Chapter 4, Problem 5A

Interpretation Introduction

Interpretation:

While naming ionic compounds, the relative number of ions is mentioned instead of molecules which is to be explained.

Concept introduction:

Elements are classified as metals and nonmetals on basis of various physical and chemical properties. Some of the physical properties that distinguish metal from nonmetals are malleability, ductility, sonorous sound, brittle or soft nature, melting and boiling temperatures.

Metals can easily release electrons and nonmetals can easily take electrons to attain stability in the configuration.

Answer to Problem 5A

In ${\text{MgCl}}_2$ , ${\text{Mg}}^{2+}$and ${\text{Cl}}^{-}$are present in 1:2 ratio. This is because $\text{Mg}$ exists in +2 state and $\text{Cl}$ in -2 state. So to nullify the +2 charge of $\text{Mg}$ , 2 chlorine atoms are required. Hence the compound is named magnesium dichloride. Therefore it can be said, while naming ionic compounds, the relative number of ions is mentioned instead of molecules.

Explanation of Solution

Metals and nonmetals together form ionic compounds by loss or gain of electrons.

The rules for naming the ionic compounds are as follows:

• On the basis of position in the periodic table, the oxidation state of metal and nonmetal is identified.
• For the name of cation, the metal name is retained as it is and for anion, the root name of the element is suffixed with ‘-ide’.
• Then for the complete name of the ionic compound, cation name and anion names are combined in such a way that cation is placed before the anion name.
• In naming ionic compounds, the relative number of ions is mentioned instead of molecules.

Example: In ${\text{MgCl}}_2$ ,

• $\text{Mg}$ belongs to group 2, so it can release 2 electrons and become ${\text{Mg}}^{2+}$ cation and $\text{Cl}$ belongs to group 17, hence can gain 1 electron and become ${\text{Cl}}^{-}$ anion.
• Now to nullify the +2 charge of $\text{Mg}$ , 2 chlorine atoms are required. Since there are 2 ${\text{Cl}}^{-}$ so ‘di-’ is prefixed before chloride ion.
• So in ${\text{MgCl}}_2$ , ${\text{Mg}}^{2+}$and ${\text{Cl}}^{-}$
• are present in 1:2 ratio. Hence, the compound is named magnesium dichloride.
• Therefore it can be said while naming ionic compounds, the relative number of ions is mentioned instead of molecules.

Conclusion

In ${\text{MgCl}}_2$ , ${\text{Mg}}^{2+}$and ${\text{Cl}}^{-}$are present in 1:2 ratio. This is because $\text{Mg}$ exists in +2 state and $\text{Cl}$ in -2 state. So, to nullify the +2 charge of $\text{Mg}$ , 2 chlorine atoms are required. Hence, the compound is named as magnesium dichloride. Therefore it can be said, while naming ionic compounds, the relative number of ions is mentioned instead of molecules.