Chapter 5 by VDH4ZBs

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									       Chapter 5




Atomic Structure and the
     Periodic Table
 Charles Page High School
   Dr. Stephen L. Cotton
          Section 5.1
            Atoms
 OBJECTIVES:
 –Summarize Dalton’s atomic
  theory.
           Section 5.1
             Atoms
 OBJECTIVES:
 –Describe the size of an atom.
         History of the atom
 Not the history of atom, but the idea of
  the atom.
 Original idea Ancient Greece (400
  B.C.)
 Democritus and Leucippus- Greek
  philosophers.
           History of Atom
 Looked at beach    Smallest
 Made of sand       possible piece?
 Cut sand - smaller Atomos - not to
  sand               be cut
              Another Greek
 Aristotle  - Famous philosopher
 All substances are made of 4
  elements
 Fire - Hot
 Air - light
 Earth - cool, heavy
 Water - wet
 Blend these in different proportions to
  get all substances
         Who Was Right?
 Greek society was slave based.
 Beneath famous to work with hands.
 Did not experiment.
 Greeks settled disagreements by
  argument.
 Aristotle was more famous.
 He won.
 His ideas carried through middle
  ages.
 Alchemists change lead to gold.
           Who’s Next?
 Late  1700’s - John Dalton-
  England.
 Teacher- summarized results of his
  experiments and those of others.
 Dalton’s Atomic Theory
 Combined ideas of elements with
  that of atoms.
     Dalton’s Atomic Theory
 All matter is made of tiny indivisible
  particles called atoms.
 Atoms of the same element are
  identical, those of different atoms are
  different.
 Atoms of different elements combine in
  whole number ratios to form
  compounds.
 Chemical reactions involve the
  rearrangement of atoms. No new
  atoms are created or destroyed.
   Just How Small Is an Atom?
 Think  of cutting a piece of lead into
  smaller and smaller pieces
 How far can it be cut?
 An atom is the smallest particle of
  an element that retains the
  properties of that element
 Atoms-very small: Fig. 5.2, p. 108
  –still observable with proper
    instruments: Fig. 5.3, page 108
           Section 5.2
 Structure of the Nuclear Atom
 OBJECTIVES:
 –Distinguish among protons,
  electrons, and neutrons in terms
  of relative mass and charge.
           Section 5.2
 Structure of the Nuclear Atom
 OBJECTIVES:
 –Describe the structure of an
  atom, including the location of the
  protons, electrons, and neutrons
  with respect to the nucleus.
           Parts of Atoms
 J.  J. Thomson - English physicist.
  1897
 Made a piece of equipment called
  a cathode ray tube.
 It is a vacuum tube - all the air has
  been pumped out.
    Thomson’s Experiment
         Voltage source
-                         +


         Vacuum tube

         Metal Disks
    Thomson’s Experiment
         Voltage source
-                         +
    Thomson’s Experiment
         Voltage source
-                         +
    Thomson’s Experiment
         Voltage source
-                         +
       Thomson’s Experiment
             Voltage source
   -                             +

 Passingan electric current makes a
 beam appear to move from the
 negative to the positive end
       Thomson’s Experiment
             Voltage source
   -                             +

 Passingan electric current makes a
 beam appear to move from the
 negative to the positive end
       Thomson’s Experiment
             Voltage source
   -                             +

 Passingan electric current makes a
 beam appear to move from the
 negative to the positive end
       Thomson’s Experiment
             Voltage source
   -                             +

 Passingan electric current makes a
 beam appear to move from the
 negative to the positive end
       Thomson’s Experiment
               Voltage source




 By   adding an electric field
        Thomson’s Experiment
                Voltage source

                        +



                        -
 By   adding an electric field
        Thomson’s Experiment
                Voltage source

                        +



                        -
 By   adding an electric field
        Thomson’s Experiment
                Voltage source

                        +



                        -
 By   adding an electric field
        Thomson’s Experiment
                Voltage source

                        +



                        -
 By   adding an electric field
        Thomson’s Experiment
                Voltage source

                        +



                        -
 By   adding an electric field
       Thomson’s Experiment
             Voltage source

                     +



                     -
 By adding an electric field he found
 that the moving pieces were negative
           Other particles
 Proton - positively charged pieces
  1840 times heavier than the
  electron – by E. Goldstein
 Neutron - no charge but the same
  mass as a proton – by J. Chadwick
 Where are the pieces?
     Rutherford’s experiment
 Ernest Rutherford -English physicist.
  (1910)
 Believed in the plum pudding model of
  the atom (discussed in Chapter 13).
 Wanted to see how big they are.
 Used radioactivity.
 Alpha particles - positively charged
  pieces- helium atoms minus electrons
 Shot them at gold foil which can be made
  a few atoms thick.
     Rutherford’s experiment
 When an alpha particle hits a
  fluorescent screen, it glows.
 Here’s what it looked like (page 111)
                      Fluorescent
Lead    Uranium          Screen
block

                  Gold Foil
           He Expected
 The  alpha particles to pass through
  without changing direction very
  much.
 Because…?
 …the positive charges were
  thought to be spread out evenly.
  Alone they were not enough to stop
  the alpha particles.
What he expected
Because
He thought the mass was evenly
distributed in the atom
Since he thought the
mass was evenly
distributed in the atom
What he got
How he explained it
 Atom is mostly empty.
 Small dense,
  positive piece
  at center.              +
 Alpha particles
  are deflected by
  it if they get close
  enough.
+
      Density and the Atom
 Since most of the particles went
  through, it was mostly empty space.
 Because the pieces turned so much,
  the positive pieces were heavy.
 Small volume, big mass, big density.
 This small dense positive area is the
  nucleus.
   Subatomic particles – p.111
                  Relative Actual
Name Symbol Charge mass    mass (g)
Electron   e-   -1   1/1840 9.11 x 10-28

Proton     p+   +1     1    1.67 x 10-24

Neutron    n0   0      1    1.67 x 10-24
           Section 5.3
 Distinguishing Between Atoms
 OBJECTIVES:
 –Explain how the atomic number
  identifies an element.
           Section 5.3
 Distinguishing Between Atoms
 OBJECTIVES:
 –Use the atomic number and mass
  number of an element to find the
  numbers of protons, electrons,
  and neutrons.
           Section 5.3
 Distinguishing Between Atoms
 OBJECTIVES:
 –Explain how isotopes differ, and
  why the atomic masses of
  elements are not whole numbers.
           Section 5.3
 Distinguishing Between Atoms
 OBJECTIVES:
 –Calculate the average atomic
  mass of an element from isotope
  data.
        Counting the Pieces
 Atomic  Number = number of
  protons in the nucleus
 # of protons determines kind of
  atom (since all protons are alike!)
 the same as the number of
  electrons in the neutral atom.
 Mass Number = the number of
  protons + neutrons.
 These account for most of mass
            Symbols
 Containthe symbol of the element,
 the mass number and the atomic
 number.
              Symbols
 Containthe symbol of the element,
 the mass number and the atomic
 number.
           Mass
          number

            Atomic
            number
                     X
            Symbols
 Findthe
  –number of protons
  –number of
   neutrons            19
  –number of            9   F
   electrons
  –Atomic number
  –Mass Number
            Symbols
 Findthe
  –number of protons
  –number of neutrons
                         80
  –number of electrons
                         35   Br
  –Atomic number
  –Mass Number
            Symbols
 ifan element has an atomic
  number of 34 and a mass number
  of 78 what is the
  –number of protons
  –number of neutrons
  –number of electrons
  –Complete symbol
            Symbols
   an element has 91 protons and
 if
  140 neutrons what is the
  –Atomic number
  –Mass number
  –number of electrons
  –Complete symbol
             Symbols
 ifan element has 78 electrons and
  117 neutrons what is the
   –Atomic number
   –Mass number
   –number of protons
   –Complete symbol
              Isotopes
 Dalton  was wrong.
 Atoms of the same element can
  have different numbers of neutrons.
 different mass numbers.
 called isotopes.
        Naming Isotopes
 We  can also put the mass number
  after the name of the element.
 carbon- 12
 carbon -14
 uranium-235
            Atomic Mass
 How  heavy is an atom of oxygen?
   –There are different kinds of oxygen
    atoms.
 More concerned with average atomic
  mass.
 Based on abundance of each element
  in nature.
 Don’t use grams because the numbers
  would be too small.
     Measuring Atomic Mass
 Unitis the Atomic Mass Unit (amu)
 One twelfth the mass of a carbon-
  12 atom.
 Each isotope has its own atomic
  mass, thus we determine the
  average from percent abundance.
         Calculating averages
 Multiplythe atomic mass of each
  isotope by it’s abundance (expressed
  as a decimal), then add the results.
 Sample 5-5, p.120
              Atomic Mass
          the atomic mass of copper if
 Calculate
 copper has two isotopes. 69.1% has a
 mass of 62.93 amu and the rest has a
 mass of 64.93 amu.
            Atomic Mass
 Magnesium     has three isotopes.
  78.99% magnesium 24 with a mass of
  23.9850 amu, 10.00% magnesium 25
  with a mass of 24.9858 amu, and the
  rest magnesium 25 with a mass of
  25.9826 amu. What is the atomic mass
  of magnesium?
 If not told otherwise, the mass of the
  isotope is the mass number in amu
           Atomic Mass
 Isnot a whole number because it is
  an average.
 are the decimal numbers on the
  periodic table.
          Section 5.4
The Periodic Table: Organizing
         the Elements
 OBJECTIVES:
 –Describe the origin of the periodic
  table.
          Section 5.4
The Periodic Table: Organizing
         the Elements
 OBJECTIVES:
 –Identify the position of groups,
  periods, and the transition metals
  in the periodic table.
   Development of the Periodic
            Table
 mid-1800s,   about 70 elements
 Dmitri Mendeleev – Russian
  chemist
 Arranged elements in order of
  increasing atomic mass
 Thus, the first “Periodic Table”
           Mendeleev

 Leftblanks for undiscovered
  elements
 When discovered, good prediction
 Problems?
  –Co and Ni; Ar and K; Te and I
             New way

 Henry Moseley – British physicist
 Arranged elements according to
  increasing atomic number
 The arrangement today
 P.124 – long form
 Symbol, atomic number & mass
           Periodic table

 Horizontal rows = periods
  –There are 7 periods
 Periodic law:
 Vertical column = group (or family)
  –Similar physical & chemical prop.
  –Identified by number & letter
   Areas of the periodic table

 GroupA elements = representative
 elements
 –Wide range of phys & chem prop.
 –Metals: electrical conductors,
   have luster, ductile, malleable
              Metals

 Group   IA – alkali metals
 Group 2A – alkaline earth metals
 Transition metals and Inner
  transition metals – Group B
 All metals are solids at room
  temperature, except _____.
             Nonmetals

 Nonmetals:    generally nonlustrous,
  poor conductors of electricity
  –Some gases (O, N, Cl); some are
    brittle solids (S); one is a fuming
    dark red liquid (Br)
 Group 7A – halogens
 Group 0 – noble gases
    Division between metal &
            nonmetal
 Heavy,  stair-step line
 Metalloids border the line
   –Properties intermediate between
    metals and nonmetals
 Learn the general behavior and
  trends of the elements, instead of
  memorizing each element property

								
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