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Atomic Structure
Basic Structure
n=4
n=3
n=2
n=1
Energy
levels = n
Nucleus: contains
Protons (p+) and
neutrons (n0)
Subatomic Particles: p+, e-, n0
p+ and n0
have equal
mass
e- smallest
mass
P+ = positive
e- = negative
N0 = neutral
Charge
Calculating the number of electrons in
an energy level. 2n2
n=1
2(1)2 = 2e-
n=2
2(2)2 = 8e-
n=3
2(3)2 = 18e-
n=4
2(4)2 = 32e-
Bohr Model of the atom
Atomic Number = Number
of p+ in the nucleus and
the total number of e-
79
Au
196.967
14
W
14-protons
14-electrons
C
25 – protons
25 – electrons
55.7
80
H
201.5
0
C
Neutral
0
H
30.25
25
0
W
Equal numbers
of p+ and emeans that
atoms are
neutral
80 – protons
80 – electrons
Element
C
K
Atomic number
6
19
p+
6
19
e6
19
Cu
Ag
O
Na
29
47
8
11
29
47
8
11
29
47
8
11
He
Li
Ca
2
3
2
3
2
3
20
20
20
Relative mass or Mass number
79
Au
196
79
Au
197
Mass number = 196 amu
How many p+
How many eHow many n0
79
79
117
Mass # = p+ + n0
196 = 79 + n0
n= 117
Mass number = 197 amu
How many p+
79
How many e-
79
118
How many n0
Mass # = p+ + n0
197 = 79 + n0
n= 118
Element
H-2
Helium - 5
Al - 27
Calcium - 41
U - 238
Oxygen - 17
I - 127
Neon - 21
Sc-46
Nuclear
Symbol
Number
of
Protons
Number of
Neutrons
Number of
Electrons
Avg.
Atomic
Mass
Mass
Number
Atomic
Number
Element
Number of
Protons
H +1
Helium - 5
Al +3
Ca +2
1
U0
O-2
I -1
Ne0
S -2
2
13
20
Number of
Electrons
Atomic
Number
Nuclear
or
Hyphen
notation
1
H11
2
2
He52
10
13
0
18
20
Al2713
Ca4020
Cation
or
Anion
Or
Atom
Cation
atom
Cation
Cation
92
92
92
8
10
8
O168
Anion
53
54
53
I12753
Anion
10
16
U23892
atom
10
10
Ne2010
atom
18
16
S3216
Anion
Average atomic mass (amu)
79
Au
196.967
Note: this is an average.
Atoms of the same
elements are different
sizes.
What are these called?
Isotopes
Protons + Neutrons
Comparison of Isotopes
Atomic mass is the average of all the naturally
isotopes of that element. Carbon = 12.011
Isotope
Symbol Composition of % in nature
the nucleus
12C
Carbon-12
6 protons
98.89%
6 neutrons
Carbon-13
13C
6 protons
7 neutrons
1.11%
Carbon-14
14C
6 protons
8 neutrons
<0.01%
Atomic mass unit = (amu)
 12C
atom = 1.992 × 10-23 g

atomic mass unit (amu)

1 amu = 1/12 the mass of a 12C atom

1 p = 1.007276 amu
1 n = 1.008665 amu
1 e- = 0.0005486 amu
© Addison-Wesley Publishing Company, Inc.
Average Atomic Mass

weighted average of all isotopes on the Periodic
Table
Avg.
Atomic
Mass
(mass)(% )  (mass )(% )

100
D. Average Atomic Mass

EX: Calculate the avg. atomic mass of oxygen if its
abundance in nature is 99.76% 16O, 0.04% 17O, and
0.20% 18O.
Avg.
(16)(99.76 )  (17)(0.04)  (18)(0.20)
 16.00
Atomic 
100
amu
Mass
D. Average Atomic Mass

EX: Calculate the avg. atomic mass of oxygen if its
abundance in nature is 55.32% 25X, 0.94% 23X, and
43.74% 24X.
Avg.
(25)(55.32 )  (23)(0.94)  (24)(43.74 ) 24.54

Atomic
100
amu
Mass
D. Average Atomic Mass

EX: Calculate the avg. atomic mass of oxygen if its
abundance in nature is 99.97% 1H, 0.02% 2H, and
0.01% 3H.
Avg.
Atomic
Mass
(1)(99.97)  (2)(0.02)  (3)(0.01)


100
16.00
amu
Average Atomic Mass

EX: Calculate the avg. atomic mass of oxygen if its
abundance in nature is 50% 197Au, 50% 198Au.
Avg.
Atomic
Mass
(197)(50)+ (198)(50)

 197.5 amu
100
Average Atomic Mass

EX: Calculate the avg. atomic mass of oxygen if its
abundance in nature is 80% 127I, 17% 126I, and 3%
128I.
Avg.
(127)(80 )  (126)(17)  (128)(3)
Atomic 
100
Mass
 126.86
amu
Average Atomic Mass

EX: Find chlorine’s average atomic mass if
approximately 8 of every 10 atoms are chlorine-35
and 2 are chlorine-37.
Avg.
Atomic
Mass
(35)(8)  (37)(2)

 35.40 amu
10
Average Atomic Mass

EX: Find element Y’s average atomic mass if
approximately 5 of every 10 atoms are Y- 64 and 2
are Y- 61and 3 are Y - 60
Avg.
Atomic 
Mass
(5)(64)  (61)(2)  (3)(60)

10
62.2
amu
A
1000
B
Jb
U
17
N
D
A
1000
1000
1000
N
Jb
Jb
Jb
10
20
30
50%
30%
C
E
20%
Take out
of
percent
1000
Calculating
Move
decimal
2 places
two the
Average
Atomic
left
50
%
0.5 X 10 =
5 amu
0.3 X 20 =
6amu
1000
Jb
30
%
20
1000
Jb
30
Mass
D
D
Jb
10
A
20
%
0.2 X 30 =
+ 6 amu
17 amu
E
A
C
H
N
U
M
B
E
R
A
1
B
H
U
1.0979
N
D
Protium
A
1
N
H
C
E
Note the average with a decimal
Deuterium
Tritium
1
1
H
H
1
2
3
98.985%
0.997%
Note the whole numbers
0.001%
Take out
of
percent
1
Calculating
Move
decimal
2 places
two the
Average
Atomic
left
A
Mass
D
H
1
98.985 %
0.98985 X 1 = 0.98985 amu
0.997
0.00997X 2 = 0.01994 amu
1
H
%
2
1
H
3
D
0.001 %
0.00001 X 3 = + 0.00003 amu
1.0982 amu
E
A
C
H
N
U
M
B
E
R
A
14
B
Si
U
28.1088
N
Note the average with a decimal
D
A
14
N
Si
C
E
14
14
Si
Si
28
29
30
92.21%
4.70%
Note the whole numbers
3.09%
Take out
of
percent
14
Calculating
Move
decimal
2 places
two the
Average
Atomic
left
A
Mass
D
Si
28
92.21
%
0.9221 X 28 = 25.8188 amu
14
Si
4.70
%
0.047X 29 =
1.363 amu
29
14
Si
30
D
3.09
%
0.0309 X 30 = + 0.927 amu
28.1088 amu
E
A
C
H
N
U
M
B
E
R
What period is H
located in?
Drawing Atoms
P=1
What group is H in?
1
N=0.0979
H
Mass # = p+ + n0
1.0979 = 1 + n0
0.0979 = n0
1.0979
What period is Ne
located in?
Drawing atoms
What group is Ne
in?
10
P=10
N=10
Mass # = p+ + n0
20 = 10 + n0
10 = n0
Ne
20
What period is B
located in?
Drawing atoms
What group is B in?
5
P=5
N=6
Mass # = p+ + n0
11 = 5 + n0
6 = n0
B
11
What period is Na
located in?
Drawing atoms
What group is Na
in?
11
P=11
N=12
Mass # = p+ + n0
22 = 11 + n0
11 = n0
Na
22
What period is Cl located
in?
Drawing atoms
What group is Cl in?
17
P=17
N=18
Mass # = p+ + n0
Mass # = 17 + 18
35 = n0
Cl
35
Draw the Bohr structure of atoms 1-20
odd
Label the protons, neutrons and electrons
What group is it in?
What period is it in?
Cations: positive ions
Oxidation:
Loss of e-
atom
Na 0
Mg 0
ion
Na+1
Mg+2
Usually metals
form cations
+ e+ 2 e-
Cation
Anions: negative ions
Reduction
is gain of e-
atom
ion
S 0 + 2eN 0 + 3e-
S-2
N-3
Usually nonmetals
form anions
Beryllium – atomic #: 4, # of n: 5
Sodium – atomic #: 11, # of n: 123.
Sulfur – atomic #: 16, # of n: 164.
Fluorine – atomic #: 9, # of n: 10 5.
Calcium – atomic #: 20, # of n: 206.
Argon – Atomic #: 18, # of n: 22
Draw the Bohr structure of atoms 1-20
odd
Label the protons, neutrons and electrons
What group is it in?
What period is it in?
The Octet Rule
Click here



The octet rule states that atoms are most stable
when they have a full shell of 8 electrons in the
outside electron shell. Octet = 8
An atom with eight electrons in the outer shell is
more stable than an atom which has fewer
electrons in the outer shell.
The exception to this is Helium (atomic number 2)
which only has two electrons in its outer shell. It has
a full shell, so it is a stable inert element.
Group number and oxidation states
What do I do with
this electron to
become and ion?
e
What to do?
How will I ever
get to 8e- in my
outter energy
What are
level.
8e2e-
By using the
my
group choices?
number
gain or
on theLose,
periodic
share.
table
I have
octet if
IWill
am
noanlonger
I lose an e-?
Yes Because
the I
neutral
because
2nd energy level
lost an e-??????
Yes!!!!
Li
How
already has 8e-
Does this happen
with all metals like
me?
What charge am
I now?
I’d say Spastic
Atom
I am happy
atom
Group number and oxidation states
Octet Rule or Rule of 8
Predicting Ionic Charges
Group 1: Lose 1 electron to form 1+ ions
H+
Li+ Na+
K+
Predicting Ionic Charges
Group 2: Loses 2 electrons to form 2+ ions
Be2+
Mg2+
Ca2+
Sr2+
Ba2+
Predicting Ionic Charges
B3+
Al3+
Ga3+
Group 13: Loses 3
electrons to form
3+ ions
Predicting Ionic Charges
Neither! Group 13
elements rarely form
ions.
Group 14: Lose 4
electrons or gain
4 electrons?
Predicting Ionic Charges
N3- Nitride
P3- Phosphide
As3- Arsenide
Group 15: Gains 3
electrons to form
3- ions
Predicting Ionic Charges
O2- Oxide
S2- Sulfide
Se2- Selenide
Group 16: Gains 2
electrons to form
2- ions
Predicting Ionic Charges
F1- Fluoride
Br1- Bromide
Cl1-Chloride
I1- Iodide
Group 17: Gains 1
electron to form
1- ions
Predicting Ionic Charges
Group 18: Stable
Noble gases do not
form ions!
Models of Atoms
Dalton Model
click here
A solid, indivisible sphere
John Dalton
click here
Click here
Dalton's Atomic Theory





All matter is made of atoms
·An atom is indivisible.
Atoms of the same element are identical.
Atoms of different elements are different.
Atoms are rearranged to produce new
substances. Atoms combine in whole number
ratios.
Thomson Model
click here (Plum – Pudding Model)
Atom no longer considered indivisible
Electrons are randomly
dispersed in a positive pudding
JJ .Thomson
click here
Click here
Mass of the Electron click here
1909 – Robert Millikan
determines the mass of
the electron.
The oil drop apparatus
Mass of the
electron is
9.109 x 10-31 kg
Rutherford Model
The positive is no longer all
over the atom – it is
concentrated in the center at
the nucleus
The electrons are randomly
dispersed outside of the nucleus
The nucleus is very small
in respect to the atom and
contains virtually all of the
atom’s mass
Rutherford’s experiment click here
Simulation
Try it Yourself!
In the following pictures, there is a target hidden by
a cloud. To figure out the shape of the target, we
shot some beams into the cloud and recorded where
the beams came out.
Can you figure out the shape of the target?
The Answers
Target #1
Target #2
Bohr Model of the Atom
Click here: Science Trek: Wave
particle theory
Click here How things work: atoms
Wave Model –
Electron Cloud Model