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Atomic Review
Dissecting Atom
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A:not
Tomos: cutting
What idea about an atom is conveyed from
the meaning of its prefix and suffix?
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Matter can be subdivided only as small as an
atom. An atom cannot be cut or broken down any
further.
Is that true?
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Can an atom be broken down any further?
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Electron
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Proton
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Negatively charged particle outside the nucleus.
Positively charged particle inside the nucleus.
Neutron
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Neutral charged particle inside the nucleus separating
the protons.
Atomic Theories
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Democritus- “atomos” atoms cannot be broken down.
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Dalton-matter is composed of atoms, all atoms of an element are the
same, atoms cannot be created, destroyed, or subdivided, atoms
combine in whole number ratios, atoms are rearranged in chemical
reactions.
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JJ Thomson-electrons are present in atoms mingled with the positive
charges like plums in pudding.
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Rutherford-A positive mass is present in the center of an atom
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Bohr-electrons orbited the nucleus.
Chadwick-discovered neutrons.
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Wave Model-You cannot predict both the whereabouts and the speed
of an electron at one time. Only one can be predicted at a time.
Schrodinger’s wave equation.
The size
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Nucleus
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If the atom was the size of a football field, the
nucleus would be the size of a marble.
A nucleus’ radius is about 0.001 pm.
Very dense!
Atom
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Atomic radii range from 40-270 pm
Number Vocab
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Atomic Number
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Mass Number
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The number of protons in an atom.
Z=
C=6
H=1 O=8
The number of protons and neutrons in an atom.
C=12
H=1 O=16
Isotopes
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Atoms of the SAME element that have different masses.
Protium, Deuterium, Tritium (H-1, H-2, H-3)
Review
Element
Atomic
Number
Atomic
Mass
Protons
Neutrons
Electrons
O
8
15.99
8
8
8
Mg 2+
12
24.31
12
12
10
F-
9
19.00
9
10
10
The atomic # = the number of protons
The mass # of the most common isotope is the atomic mass
rounded to the nearest whole number.
Cations (+) lose electrons.
Anions (-) gain electrons.
Relative Atomic Masses
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The mass of an atom is so small that it has
its own special unit.
AMU
1 amu= 1/12 the mass of a carbon 12 atom.
Therefore a C-12 atom masses 12 amu.
H=1.00794 amu
0=15.9994 amu
We will round the atomic masses to 2
decimal places.
Practice Calculating Average
Atomic Mass
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Copper exists as
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69.15% Cu-63 amu=62.929601
30.85% Cu-65 amu=64.927794
What is the weighted average?
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(62.929601 amu x .6915) + (64.927794 x .3085) =
 63.55 amu (atomic mass units)