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Atomic Structure
Components of the Atom
Parts of the Atom
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Proton and Neutron
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Both found in the nucleus
Denoted p+ and no
Protons have a positive charge while
neutrons are neutral.
Electrons
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Found in outer orbitals (e-)
Have a negative charge
General Atomic Structure
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Atom Information
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Atomic Number (Z): Number assigned
to each atom denoting the number of
protons (Hydrogen is 1 and has 1
proton)
Atomic Mass Number (A): Number of
protons and neutrons in an atom.
Atomic Notation
Displaying the atomic number
and mass number at the same
time.
  A = neutrons + protons
  Z = protons
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Mass Number (A) = p+ + n0
23
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Na
Element Symbol
Atomic Number (Z) = # of
protons
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Atomic Variations
# of protons determines element.
Isotope: atoms of the same element
having different masses.
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Example
12
13
6
6
C
C
Two isotopes of carbon
Atomic Variations
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Ion: atoms of the same element having
different charges.
Cation: ion with a positive charge
Anion: ion with a negative charge
Examples::
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Atomic Mass Unit
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AMU:: 1 amu = 1/12 of the mass of a
C-12 atom.
It is related to the value on the periodic
table.
Is an older unit and not part of SI
The mole is SI unit.
Molar Masses

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The value on the periodic table is the
mass of one mole of that element.
1 mole = 6.022 x 1023 of anything

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The number of particles in 12g of
carbon-12 atoms that are unbound.
Atoms, molecules, compounds.
Nobel Prize awarded in 1926.
Definition accepted in 1980.
How much do atoms weigh??
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Take a look at your friend the periodic
table.
What do you notice about the masses?
Many atoms have multiple isotopes.
This must be accounted for so mass
measurements are consistent.
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Same atom, different mass??
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Remember isotopes…atoms (identified
by number of protons) can have
differing numbers of neutrons.
Any atomic sample contains multiple
isotopes of that atom….
For example…
Average Atomic Masses
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There are 7 different naturally occurring
isotopes of chromium.
They vary in atomic mass number from
50 to 63.
The mass of each isotope is taken into
consideration when calculating average
atomic mass.
Chromium Isotopes
52Cr = 83.8%
Cr = 4.3%
53Cr = 9.5%
54Cr = 2.4 %
61-63
Trace amounts:
Cr
  50
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Using the mass from any one of these
would not represent a sample found in
nature.
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Determining Average Masses
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Weighted Averages are used to find
average masses.
63Cu 69.17%
62.92 amu
65Cu 30.83%
64.92 amu
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