preserves limited resources and requires less energy, so it causes less
damage to the environment




A rock is a mixture of minerals


A mineral is any solid element or compound formed naturally within the Earth’s
crust


A mineral ore is a mineral which contains enough metal to make it worth while
extracting the metal from (i.e. you’ll make enough money after all the ‘trouble’
needed getting the metal out)!


The more reactive a metal, the harder it is to extract – extracting requires a
chemical reaction to separate the metal (in many cases the metal is found as an
oxide)


Extraction usually involves chemical reduction using carbon or via electrolysis


* Some metals are found as a metal, not an ore, such as gold (although it is very
rare)


The way in which a metal is extracted depends on its reactivity – a more reactive
metal will displace a less reactive metal from its compounds


Carbon (a non-metal) will also displace less reactive metals from their oxides –
carbon is used to extract metals from their ores commercially
Iron is extracted from iron ore in a huge container called a blast furnace (iron ores
such as haematite contain iron oxide)


The oxygen must be removed from the iron oxide to leave the iron behind
(reduction reaction)


Carbon is more reactive than iron, displacing the iron


                      Iron oxide + Carbon → Iron + Carbon dioxide


                              2Fe2O3 + 3C → 4Fe + 3CO2




Metals are extracted from metal ores via: -
      Chemical reduction (using carbon)
      Electrolysis


Metals which are higher than carbon in the reactivity series have to be extracted
using electrolysis: -
    Potassium
    Sodium
    Calcium
    Magnesium
    Aluminium
*Metals below carbon can be extracted via reduction using carbon as it can only
take the oxygen away from the metal oxide if the metal is less reactive than the
carbon itself


Electrolysis is a way to extract reactive metals from their ores, however it is very
expensive as a large amount of electricity is required as well as anodes need
frequent replacement (this is why metals such as aluminium are often recycled as it
is cheaper to sort old metals and re-melt)…


The principle behind it is to turn ions into the atoms required for the following
steps: -
   1. Make the metal ore molten to release the metal ions so they can move
   2. Electrodes cause the metal ions (+ve) to flow to the –ve electrode
   3. At the cathode the ions pick up spare electrons turning from ions into atoms
      where they sink and can be collected


Electrolysis is the process by which ionic substances are decomposed (broken
down) into simpler substances when an electric current is passed through them


For electrolysis to work, the ions must be free to move – ions are free to move
when an ionic substance is dissolved in water or molten


For example, if electricity is passed through copper chloride solution, the copper
chloride is broken down to form copper metal and chlorine gas…
Positively charged ions move to the negative electrode during electrolysis – they
receive electrons and are reduced


Negatively charged ions move to the positive electrode during electrolysis – they
lose electrons and are oxidised


OILRIG – oxidation is loss, reduction is gain



Copper is a good conductor of electricity, and is used extensively to make
electrical wiring and components


The extraction of copper from copper ore is done by reduction with carbon,
however, the copper produced is not pure enough for use as a conductor, so it is
purified using electrolysis


In this process, the positive electrode (anode) is made of the impure copper which
is to be purified. The negative electrode (cathode) is a bar of pure copper. – the
two electrodes are placed in a solution of copper(II) sulfate…


Copper ions leave the anode and are attracted to the cathode, where they are
deposited as copper atoms – the pure copper cathode increases greatly in size,
while the anode dwindles away (he impurities left behind at the anode form a
sludge beneath it)


Electrolysis is very expensive to complete and open cast mines also have a massive
ecological impact. Copper can be also be obtained from copper salts using scrap
iron, however in recent years two new approaches have been made to extract pure
metals: -
   1. Phytomining
   2. Bioleaching
Phytomining uses plants to absorb naturally occurring metal compounds (including
copper) when they grow


Once a significant amount of metal compound has been absorbed the plants are
burned, producing ash which contains the metal compounds


This method can also be used to extract metals from contaminated land


Brassicas (cabbage family) can be used to extract cadmium, cobalt and nickel




Bioleaching uses bacteria to produce leachate solutions that contain metal
compounds…


Some bacteria can live by using the energy of the bonds between sulfur and copper
– in doing so this separates the metal from the ore


Bioleaching is extremely energy efficient, however it is very slow…
Metal theft is increasing in the UK – currently it is the fastest growing theft


This is because metal prices are steadily increasing (with the cost of the raw
materials / oil used for machinery to extract / power electrolysis)


Recycling metals is a way to cheapen their overall cost…


Steel is an alloy – a mixture of two or more elements, where at least one element is
a metal, is called an alloy


The properties of a metal are changed by including other elements, such as carbon


Alloys contain atoms of different sizes, which distort the regular arrangements of
atoms making it more difficult for the layers to slide over each other, so alloys are
harder than the pure metal




In alloys it is more difficult for the layers of atoms to slide over one another


Copper, gold and aluminium are too soft for many uses, but they can be mixed with
other metals to make them harder for everyday use…
      Brass – used in electrical fittings is 70% copper and 30% zinc
      18 carat gold – used in jewellery is 75% gold and 25% copper and other
       metals
      Duralumin – used in aircraft manufacture is 96% aluminium and 4% copper
       and other metals
Smart alloys (shape memory alloy (SMAs)) can return to their original shape after
being bent


They are useful for spectacle frames and dental braces


A metal ore is a mineral (a solid element or compound found naturally in the Earth’s
crust) or minerals which contain enough metal in them to make them economically
viable to mine and extract the metal from them


Minerals and ores are limited – finite resources which will eventually run out…


Metals are extremely useful in a wide range of contexts, and the fact they are
finite means eventually we will run out of them


This makes recycling metals extremely important for the future…


Some common metals and their uses include: -
      Iron – building materials, tools, vehicles and a catalyst in the manufacture of
       ammonia etc…
      Titanium – fighter aircraft, artificial hip joints, pipes in nuclear power
       stations etc…
      Copper – electric cables, water pipes etc…
      Nickel – coins, catalyst in the manufacture of margarine etc…
      Silver and gold – do not corrode in air or water so very useful as jewellery,
       circuit boards and electrical contacts etc…
Quarrying for metals and other materials has huge social, environmental and
economic impacts locally, nationally and internationally


Limestone is a rock that is made mainly of calcium carbonate, CaCO3


Some types of limestone were formed from the remains of tiny animals and plants
that lived in the seas millions of years ago


When it is heated, it breaks down to form calcium oxide and carbon dioxide


Calcium oxide reacts with water to produce calcium hydroxide


Limestone and its products have many uses, including being used to make mortar,
cement, concrete and glass


Metal carbonates such as calcium carbonate break down when heated strongly –
thermal decomposition


                Calcium carbonate → Calcium oxide + Carbon dioxide


                                 CaCO3 → CaO + CO2


The products are a metal oxide (CaO) and carbon dioxide


Metals high up in the reactivity series (e.g. calcium) have carbonates that need a
lot of energy to decompose them whilst metals low down in the reactivity series
(e.g. copper) have carbonates that are easily decomposed


If limestone is heated strongly, it breaks down to form calcium oxide and carbon
dioxide – via a thermal decomposition reaction


Calcium oxide is also called quicklime (yellow when hot, white when cold)
                 Calcium carbonate → Calcium oxide + Carbon dioxide


                                CaCO3 → CaO + CO2


Calcium oxide reacts with water (“slaked”) to form calcium hydroxide, also called
slaked lime
                     Calcium oxide + Water → Calcium hydroxide


                               CaO + H2O → Ca(OH)2


A lot of heat is produced in the reaction




The main uses of limestone and its products are: -
      Limestone (CaCO3) can be used as a building material and in the
       manufacturing of iron
      Glass - heated with sand and soda (sodium carbonate)
      Cement - heated with clay in a kiln
      Concrete - mixed with sand, water and crushed rock
      Mortar - mixed with sand and water
      Quicklime - heated
      Slaked lime (Calcium Hydroxide Ca(OH)2) - mixed with water
      Lime mortar - mixed with water
      Limestone, quicklime and slaked lime are all used to neutralise excess acidity
       in lakes and in soils

								
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