Atomic Structure and the Periodic Table

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Chapter 5

• Atomic Structure and the Periodic Table

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Section 5.1Atoms

• OBJECTIVES
• Summarize Daltons atomic theory.

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Section 5.1Atoms

• OBJECTIVES
• Describe the size of an atom.

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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.

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History of Atom

• Smallest possible piece?
• Atomos - not to be cut

• Looked at beach
• Made of sand
• Cut sand - smaller sand

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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

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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.

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Whos Next?

• Late 1700s - John Dalton- England.
• Teacher- summarized results of his experiments
  and those of others.
• Daltons Atomic Theory
• Combined ideas of elements with that of atoms.

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Daltons 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.

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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

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Section 5.2Structure of the Nuclear Atom

• OBJECTIVES
• Distinguish among protons, electrons, and
  neutrons in terms of relative mass and charge.

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Section 5.2Structure 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.

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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.

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Thomsons Experiment

-
Vacuum tube
Metal Disks
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Thomsons Experiment

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Thomsons Experiment

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Thomsons Experiment

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Thomsons Experiment

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• Passing an electric current makes a beam appear
  to move from the negative to the positive end

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Thomsons Experiment

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• Passing an electric current makes a beam appear
  to move from the negative to the positive end

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Thomsons Experiment

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• Passing an electric current makes a beam appear
  to move from the negative to the positive end

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Thomsons Experiment

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• Passing an electric current makes a beam appear
  to move from the negative to the positive end

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Thomsons Experiment

• By adding an electric field

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Thomsons Experiment

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• By adding an electric field

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Thomsons Experiment

-

• By adding an electric field

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Thomsons Experiment

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• By adding an electric field

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Thomsons Experiment

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• By adding an electric field

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Thomsons Experiment

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• By adding an electric field

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Thomsons Experiment

-

• By adding an electric field he found that the
  moving pieces were negative

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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?

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Rutherfords 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.

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Rutherfords experiment

• When an alpha particle hits a fluorescent screen,
  it glows.
• Heres what it looked like (page 111)

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Fluorescent Screen
Lead block
Uranium
Gold Foil
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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.

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What he expected
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Because
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He thought the mass was evenly distributed in the
atom
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Since he thought the mass was evenly distributed
in the atom
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What he got
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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.

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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.

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Subatomic particles p.111
Actual mass (g)
Relative mass
Name
Symbol
Charge
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
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Section 5.3Distinguishing Between Atoms

• OBJECTIVES
• Explain how the atomic number identifies an
  element.

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Section 5.3Distinguishing Between Atoms

• OBJECTIVES
• Use the atomic number and mass number of an
  element to find the numbers of protons,
  electrons, and neutrons.

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Section 5.3Distinguishing Between Atoms

• OBJECTIVES
• Explain how isotopes differ, and why the atomic
  masses of elements are not whole numbers.

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Section 5.3Distinguishing Between Atoms

• OBJECTIVES
• Calculate the average atomic mass of an element
  from isotope data.

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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

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Symbols

• Contain the symbol of the element, the mass
  number and the atomic number.

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Symbols

• Contain the symbol of the element, the mass
  number and the atomic number.

Mass number
X
Atomic number
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Symbols

• Find the
• number of protons
• number of neutrons
• number of electrons
• Atomic number
• Mass Number

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F
9
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Symbols

• Find the
• number of protons
• number of neutrons
• number of electrons
• Atomic number
• Mass Number

80
Br
35
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Symbols

• if an 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

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Symbols

• if an element has 91 protons and 140 neutrons
  what is the
• Atomic number
• Mass number
• number of electrons
• Complete symbol

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Symbols

• if an element has 78 electrons and 117 neutrons
  what is the
• Atomic number
• Mass number
• number of protons
• Complete symbol

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Isotopes

• Dalton was wrong.
• Atoms of the same element can have different
  numbers of neutrons.
• different mass numbers.
• called isotopes.

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Naming Isotopes

• We can also put the mass number after the name of
  the element.
• carbon- 12
• carbon -14
• uranium-235

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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.
• Dont use grams because the numbers would be too
  small.

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Measuring Atomic Mass

• Unit is 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.

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Calculating averages

• Multiply the atomic mass of each isotope by its
  abundance (expressed as a decimal), then add the
  results.
• Sample 5-5, p.120

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Atomic Mass

• Calculate the atomic mass of copper if copper has
  two isotopes. 69.1 has a mass of 62.93 amu and
  the rest has a mass of 64.93 amu.

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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

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Atomic Mass

• Is not a whole number because it is an average.
• are the decimal numbers on the periodic table.

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Section 5.4The Periodic Table Organizing the
Elements

• OBJECTIVES
• Describe the origin of the periodic table.

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Section 5.4The Periodic Table Organizing the
Elements

• OBJECTIVES
• Identify the position of groups, periods, and the
  transition metals in the periodic table.

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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

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Mendeleev

• Left blanks for undiscovered elements
• When discovered, good prediction
• Problems?
• Co and Ni Ar and K Te and I

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New way

• Henry Moseley British physicist
• Arranged elements according to increasing atomic
  number
• The arrangement today
• P.124 long form
• Symbol, atomic number mass

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Periodic table

• Horizontal rows periods
• There are 7 periods
• Periodic law
• Vertical column group (or family)
• Similar physical chemical prop.
• Identified by number letter

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Areas of the periodic table

• Group A elements representative elements
  1,2,13-18
• Wide range of phys chem prop.
• Metals electrical conductors, have luster,
  ductile, malleable

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Metals

• Group 1 IA alkali metals
• Group 2 2A alkaline earth metals
• Transition metals and Inner transition metals
  Group B 3-12
• All metals are solids at room temperature, except
  _____.

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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 17 7A halogens
• Group 18 8A noble gases

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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