Chapter 7, Problem 67A

Interpretation Introduction

Interpretation: The compounds which are not ionic need to be identified.

Concept Introduction: Ionic compounds are formed by the chemical combination of a metal and a non-metal. Here, metals tend to be electron-rich; thus, they lose electron/s to form a cation. Similarly, non-metals tend to be electron deficient, thus, they gain electron/s to form an anion. These cations and anions can combine in a fixed ratio to form ionic compounds.

Answer to Problem 67A

The compounds which are most likely not ionic are ${\text{H}}_{\text{2}}\text{O}$ , ${\text{CO}}_{\text{2}}$ , ${\mathrm{SO}}_2$ , and ${\text{NH}}_{\text{3}}$ .

Explanation of Solution

Reason for correct option/s:

Considering option (a), ${\text{H}}_{\text{2}}\text{O}$ is a covalent compound because the bond between H and O is covalent in nature. Thus, it is not an ionic compound.

Considering option (c), ${\text{CO}}_{\text{2}}$ is also a covalent compound. Here, the bond between C and O is formed by sharing of electrons. Also, both C and O are non-metals; thus, they cannot form an ionic compound.

Considering option (e) ${\mathrm{SO}}_2$ is also a covalent compound. The bond is formed by sharing of electrons. Also, both S and O are non-metals thus, the bond cannot be ionic.

Considering option (f), ${\text{NH}}_{\text{3}}$ is also not ionic but covalent. The bond between N and H is formed by sharing of electrons hence it is a covalent bond.

Therefore, compounds given in option (a), (c), (e), and (f) are not ionic compounds.

Conclusion

Reason for incorrect option/s:

Considering ${\text{Na}}_{\text{2}}\text{O}$ , the bond between Na and O is formed by the transfer of electrons from two Na atoms to an O atom. Here, Na is a metal with 1 valence electron which can be easily lost to form ${\text{Na}}^{+}$ ion.

Similarly, O is a non-metal with 6 valence electrons. It can gain two electrons to form ${\text{O}}^{2-}$ ion. To form an ionic compound, Na and O must combine in a 2:1 ratio as 2 Na atoms are required for one oxygen atom to complete its octet.

Therefore, ${\text{Na}}_{\text{2}}\text{O}$ is an ionic compound and option (b) is incorrect.

Considering CaS, Calcium is a metal and sulphur is a non-metal. Ca can lose two electrons to form ${\text{Ca}}^{2+}$ ion and S can gain two electrons to form ${\text{S}}^{2-}$

ion. Since both Ca and S have equal charges, they can combine in 1:1 ratio to form an ionic compound.

Therefore, CaS is an ionic compound and option (d) is incorrect.