Which of the following compounds are ionic ?
(i)`Li_(3)N`, (ii) `Be_(3)N_(2)` (iii) `Mg_(3)N_(2)` (iv) `Ca_(3)N_(2)`

Options

A. (i),(ii),(iii),(iV)
B. (i),(ii),(iv)
C. (ii),(iii),(iV)
D. (i),(iV)

Answer

1

Explanation

Since it is not easy form energy considerations to gain three electrons to achieve stable noble gas configuration, the formation of the trinegative ion `(E^(3-))` is rare . But nitrogen atoms may gain three electrons and so attain a noble gas configuration forming ionic nitrides containing the `N^(3-)` ion. This is because `N` is the smallest and the most electronegative of all the member of the group.
It takes `2125" kJmol"^(-1)` of energy to form `N^(3-)`. Thus ionic nitrides are formed only by reactive metals which have low ionization enthalpies and can form nitrides with high lattice enthalpies. Thus ,`N` form ionic nitrides such as `Li_(3) N, Be_(3) N_(2), Mg_(3)N_(2)` and`Ca_(3)N_(2)`
As the eletronegativity of the other elements of the group `(P, As, Sb" and "Bi)` is low,most of their analogous compounds are covalent in nature. Thought compunds such as `Na_(3)P` and `Na_(3)Bi` are known, these are not ionic.