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AC. Atomic Structure packet
Name: _________________________________KEY__________________ Date: __________ Period: ______
Atomic Structure
You can become more familiar with the atomic structure of some common substances by completing the chart
below. For each substance, you have been given enough information to fill in all the blanks. Note: Atoms are
neutral
Symbol
Atomic
Mass
Number of
Number of
Number of
Substance
Number
Number
Protons
Neutrons
Electrons
Helium
He
2
4
2
2
2
Magnesium
Mg
12
24
12
12
12
Zinc
Zn
30
65
30
35
30
Bromine
Br
35
80
35
45
35
Aluminum
Al
13
27
13
14
13
Uranium
U
92
238
92
146
92
Sodium
Na
11
23
11
12
11
Krypton
Kr
36
84
36
48
36
Calcium
Ca
20
40
20
20
20
Silver
Ag
47
108
47
61
47
More practice
Atomic
number
1
2
6
20
4
29
8
16
5
11
26
7
13
10
30
50
82
15
35
51
27
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Name of
element
Hydrogen
Helium
Carbon
Calcium
Beryllium
Copper
Oxygen
Sulfur
Boron
Sodium
Iron
Nitrogen
Aluminum
Neon
Zinc
Tin
Lead
Phosphorus
Bromine
Antimony
Cobalt
# of
protons
1
2
6
20
4
29
8
16
5
11
26
7
13
10
30
50
82
15
35
51
27
# of
electrons
1
2
6
20
4
29
8
16
5
11
26
7
13
10
30
50
82
15
35
51
27
# of
neutrons
0
2
6
20
5
35
8
16
6
12
30
7
14
10
35
69
125
16
45
71
32
Atomic mass
(2 decimals)
1.01
4.00
12.01
40.07
9.01
63.55
16.00
32.06
10.81
22.98
55.85
14.00
26.98
20.17
65.39
118.71
207.2
30.97
79.90
121.76
58.93
Mass number
1
4
12
40
9
64
16
32
11
23
56
14
27
20
65
119
207
31
80
122
59
Symbol
H
He
C
Ca
Be
Cu
O
S
B
Na
Fe
N
Al
Ne
Zn
Sn
Pb
P
Br
Sb
Co
AC. Atomic Structure packet
Atomic Structure
An atom is made up of protons and neutrons (Both found in the nucleus) and electrons (in the surrounding
electron cloud). The atomic number is equal to the number of protons. The mass number is equal to the
number of protons plus neutrons. In a neutral atom, the number of protons equals the number of electrons. The
charge on an ion indicates an imbalance between protons and electrons. Too many electrons produces a
negative charge, too few, a positive charge.
This structure can be written as part of a chemical symbol
Example:
Ma
ss
nu
mb
er
15
7
7 protons
8 neutrons (15-7)
4 electrons
Cha
rge
N
Element / Ion
Atomic
number
Ato
mic
nu
mb
Atomic Mass
er
(2 decimals)
H
1
H
12
6
3
Mass number
Protons
Neutrons
Electrons
1.01
1
1
0
1
1
1.01
1
1
0
0
C
6
12.01
12
6
6
6
Li 
3
6.94
7
3
4
2
Cl 
17
35.45
35
17
18
18
39
19
K
19
39.10
39
19
20
19
24
12
Mg 2
12
24.31
24
12
12
10
As 3
33
74.92
75
33
42
36
Ag
47
107.87
108
47
61
47
Ag 1
47
107.87
108
47
61
46
S 2
16
32.07
32
16
16
18
U
92
238.03
238
92
146
92
7
3
35
17
Page 2
AC. Atomic Structure packet
Parts of an atom
An atom is made up of protons and neutrons, which are in the nucleus, and electrons, which are in the electron
cloud surrounding the atom.
The atomic number equals the number of protons. The electrons in a neutral atom equal the number of protons.
The mass number equals the sum of the protons and neutrons.
The charge indicates the number of electrons that have been lost or gained. A positive charge indicates the
number of electrons (which are negatively charged) lost. A negative charge indicates the number of electrons
gained.
This structure can be written as part of a chemical symbol.
Example:
Ma
ss
nu
mb
er
12
6
This carbon ion would have 6 protons, 6 neutrons and 2 electrons.
C
Cha
rge
4
Ato
mic
nu
mb
Complete the following chart.er
Element /
Ion
24
1. 12
Mg
Atomic
number
12
Mass
number
24
Charge
Protons
Neutrons
Electrons
0
12
12
12
2.
39
19
K
19
39
0
19
20
19
3.
Na 1
11
23
+1
11
12
10
4.
23
11
19
9
F 1
9
19
-1
9
10
10
5.
27
13
Al 3
13
27
+3
13
14
10
1
1
0
1
0
1
12
24
+2
12
12
10
47
16
1
108
32
2
0
-2
0
47
16
1
61
16
1
47
18
1
17
35
-1
17
18
18
4
9
+2
4
5
2
6. 11 H
7.
24
Mg 2
8. Ag
2
9. S
10. 12 H
11.
Cl 
35
12. Be 2 
Page 3
AC. Atomic Structure packet
Drawing Atoms
You can draw the structures of some common atoms by knowing their atomic number and number of neutrons.
Using the information below, draw an atom of each substance. Remember to put the correct number of
electrons in each energy level.
Substance
Helium
Lithium
Nitrogen
Fluorine
Neon
Atomic number
2
3
7
9
10
Number of neutrons
2
4
7
10
10
Lithiu
m
Heliu
m
Nitrog
en
e
2
p
-
+
3
p
+
2
n
e
4
n
o
-
o
7
p
+
7
n
o
Fluori
ne
e
Neon
e
-
-
9p+
10
no
Page 4
10
p+
10
no
e
-
AC. Atomic Structure packet
Isotopes
1. a. What are isotopes? Atoms of same element with different mass (different number of neutrons)
b. How are the isotopes of a particular element alike? Same number of protons
c. How are they different? Different number of neutrons
2. Complete the following table relative to the three isotopes of hydrogen.
Isotope
Name
# protons
# electrons
H-1
Protium
1
1
H-2
Deuterium
1
1
H-3
Tritium
1
1
# neutrons
0
1
2
3. a. What is the meaning of the term the atomic number of an element? Number of protons
b. What is the mass number of an isotope? Protons + neutrons
c. In the nuclear symbol for deuterium ( 12 H ) identify the atomic number and the mass number.
Atomic number = 1 Mass number = 2
d. Write its hyphen notation. Hydrogen - 2
4. What is a nuclide? Any isotope of any element
5. Use the periodic table and the information given below to write the hyphen notation for each isotope
described:
a. atomic number = 2, mass number = 4
Helium - 4
b. atomic number = 8, mass number = 16
Oxygen - 16
c. atomic number = 10, mass number = 39
Neon - 39
Label the following as Isotopes or different elements
___Different____ 1. Element D has 6 protons and 7 neutrons. Element F has 7 protons and 7 neutrons.
___Isotope_____ 2. Element J has 27 protons and 32 neutrons. Element L has 27 protons and 33 neutrons.
___Different____ 3. Element X has 17 protons and 18 neutrons. Element Y has 18 protons and 17 neutrons.
___Isotope______ 4. Element Q has 56 protons and 81 neutrons. Element R has 56 protons and 82 neutrons.
___Isotope______ 5. Element T has an atomic number of 20 and an atomic mass of 40. Element Z has an
atomic number of 20 and an atomic mass of 41.
___Different____ 6. Element W has 8 protons and 8 neutrons. Element V has 7 protons and 8 neutrons.
___Isotope_____ 7. Element P has an atomic number of 92 and an atomic mass of 238. Element S has 92
protons and 143 neutrons.
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AC. Atomic Structure packet
Calculating atomic mass
To calculate the atomic mass of an element, _Multiply___________ the mass of each _element_____ by its
natural abundance, expressed as a decimal, and then _add_________ the products
Example:
Isotope 10X
Isotope 11X
Mass = 10.012 amu
Mass = 11.009 amu
Relative abundance = 19.91% = 0.1991
Relative abundance = 80.09% = 0.8009
Atomic mass for X is
[(0.1991) x (10.012 amu)] + [(0.8009)x(11.009 amu)] = ____10.810 amu___________________
Sample isotope atomic mass problems
1. The element Copper has naturally occurring isotopes with mass numbers of 63 and 65. The relative
abundance and atomic masses are 69.2% for mass 62.93 amu and 30.8% for mass 64.93 amu. Calculate the
average atomic mass of copper.
(0.692)(62.93amu) + (0.308)(64.93amu) = 63.546 amu
2. Calculate the atomic mass of Bromine. The two isotopes of bromine have atomic masses and relative
abundance of 78.92 amu (50.69%) and 80.92 amu (49.31%).
(0.5069)(78.92amu) + (0.4931)(80.92amu) = 79.9 amu
3. Magnesium has three naturally occurring isotopes in the following proportions:
Mg – 24 (78.70% , 23.98504 amu) Mg – 25 (10.13%, 24.98584 amu) Mg – 26 (11.17%, 25.9825916 amu)
What is the atomic mass of Magnesium?
(0.7870)(23.98504amu) + (0.1013)(24.98583amu) + (0.1117)(25.9825916amu) = 24.31 amu
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AC. Atomic Structure packet
4. Lithium has 2 isotopes 7.42% of its atoms have a mass of 6.02 amu and 92.58% of its atoms have a mass of
7.02 amu. What is the atomic mass of lithium?
(0.0742)(6.02 amu) + (0.9258)(7.02) = 6.95 amu
5. What is the atomic mass of hafnium if 5% have a mass of 176, 19% have a mass of 177, 27% have a mass
of 178, 14% have a mass of 179, and 35% have a mass of 180?
(0.05)(176 amu) + (0.19)(177 amu) + (0.27)(178 amu) + (0.14)(179 amu) + (0.35)(180 amu) = 179 amu
6. 90% of neon’s atoms have a mass of 20 amu and 10% have a mass of 22 amu. What is neon’s atomic mass?
(0.9)(20 amu) + (0.10)(22 amu) = 20.2 amu
7. Copper exists in nature at copper – 63 atomic mass 62.9298 amu and copper –65 atomic mass 64.9278 amu.
Its atomic weight is 63.546 amu. What must be the approximate abundance in nature of these two isotopes?
(x)(62.9298 amu) + (1-x)(64.9278 = 63.546 amu
62.9298x + 64.9278 – 64.9278x = 63.546
-1.998x = -1.3818
x= 0.691592
So 69.1592% of Cu-63
30.8408% of Cu-65
8. a. What is the relationship between an atom containing 12 protons, 12 neutrons, and 12 electrons and one
containing 12 protons, 13 neutrons, and 12 electrons? Isotopes
b. What is the relationship between an atom containing 12 protons, 12 neutrons, and 12 electrons and one
containing 13 protons, 12 neutrons, and 13 electrons? Different elements
Page 7
AC. Atomic Structure packet
Isotope and average atomic mass
Elements come in a variety of isotopes, meaning they are made up of atoms with the same atomic number
but different atomic masses. These atoms differ in the number of neutrons. The average atomic mass is the
weighted average of all of the isotopes of an element.
Example: A sample of cesium is 75% 133Cs, 20.% 132Cs, and 5% 134Cs. What is the average atomic mass?
Answer: (0.75 x 133 amu) + (0.20 x 132 amu) + (0.05 x 134 amu) = 132.85 amu
Determine the average atomic mass of the following mixtures of isotopes.
1. 80% 127I, 17% 126I, 3% 128I
(0.80)(127) + (0.17)(126) + (0.03)(128) = 126.86 amu
2. 50% 197Au, 50% 198Au
(0.5)(197) + (0.5)(198) = 197.5 amu
3. 15% 55Fe, 85% 56Fe
(0.15)(55) + (0.85)(56) = 55.85 amu
4. 99% 1H, 0.8% 2H, and 0.2% 3H
(0.99)(1) + (0.008)(2) + (0.002)(3) = 1.012 amu
5. 95% 14N, 3% 15N, and 2% 16N
(0.95)(14) + (0.03)(15) + (0.02)(16) = 14.07 amu
6. 98% 12C, 2% 14C
(0.98)(12) + (0.02)(14) = 12.04 amu
Page 8