Chapter 3 – Atoms and Elements

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					Chapter 3 – Atoms and Elements


Section 3.1 – Classification of matter


Matter makes up all physical substances.


Matter has mass and occupies space.


Matter can be separated into pure substances and mixtures.
                                 Elemental substances

             Pure substances

                                         Compounds
 Matter
                                Homogeneous mixtures

                Mixtures

                                     Heterogeneous
                                       mixtures

Pure substances have a fixed or definite composition.
      A pure substance from any source will have the same make up.


A pure substance can be made of:


   1. a single element – an elemental substance, i.e. copper.
   2. a combination of two or more elements – a compound, i.e. water,
      H2O.
An elemental substance consists of only one element.


   Examples: iron, Fe; silver, Ag; neon, Ne.


   Each of these contains only one element.


   Elemental substances can also be polyatomic.


   Example: oxygen, O2




   Would you classify ozone as an elemental substance?
   Ozone is O3.


   Yes, ozone is an elemental substance consisting of only type of
   element.


   What about sulfur, S8?


   Yes, it is also an elemental substance made up of only type of
   element.


A compound defined as a combination of atoms of
two or more elements.


A compound also has a fixed or definite composition.
The ratio of atoms of each element are constant.
         Examples:


         Both water and hydrogen peroxide contain oxygen and
         hydrogen atoms.


         Yet, water and hydrogen peroxide are different compounds.


         Water, H2O, has the same composition irrespective of source.


         Hydrogen peroxide, H2O2, has a different composition than
         water.


         Chemical and physical properties are different for water
         and hydrogen peroxide.


         CuO and Cu2O are different compounds with their own
         unique compostion yet are made from the same two elements.


         A compound can be broken down. Water can be broken
         down into oxygen and hydrogen gas (two elemental
         substances).


            2 H2O  2 H2 + O2




Matter is also found in mixtures that has variable compositions.
Two or more pure substances can be mixed together in varying
amounts.


Air is a mixture of mostly nitrogen and oxygen gases. It is also a
homogeneous mixture.


A mixture can be produced either as a homogeneous mixture
or a heterogeneous mixture.


Homogeneous mixtures have the same composition throughout
and are known as solutions. Examples of solutions include a gas
in a gas, a gas in a liquid, a liquid in a liquid, a solid in a liquid
and a solid in a solid.


Examples: A solution of sugar in water.
             A solution of copper and zinc to form brass, a solution
             known as an alloy.
             14 carat gold is also an alloy.


Heterogeneous mixtures exhibit variable composition from
different portions of the mixture.


Examples: Wood; it has porous structure
             Copper and zinc shavings.
             Blood
             A smoke-filled room
Section 3.2 – Properties of Matter

       Matter and Physical Properties

              Matter defined as having mass and occupying space


              Physical properties of matter

              Ex: melting point, boiling point, density


              States of Matter

                     Solid – has definite shape and volume

                            Ex: ice (water), iron (Fe)

                     Liquid – has definite volume, but not shape

                            Ex: liquid water, mercury (Hg)

                            Shapes of liquids conform to its container

                     Gas – has not definite shape or volume

                            Ex: water vapor

                            Shape and volume are dependent on the shape and
                            volume of the container.



              Physical Change

                     Change of state:                     Solid  liquid

                     Change of appearance:                Dissolve salt in water

                     Change of shape:                     Form a metal, ie. extrude a
                                                          wire

                     Change of size:                      Cut or abrade a metal,
                                                          Change the size of
                                                          container for a gas
Physical States of Water

                  a              b
Solid water (ice) ↔ liquid water ↔ water vapor (gas)

       a: melting (forward)/freezing (back)

       b: boiling (forward)/condensation (back)


Chemical properties describe the ability of a substance
to change into a new substance.


Examples:

       A substance is flammable.

       Wood or paint thinner will burn.

       A substance will corrode.

            Iron exhibits formation of rust (corrosion), with a
            change from a shiny, gray metal to reddish rust
            colored substance.

            Silver will tarnish (corrosion), with a change from
            a shiny, silver metal surface to a black, grainy surface.

       Heating may cause pyrolysis of a substance.

            Sugar will caramelize when heated.


A chemical property such as reactivity covers a wide range of possible
observations – the rate at which the observed reaction occurs.

   A metal such as sodium (Na) reacts with water very vigorously.

   Another metal such as gold (Au) does not react at all with water.
Question 3.7 on page 65
Describe each of the following as physical or chemical properties.

a. Chromium (elemental symbol = Cr) is a steel-gray metal.
   Answer: This is a physical property – the color of the substance.
b. Hydrogen (chemical formula = H 2) reacts readily with oxygen (O 2).
   Answer: This is a chemical property that describes the chemical
   reactivity of hydrogen.
c. Nitrogen (N2) freezes at -210 oC.
   Answer: This is a physical property – a change of state with nitrogen
   going from a liquid to a solid.
d. Milk will sour when left in a warm room.
   Answer: This is a chemical property where substances in milk are
   converted into new chemicals as the milk sours.

Question 3.9 on page 65
What type of change, physical or chemical, takes place in each of the
following? (Note: In this question, I have given you the atomic symbols of
elements to begin getting you familiar with them.)

a. Water vapor condenses to form rain. Answer: This is a physical change
   – the water vapor changes state from gas to liquid.
b. Cesium metal (Cs) reacts explosively with water (H 2O). Answer: This is
   a chemical change – cesium reacts with water to form new chemical
   substances.
c. Gold (Au) melts at 1064 oC. Answer: This is a physical change – gold
   undergoes a change of state when it goes from a solid to a liquid.
d. A puzzle is cut into 1000 pieces. Answer: This is a physical change – an
   object is cut into many pieces.
e. Sugar dissolves in water. Answer: This is a physical change – sugar is
   dissolved into water with no change into a new chemical substance.

Question 3.11 on page 65
Describe each property of the element fluorine (F) as physical or chemical.

a. highly reactive Answer: Chemical property that describes fluorine as a
   reactive chemical.
b. is a gas at room temperature Answer: Physical property that describes
   the physical state of fluorine at room temperature.
c. has a pale, yellow color Answer: Physical property that describes the
   color of the substance.
d. will explode in the presence of hydrogen Answer: Chemical property
   that describes the reactivity with hydrogen.
e. has a melting point of -220 oC Answer: Physical property that describes
   the temperature where the change of state occurs when fluorine solid is
   melted and forms a liquid.
Section 3.3 – Temperature (See Chapter 2.9 in First Ed.)
Temperature is a measure of how much energy is stored in an object
that is the result of heat energy.


Heat energy is related to the movement of atoms and molecules.


The hotter an object, the greater/faster an object will move.


Heat energy will always move from a hotter object to a colder one.


Temperature scales have been devised to measure the amount of
heat energy that an object or system contains.


The Celsius and Fahrenheit scales are examples of two scales in
common use.


The Celsius and Fahrenheit scales were set up with the freezing and
boiling point of water as reference points.


Another scale is the Kelvin scale.
The Kelvin scale is set up with absolute zero at 0 K.


Figure 2.13 on page 58 shows the relationships between these three
scales.
Equalities can be written with these relationships.
The temperature difference between the freezing point and the boiling
point of water is divided into 180 Fahrenheit degrees on the Fahrenheit
scale and 100 Celsius degrees on the Celsius scale.


The temperature differences on the two scales can be expressed
as an equality: 180 Fahrenheit degrees = 100 Celsius degrees.


180 Fahrenheit degrees = 1.8oF
100 Celsius degrees         1oC


Because the Fahrenheit and Celsius scales are offset by 32 oF,
32 has to be added when converting oC to oF and subtracted
when converting oF to oC.


The equation is: TF = 1.8oF (TC) + 32o
                       1oC

or    TF = 1.8(TC) + 32o

The use of a decimal number in the above equation shows the
current usage of electronic devises to conduct calculations.


Example: If today’s expected high temperature is 31 oC convert it to oF.


You can follow the same steps previously used to solve problems.


Step 1:           Given 31oC         Need TF with the unit oF
Step 2:              Plan – use the temperature equation.


Step 3:              Equality/Conversion factor
             TF = 1.8oF (TC) + 32o


Step 4:      Set up Problem
             TF = 1.8oF (31) + 32o
             TF = 88oF


To convert from Fahrenheit degrees to degrees Celsius,
rearrange the equation, TF = 1.8(TC) + 32o, to convert
degrees Fahrenheit to degrees Celsius.


TF - 32o = 1.8(TC) + 32o - 32o


TF - 32o = 1.8(TC)               now divide both sides by 1.8

(TF - 32o) = 1.8(TC)             or
  1.8        1.8

Tc = (TF - 32o)
       1.8



If the actual high for today is 91 oF and you want to tell your friend
in Germany how warm it was today, what would the temperature be
on the Celsius scale?
Step 1:            Given 91oF          Need temperature as oC


Step 2:            Plan – use the temperature equation


Step 3:            Equality/conversion factor – rearrange to solve for oC


      Use the temperature equation after rearranging to solve for T C.


      Tc = (TF - 32o)
             1.8

Step 4:            Set up problem
      Tc = (TF - 32o) = (91oF - 32o)
             1.8            1.8

      Tc = 33 oC




A second equality relates the Celsius to Kelvin scales.
As before, the temperature differences between the freezing point and
boiling point of water is given be the equality:


100 Celsius degrees = 100 Kelvin degrees or
1 Celsius degree = 1 Kelvin degree


Because the two scales are offset by 273 degrees,
      TK = TC + 273             or rearranged
      TC = TK - 273
Example: Because you are conducting an experiment involving a gas,
you need the temperature of the gas in degrees Kelvin. Since the lab
is not air-conditioned, the temperature is 91 oF.
What is the Kelvin temperature?


Step 1:     Given 91oF                Need degrees Kelvin


Step 2:     Plan: Convert oF to oC with the temperature equation
            and then convert to K with a Celsius to K equation.


Step 3:     Equalities/Conversion factors


      Tc = (TF - 32o)    and TK = TC + 273
             1.8

Step 4:     Set up problem.
            91oF was converted to 33 oC.
            See the set up previously used.
            Now use the second equation to solve for K.


            TK = TC + 273 = 33oC + 273
            TK = 306 K


Section 3.4 Energy (See Chapter 9.1 in First Ed.)
      Energy – defined as the ability to do work

      Potential energy – stored energy

      Kinetic energy – energy of motion
       Heat energy – associated with the motion of a chemical substance

       The SI unit “joule” is used to describe the heat energy content

       Calorie (cal) is an older unit – 1 cal is heat energy required to
       raise 1 gram of water 1 degree Celsius.

       1 cal = 4.184 J

       A Calorie (capitalized) is used for food – 1 Cal = 1000 cal

       Examples Problem 3.27 on page 76




Section 3.5 – Specific Heat

       Specific heat – physical property of matter

       Each chemical substance has a unique specific heat value

       Specific heat – the amount of heat energy required to raise the temperature
       of 1-g of a substance 1 degree Celsius

       Specific heat = SH = heat (q)/(grams x ∆T) or SH = q/(mass x ∆T)

              Where ∆T is change in temperature in Celsius
              and mass is in grams

       Specific heat values for selected substances are given on Table 3.7 page 76

       Keep track of change in temperature - will let you know if heat is lost or
       gained

				
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