Chemistry 103
Homework Problems Answer Key for Chapter 4


1. Give the chemical symbol for each of the following elements.

a. tin
b. lead
c. carbon
d. lithium
e. cobalt
f. copper

The answers are:

a. Sn
b. Pb
c. C
d. Li
e. Co
f. Cu

2. For each of the following chemical symbols, give the name of the corresponding element.

a. U
b. Fe
c. Au
d. Sn
e. Sb
f. Si
g. Sr
h. S

The answers are:

a. uranium
b. iron
c. gold
d. tin
e. antimony
f. silicon
g. strontium
h. sulfur

3. Write the formula for each of the following substances, listing the elements in the given order.

a. a molecule containing one phosphorous atom and three chlorine atoms
b. a molecule containing two boron atoms and six hydrogen atoms
c. a compound containing one calcium atoms for every two chlorine atoms
d. a molecule containing one carbon atom and four bromine atoms
e. a compound containing two iron atoms for every three oxygen atoms
f. a molecule containing three hydrogen atoms, one phosphorous atom and four oxygen atoms.

a. PCl3
b. B2H6
c. CaCl2
d. CBr4
e. Fe2O3
f. H3PO4

4. Write the Atomic Symbol (AZX) for each of the isotopes described below.

a. Z = 8, number of neutrons = 9

First, go to the periodic table and find which element is number 8. You will find that this is oxygen. Next, determine A by adding 8 and 9. Thus the representation is: 178O

b. the isotope of chlorine for which A = 37

First, go to the periodic table and find what number element chlorine is. You will find that it is element 17. Thus, the representation is: 3717Cl

c. Z = 27, A = 60

First, go to the periodic table and find which element is number 27. You will find that this is cobalt. Thus the representation is: 6027Co

d. number of protons = 26, number of neutrons = 31

First, go to the periodic table and find which element is number 26. You will find that this is iron. Thus the representation is: 5726Fe

e. the isotope of I with a mass number of 131

First, go to the periodic table and find what number element iodine is. You will find that it is element 53. Thus, the representation is: 13153I

f. Z = 3, number of neutrons = 4

First, go to the periodic table and find which element is number 3. You will find that this is lithium. Next, determine A by adding 3 and 4. Thus the representation is: 73Li

5. How many protons and neurons are contained in the nucleus of each of the following atoms. Assuming each atom is unchanged, how many electrons are present?

a. 24494Pu
b. 24195Am
c. 22789Ac

Remember that the number of protons and neutrons are the same. The number of protons or electrons are determined by the mass number, A in the general form: AZX. And the number of neutrons are determined by the difference of the mass number and the atomic number, A - Z in the general form. With this information, you should be able to make up the following table:

Atom p+ n e-
a. 24494Pu 94 150 94
b. 24195Am 95 146 95
c. 22789Ac 89 138 89


6. Complete the following table.

Use the same relationships that were used in the previous table to generate the missing information and complete the following table:

Name Symbol Atomic Number Mass Number Neutrons
sodium ? = 2311Na 11 23 ? = 12
nitrogen 157N ? = 7 ? = 15 ? = 8
? = barium 13656Ba ? = 56 ? = 136 ? = 80
lithium ? = 93Li ? = 3 ? = 9 6
boron ? = 115B 5 11 ? = 6


7. How are the elements ordered in the periodic table?

In order of increasing atomic number (or increasing number of e- and p+).

8. Write the number and name (if any) of the group (family) to which each of the following elements belongs.

a. cesium
b. Ra
c. Rn
d. chlorine
e. strontium
f. Xe
g. Rb

Chemical Name Family Name Group Number
a. Cs, Cesium Alkali 1A
b. Ra, Radium Alkaline 2A
c. Rn, Radon Noble Gas 8A
d. Cl, Chlorine Halogen 7A
e. Sr, Strontium Alkaline 2A
f. Xe, Xenon Noble Gas 8A
g. Rb, Rubidium Alkali 1A


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