Chapter U1.21, Problem 5E

Interpretation Introduction

Interpretation:

Examples of three ionic compounds with a metal - to - nonmetal ratio of 2:1 are to be given and total number of valence electrons in each compound has to be specified. Also the compound names have to be given.

Concept introduction:

Ionic compounds are formed between metals and nonmetals. There are about 50 metals and 15 nonmetals which combine in a variety of ways to form large number of ionic compounds. Valence electrons are electrons in the outermost orbit of an atom.

Answer to Problem 5E

The following table shows ionic compounds formed with metals to nonmetals ratio of 2:1.

Metal	Nonmetal	Name of Compound	Number of valence electrons
Na	O	Sodium oxide, Na2O	8
K	O	Potassium oxide, K2O	8
Li	S	Lithium sulfide, Li2S	8

Explanation of Solution

Given information:

Metal to nonmetal ratio in ionic compounds is 2:1.

For a compound to have metal to nonmetal ratio of2:1 the metal must have one valence electron and the nonmetal must have six valence electrons. For every two metal atomsone nonmetal atoms are needed to fulfill noble gas configuration. So the total number of valence electrons in the compound is 8. Hence, the metal must be from group 1A and nonmetal must be from group 6A. Metals of group 1 are lithium, sodium, potassium, rubidium, caesium and francium. Nonmetals of group 6 are oxygen, sulfur, arsenic, antimony, etc. To name the compound, metal name comes first and then nonmetal name changed to “-ide”.

The ionic compounds possible are therefore sodium oxide, potassium oxide, lithium oxide, sodium sulfide, lithium sulfide, etc.

Conclusion

Metals and nonmetals combine in different ratios to form ionic compounds. The total charges on cations and anions must add up to zero. The total number of valence electrons in compounds must be 8 or multiples of 8.