Chem 121: Homework 3
Due at the beginning of class on Tuesday, Apr. 26th or Wednesday, Apr. 27th (date depends on your section.)
Do the problems from chapters 4 and 9, in bold below, and problems A through E.
Chap 4: 24, 26, 36, 38, 44, 46, 50, 88, 90, 92, 94, 96, 98, 108.
Chap 9: 52, 56, 58, 60, 64, 72, 76abc, 78, 92, 100.
A. Complete entries 1-7 of the following table:
isotope
symbol
1.
number of
protons
number of
neutrons
number of
electrons
30
32
30
18
8O
2.
3.
4.
68
33 As
5.
6.
7.
B. According to the Periodic Table, the atomic mass of chlorine is 35.45 amu. However, there does not exist a single Cl atom in the
universe that has this mass. Explain why this is true.
C. Calculate the number of helium atoms in a birthday balloon containing 2.3 grams of helium gas, using the average mass of one
atom of helium (from the periodic table) and the conversion factor between g and amu. Write your answer both in scientific and
standard (regular) notation. Compare your answer to the picture on the bottom of page 56 of your textbook: What can you critique
about this picture?
D. Use a method similar to that in problem C (that is, by using atomic mass and the relationship between grams and amu as
conversion factors) to calculate the mass, in grams, of a silver ring that is 100% Ag and is composed of 1.3x1026 atoms of silver.
E. For each of these elements: S, P, Sr, Li, F, Pd, Te
1. write the full electron configuration
2. circle the valence electrons in the full configuration
3. write the configuration a second time, using a noble gas core
Suggested for extra practice (do not turn in):
Chap 4: 35, 37, 43, 45, 47, 49, 87, 89, 91, 93.
Chap 9: 51, 53, 55, 57, 59, 75, 77.