Chemistry 4.0
Unit 3: Atomic Theory Homework Packet
Name_
ANSWER KEY____________
Isotopes
1) Distinguish between:
a. atomic number and mass number
Atomic Number is the number of Protons (always), the Mass Number is the number of
Protons + the number of Neutrons. Mass Number accounts for the entire atom’s mass.
b. atomic mass and mass number
Atomic Mass is an average of all the masses of all isotopes of an element; Mass Number is
the mass of one isotope of an element.
2) An isotope is found to have 7 protons and 7 neutrons. What is its
c. atomic number
b. mass number
c. isotopic symbol
7
14
7
14
3) Circle the symbols that are isotopes of one another.
24
12
52
6
a.
X b.
X c.
X d.
X
12
6
24
3
e.
24
X
11
f.
N
23
X
11
4) Write the isotope name for each symbol in question 10.
a. _Magnesium-24_____________
b. __Carbon-12_________________
c. __Chromium-52 _____________
d. __Lithium-6_________________
e. ___Sodium-24 _______________
f. ___Sodium-23________________
5) Write the isotopic symbols for atoms with the following:
55
19
25 Mn
9F
a. 9 p+ and 10 no ________________
b. 25 p+ and 30 no________________
+
o
c. 31 p and 39 n
70
31
________________
Ga
1
1
d. 1 p and 0 n __________________
+
o
H
6) A certain isotope of cobalt is five times as heavy as carbon -12. Write the name and symbol for this
isotope.
60
27 Co
____Cobalt-60___________________
________________
7) In each of the following, information on two elements are provided. Given that information, indicate if
the two elements are isotopes of one another.
a. One element contains 22 protons and 24 neutrons while the other has 22 protons and 25
neutrons.
Isotopes
b. One element has 29 protons and 34 neutrons while the other has 30 protons and 34 neutrons.
Two Different Elements
c. One element has 24 protons and a mass number of 50 while the other element has an atomic
number of 24 and has 28 neutrons.
Isotopes
d. One element is neutral and has 78 electrons and 117 neutrons while the other neutral element
contains 79 electrons and 117 neutrons.
Two Different Elements
8) Complete the following chart:
Isotopic
Isotope Name
Symbol
16
a
O
Oxygen-16
8
8
16
8
8
8
manganese - 56
25
56
25
25
31
Calcium-40
20
40
20
20
20
oxygen - 18
8
18
8
8
10
F
Fluorine- 19
9
19
9
9
10
Rb
rubidium - 87
37
87
37
37
50
Sb
Antimony-123
51
123
51
51
72
N
nitrogen - 15
7
15
7
7
8
Bi
Bismuth-210
83
210
83
83
127
Co
Cobalt-59
27
59
27
27
32
N
Nitrogen-15
15
15
7
7
8
Ge
Germanium-72
32
72
32
32
40
Al
Aluminum-26
13
26
13
13
13
K
Potassium-39
19
39
19
19
20
V
Vandium-51
23
51
23
23
28
b
c
40
Ca
20
d
e
f
g
h
i
j
k
l
m
n
o
19
9
87
37
123
51
15
7
210
83
59
27
15
7
72
32
26
13
39
19
51
23
Atomic
Mass
#
#
#
Number Number protons electrons neutrons
Atomic Mass
9) Determine the average atomic mass of the following mixtures of isotopes.
a) 80.%
127
53 I ,
17%
126
53 I ,
3%
128
53 I
Answer: 126.86amu
b) 50.%
197
79 Au ,
50.%
198
79 Au
Answer: 197.50amu
c) 15%
55
26 Fe ,
85%
56
26 Fe
Answer: 55.85amu
d) 99% 11 H , 0.8% 21 H , 0.2% 31H
Answer: 1.012amu
e) 95%
14
7N,
3%
15
7N,
2%
16
7N
Answer: 14.07amu
f) 98%
12
6C ,
2%
14
6C
Answer: 12.04amu
g) Uranium has 3 isotopes with the following relative abundances: Uranium-234 (0.0058%), U-235
(0.71%), and U-238 (99.23%). Calculate the average atomic mass of uranium:
Answer: 237.849amu
Ions
10) An atom that loses electrons has a net _Positive_ charge and is called a(n) _Cation_______.
11) An atom that gains electrons has a net _Negative_ charge and is called a(n) _Anion______.
12) When a sulfur-32 atom becomes an ion, it typically does so by gaining 2 electrons. What is the isotopic
symbol?
32
-2
______16____________
S
13) How many protons does Na+ have? _11_____ electrons? _10_____
14) How many electrons does P-3 have? _18_____ protons? _15______
15) How many electrons does an ion have with an atomic number of 34 and a charge of -2? _36_____
16) Complete the following chart:
isotopic
symbol
a
b
c
d
e
f
g
63
Cu+
29
15
O-2
8
51
Cr+1
24
25
Mg+2
12
26
Al+3
13
72
Ge+4
32
209
Bi-3
83
atomic
mass
protons electrons neutrons
number number
charge
cation
or
anion?
29
63
29
28
34
+1
Cation
8
15
8
10
7
-2
Anion
24
51
24
23
27
+1
Cation
12
25
12
10
13
+2
Cation
13
26
13
10
13
+3
Cation
32
72
32
28
40
+4
Cation
83
209
83
86
126
-3
Anion