Chapter U1.21, Problem 8E

Interpretation Introduction

Interpretation:

Cations and anions with appropriate charges for given ionic compounds are to be given. The chemical formula for each compound needs to be determined.

Concept introduction:

Ionic compounds are formed between metals and nonmetals. Metal ions with positive charges are called cations and nonmetal ions with negative charges are called anions.

Answer to Problem 8E

The following table shows cations, anions and formula of compounds.

S. no	Name of compound	Cation	Anion	Formula of compound
a.	Magnesium oxide	Mg2 +	O2-	MgO
b.	Rubidium bromide	Rb +	Br-	RbBr
c.	Strontium iodide	Sr2 +	I-	SrI2
d.	Beryllium fluoride	Be2 +	F-	BeF2
e.	Aluminium chloride	Al3 +	Cl-	AlCl3
f.	Lead sulfide	Pb2 + , Pb4 +	S2-	PbS, PbS2

Explanation of Solution

Given information:

Following compounds are given.

a.	Magnesium oxide
b.	Rubidium bromide
c.	Strontium iodide
d.	Beryllium fluoride
e.	Aluminium chloride
f.	Lead sulfide

1. Magnesium oxide: magnesium belongs to group 2 of the periodic table. It can lose 2 electrons and form cation with 2 positive charges. Oxygen belongs to group 6 and can gain 2 electrons to form anion with 2 negative charges. So one magnesium atom can combine with 1 oxygen atom to form MgO. Total valence electrons are 8. To name the compound, the metal name comes first and then the nonmetal name is changed to “-ide”. So, the name of the compound formed is magnesium oxide .
2. Rubidium bromide: Rubidium belongs to group 1 of the periodic table. It can lose 1 electron and form cation with 1 positive charge. Bromine belongs to group 7 and can gain 1 electron to form anion with 1 negative charge. Rubidium has 1 valence electrons and bromine has 7 valence electrons. So 1 rubidium atom can combine with 1 bromine atoms to form RbBr. Total valence electrons are 8. To name the compound, the metal name comes first and then the nonmetal name is changed to “-ide”. So, the name of the compound formed is rubidium bromide .
3. Strontium iodide: Strontium belongs to group 2 of the periodic table. It can lose 2 electrons and form 2 positive charges. Iodine belongs to group 7 and can gain 1 electron to form 1 negative charge. Strontium has 2 valence electrons and iodine has 7 valence electrons. So one strontium atom can combine with 2 iodine atoms to form SrI₂. Total valence electrons are 16. To name the compound, the metal name comes first and then the nonmetal name is changed to “-ide”. So the name of the compound formed is strontium iodide .
4. Beryllium fluoride: Beryllium belongs to group 2 of the periodic table. It can lose 2 electrons and form 2 positive charges. Fluorine belongs to group 7 and can gain 1electron to form 1 negative charge. Beryllium has 2 valence electrons and fluorine has 7 valence electrons. So 1beryllium atom can combine with 2 fluorine atoms to form BeF₂. Total valence electrons are 16. To name the compound, the metal name comes first and then the nonmetal name is changed to “-ide”. So the name of the compound formed is beryllium fluoride .
5. Aluminum chloride: Aluminium belong to group 3 of the periodic table. It can lose 3 electrons and form cation with three positive charges. Chlorine belongs to group 7 and can gain 1 electron to form anion with one negative charge. So one aluminum atom can combine with 3 chlorine atoms to form AlCl₃. Total valence electrons are 24. To name the compound, the metal name comes first and then the nonmetal name is changed to “-ide”. So the name of the compound formed is aluminum chloride .
6. Lead sulfide: lead belongs to group 4 of the periodic table. It can lose 4 electrons and form 4 positive charges. Sulfur belongs to group 6 and can gain 2 electrons to form two negative charges. Lead has 4 valence electrons and sulfur has 6 valence electrons. So 1 lead atom can combine with 2 sulfur atoms to form PbS₂. Total valence electrons are 16. To name the compound, the metal name comes first and then the nonmetal name s changed to “-ide”. So the name of the compound formed is lead sulfide. Lead also has a valency of 2. So, it can form another compound with sulfur where one atom of lead combines with 1 atom of sulfur forming PbS.

Conclusion

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