Chemistry 100
Clark College
Chapter 4 Homework SOLUTION
Follow the homework guidelines given in the syllabus! Show your work, use units and sig figs, where
appropriate.
1. Label the following elements as metals, nonmetals or metalloids.
a) Germanium
Metalloid
b) Manganese
Metal
c) Cesium
Metal
d) Krypton
Nonmetal
2. Give the name and symbol for a unique element (use each only once) that represents:
a) The s-block
Calcium, Ca
b) The d-block
Iron, Fe
c) The actinides
Neptunium, Np
These are all just examples!
d) A halogen
Iodine, I
e) A noble gas
Argon, Ar
f) The p-block
Astatine, At
3. Write the full chemical symbols for carbon-14, cobalt-57, and uranium-238.
carbon-14:
14
6
C
cobalt-57:
57
27
Co uranium-238:
238
92
U
4. Deuterium and tritium are two isotopes of hydrogen, and have one neutron and two neutrons,
respectively. Write the full chemical symbol for deuterium and tritium.
Deuterium: 21H
Tritium: 31H
5. Fill in the missing values in the table below.
Atom
Name
Z
A
Protons
Neutrons
Electrons
Si
Silicon
14
28
14
14
14
Ba
Barium
56
138
56
82
56
Ir
Iridium
77
192
77
115
77
Xe
Xenon
54
131
54
77
54
**I had errors in the silicon and iridium entries! The process remains the same, the result is a very
unstable nucleus.
6. What is the difference between the mass number and the atomic mass given on the Periodic
Table?
The mass number is the sum of the protons and neutrons for a particular isotope of an element. What
we find on the periodic table is the average masses of all isotopes of the element.
Chapter 4 Homework
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Chemistry 100
Clark College
7. Calculate the average molar mass for Chromium, Cr, from the isotopic data given.
Isotope
% Abundance
Atomic Mass
50
Cr
4.345
49.946
52
Cr
51.940
83.789
53
Cr
9.501
52.940
54
Cr
2.365
53.939
Avg. Mass = weighted average of the isotopes
= [0.04345( 49.946 amu)] + [0.83789(51.940 amu)]
+ [0.09501(52.940 amu)] + [0.02365(53.939 amu)] = 51.996 amu
8. Only two isotopes of boron (B) are naturally occurring, their relative abundances are given in the
table below. If the average atomic mass of boron is 10.811, determine the atomic mass of boron11.
Isotope
% Abundance
Atomic Mass
10
19.61
10.013
11
80.39
?
B
B
[
(
)]
[
(
)]
10.811 = 10.013 amu 0.1961 + x amu 0.8039
x = 11.01 amu
9. Predict the charge for ions from the following elements, based on their positions on the periodic
table.
a) S, sulfur.
Group 6 – 8 = -2
b) Br, bromine. Group 7 – 8 = -1
c) Ba, barium. Group 2 = +2
d) Ga, gallium. Group 3 = +3
Chapter 4 Homework
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