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STRUCTURE OF THE ATOM ~~ NOTES
PAGE:__________
More Notes about the atom block on the Periodic Table…
Finding Protons:
 The same as the atomic #
a. Atomic # (A) is the element’s # on the periodic table (PT)
b. All atoms of the same element have the same atomic #, regardless of its mass.
 Ex: Na is #11 on the PT & has 11 protons
Finding Neutrons:
 Subtract the atomic # (Z) from the mass # (A)
a. Mass # = # protons + # neutrons
b. Mass # (A) can be found by rounding the atomic mass (from the PT) to the nearest whole number.
c. IF you are given an isotope, the mass # is in the name.
d. IF you are given a nuclear symbol, the top # is the mass #
a. Ex: Mg (#12) has an atomic mass of 24.3. The mass # is 24 (rounded atomic mass). The # of
protons is 12 (because it’s #12). The number of neutrons = 24 – 12 = 12.
Finding Electrons:
a. Electrons = protons IF the atom doesn’t have a charge (i.e. it’s not an ion; no oxidation # is shown)
i. Ex: F has 9 p+ , so it has 9 eb. Cation: protons > electrons by the # given as a superscript (number on the top right with a positive
charge)
i. Ex: Be+2 has 2 fewer electrons than protons; Be+2 = 2 electrons
c. Anion: electrons > protons by the # given as a superscript (number on the top right with a negative
charge)
i. Ex: F-1 has 1 more e- than p+; F-1 = 10 eNuclear Symbols (These are also called IONS):
A
-/+
Shows mass # (A), atomic # (Z), and ionic charge (cation or anion)
Z X
32
-3
 Mass # is on top left:
15P
 Atomic # is on bottom left:
Mass # = 32
p+ = 15
e- = 18
0
 Ionic Charge is on top right:
Atomic # = 15
n = 17
 How do you name these? Start with the element. Then the A number. In parentheses put either cation/anion
and the value). So 3215P-3 would be: Phosphorus-32 (anion -3)
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Isotopes:
Different forms of the same element that have different mass #s because they have different # of neutrons.
 Writing Isotope names: Write the name of the element & indicate the mass with the name.
a. Ex: Carbon-12
C-12 has a mass # of 12 & therefore 6 neutrons
b. Ex: Carbon-14
C-14 has a mass # of 12 & therefore 8 neutrons
Both have 6 protons (because it’s C)
ISOTOPE PRACTICE: Hint: Check your notes about isotopes and protons and electrons!
Element
Nuclear
Symbol
15
N
Atomic
Number
Mass
Number
#
#
#
Protons Neutrons Electrons
7
8
45
Uranium- 238
92
He
5
36
146
2
5
Lithium – 7
184
W
184
79
54
Magnesium – 24
12
55
6
Mn
ION PRACTICE: Hint: Check your notes about ions or nuclear symbols!
Element
Nuclear Atomic
Cation
#
#
#
Symbol
Mass
or
Protons Electrons Neutrons
Anion?
Magnesium27 (cation +2)
Anion
9
10
60
Charge
on Ion
Co+2
Uranium-235
(cation +2)
19
18
30
28
13
10
Gold-108
(cation +1)
Cation
+3