Name: _______________________________________________ Date: ______________________________ Period: _________
Unit 4 Test Study Guide
Part 1: History of the Atom
Sketch the atom models for the following scientists and summarize their experiments that led to their models.
Democritus
Greek who believed in atomos (matter made up of indivisible atoms)
John Dalton
British chemist who developed five postulates of atomic theory, thought they were indivisible
spheres like Democritus
J. J. Thomson
Discovered negatively charged electron through cathode ray tube experiment
Ernest Rutherford
Niels Bohr
Discovered nucleus, and most of atom was empty space
Electrons traveled on circular, quantized orbits around nucleus
Atomic Model Comparison
Sketch each scientist’s model of the atom in the boxes given.
Thomson
Bohr
Rutherford
Democritus/Dalton
Part 2: The Atom
Complete the following table.
Element
Symbol
Atomic
#
Atomic
Mass
# protons
#
neutrons
#
electrons
Argon
Ar
18
40
18
22
18
Cadmium
Cd
48
112
48
64
48
Praseodymium Pr
59
140
59
81
59
Lead
Pb
82
207
82
125
82
Tungsten
W
74
184
74
110
74
Nuclear
Symbol
40
Ar
18
112
Cd
48
140
Pr
59
207
Pb
82
184
W
74
Part 3: The Ion
Complete the following table.
Element
Ion
Symbol
Atomic #
Atomic
Mass
# protons
# neutrons
# electrons
Cobalt
Co2+
27
59
27
32
25
Nuclear Symbol
(include charge)
59
Co2+
27
27 3+
Al
13
106
Pb2+
46
133 2+
Cs
55
127 I
53
Aluminum
Al3+
13
27
13
14
10
Palladium
Pb2+
46
106
46
60
44
Cesium
Cs2+
55
133
55
78
53
Iodine (-1)
I-
53
127
53
74
54
Atomic Mass
# protons
# neutrons
# electrons
Part 4: The Isotope
Complete the following table.
Element
Hyphen Notation
Atomic #
Vanadium
Vanadium-51 23
51
23
28
23
Vanadium
Vanadium-52 23
52
23
29
23
Barium
Barium-139
56
139
56
83
56
Lead
Lead-209
82
209
82
127
82
Silver
Silver-109
47
109
47
62
47
Nuclear
Symbol
51
V
23
52
V
23
139
Ba
56
209
Pb
82
109
Ag
47
Part 5: Weighted Average Atomic Mass
Solve the following problems + round your answer to the correct number of significant figures.
1. What is the average atomic mass of silicon given the following abundance information on the isotopes of
silicon?
Mass number
Abundance
Si-28
92.21 %
Si-29
4.70 %
Si-30
3.09 %
92.21 = 0.9221
100
0.9221(28) = 25.8188
4.70 = 0.0471
100
0.0471(29) = 1.3659
3.09 = 0.0309
100
0.0309(30) = 0.927
28.1117  28.1 amu
2. Calculate the atomic mass of potassium if the abundance atomic masses of the isotopes making up its naturally
occurring samples are as given below.
93.12 = 0.9312 (38.964) = 36.283276
Isotope
Relative abundance Atomic Mass
100
potassium-39 93.12 %
38.964 amu
potassium-41
6.88
40.962 amu
6.88 = 0.0688 (40.962) = 2.8181856
100
39.101461  39.101 amu
3. What is the average atomic mass of hafnium given the following abundance information on its isotopes?
Mass number
Abundance
Hf-176
5%
Hf-177
19 %
Hf-178
27 %
Hf-179
14%
Hf-180
35%
5/100 = 0.05(176) =
19/100 = 0.19(177) =
27/100 = 0.27(178) =
14/100 = 0.14(179) =
35/100 = 0.35(180) =
8.8
33.63
48.06
25.06
63
178.55 amu  180 amu
4. Neon has two isotopes. There are 800 atoms of Neon (with an average atomic mass of 20.3405 amu). 70% of
the atoms are Neon-20 (19.8865 amu). What is the mass of the other Neon isotope? (Write it in hyphen
notation and nuclear).
70% - 19.8865
___% - ?
Average atomic mass = 20.3405 amu
100% - 70% = 30%
70% - 19.8865  0.70 – 19.8865
30% - ?
 0.30 - ?
0.70(19.8865) + 0.30(?) = 20.3405
13.92055 + 0.30(?) = 20.3405
-13.92055
-13.92055
0.30(?) = 6.41995
0.30
0.30
? = 21.399833  The atomic mass of the 2nd isotope is 21.3998 amu.