Chapter U1.21, Problem 7E

Interpretation Introduction

Interpretation:

Formulas and compound names of ionic compounds with given metals and nonmetals are 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 7E

The following table shows ionic compounds formed with given metals to nonmetals.

S. no	Metal	Nonmetal	Formula	Name of compound
a.	Al	Br	AlBr3	Aluminium bromide
b.	Al	S	Al2S3	Aluminium sulfide
c.	Al	As	AlAs	Aluminium arsenide
d.	Na	S	Na2S	Sodium sulfide
e.	Ca	S	CaS	Calcium sulfide
f.	Ga	S	Ga2S3	Gallium sulfide

Explanation of Solution

Given information: Following metals and nonmetals are given.

a.	Al	Br
b.	Al	S
c.	Al	As
d.	Na	S
e.	Ca	S
f.	Ga	S

1. Al and Br - Aluminium belong to group 3 of the periodic table. It can lose 3 electrons and form three positive charges. Bromine belongs to group 7 and can gain 1 electron to form one negative charge. So one aluminium atom can combine with 3 bromine atoms to form AlBr₃. To name the compound, metal name comes first and then nonmetal name changed to “-ide”. So the name of compound formed is aluminium bromide .
2. Al and S - Aluminium belong to group 3 of the periodic table. It can lose 3 electrons and form three positive charges. Sulfur belongs to group 6 and can gain 2 electrons to form two negative charges. Aluminium has 3 valence electrons and sulfur has 6 valence electrons. So two aluminium atoms can combine with 3 sulfur atoms to form Al₂S₃. Total valence electrons are $24\left(2\times 3\right)+\left(3\times 6\right)$. To name the compound, metal name comes first and then nonmetal name changed to “-ide”. So the name of compound formed is aluminium sulfide .
3. Al and As - Aluminium belong to group 3 of the periodic table. It can lose 3 electrons and form three positive charges. Arsenic belongs to group 5 and can gain 3 electrons to form three negative charges. Aluminium has 3 valence electrons and arsenic has 5 valence electrons. So one aluminium atom can combine with 1 arsenic atom to form AlAs. Total valence electrons are 8. To name the compound, metal name comes first and then nonmetal name changed to “-ide”. So the name of compound formed is aluminium arsenide .
4. Na and S - Sodium belong to group 1 of the periodic table. It can lose 1 electron and form one positive charge. Sulfur belongs to group 6 and can gain 2 electrons to form two negative charges. Sodium has 1 valence electron and sulfur has 6 valence electrons. So two sodium atoms can combine with 1sulfur atom to form Na₂S. Total valence electrons are 8. To name the compound, metal name comes first and then nonmetal name changed to “-ide”. So the name of compound formed is sodium sulfide .
5. Ca and S - Calcium belong to group 2 of the periodic table. It can lose 2 electrons and form two positive charges. Sulfur belongs to group 6 and can gain 2 electrons to form two negative charges. Calcium has 2 valence electrons and sulfur has 6 valence electrons. So one calcium atom can combine with 1 sulfur atom to form CaS. Total valence electrons are 8. To name the compound, metal name comes first and then nonmetal name changed to “-ide”. So the name of compound formed is calcium sulfide .
6. Ga and S - Gallium belong to group 3 of the periodic table. It can lose 3 electrons and form 3 positive charges. Sulfur belongs to group 6 and can gain 2 electrons to form two negative charges. Gallium has 3 valence electrons and sulfur has 6 valence electrons. So 2 gallium atoms can combine with 3 sulfur atoms to form Ga₂S₃. Total valence electrons are $24\left(2\times 3+3\times 6\right)$. To name the compound, metal name comes first and then nonmetal name changed to “-ide”. So, the name of compound formed is gallium sulfide .

Conclusion

Metals and nonmetals combine to form ionic compounds. The charges on metal cations and nonmetal anions in ionic compounds add up to zero.