Question

What is the formula formed by a copper (II) cation and nitride anion?

Answer 1

Hint: To form an ionic compound there needs a bond formation between a cation and anion. We have given a cation and an anion; these two opposite ions form a bond between them satisfying the respective oxidation states.

Complete answer:
Let us formulate the given condition;
Formation of an ionic compound can also be defined as the synthesis reaction of the same from opposite types of ions i.e. cation and anion. The general reaction is given as;
\[X+Y\to XY\]
where, either of the ions i.e. X or Y can be cation or anion.
Now, concentrating on given condition;
Copper is given as a cation with oxidation state of +2 whereas nitride is given as anion; which has a charge of -3. We need to use a criss-cross method to satisfy the valances and form the product.
Copper has a charge of +2 thus, will require two nitrogen atoms to satisfy the charge.
Nitride has a charge of -3 thus, will require three copper atoms to satisfy the charge.
Hence, the reaction will take place as such; $3C{{u}^{2+}}+2{{N}^{3-}}\to C{{u}_{3}}{{N}_{2}}$ forming a product as $C{{u}_{3}}{{N}_{2}}$ i.e. copper nitride.

Note:
Do note that the criss-cross method is important when we talk about formation of an
ionic compound. The valency (oxidation state atom carries) is the most viable aspect to use this phenomenon to take place.