Question

Write down the chemical formula for:
a. Magnesium nitride
b. Calcium nitrate
c. Sodium nitrite

Answer 1

Hint: To write the chemical formula of a compound we first need to write the number of valence electrons, exchange it with corresponding compound and then write it as the subscript.

Complete answer:
To write the chemical formula of a compound we need to follow some steps that will make our task simpler. The steps are as given below.
1. First, write down the symbol of every element or ion which combine to form a molecule of the compound side by side. While writing the formula of a compound containing a metal and a non-metal, the symbol of the metal is written first followed by that of the non-metal. We need to note here that two metals do not join up to form compounds.
2. Then write the number of valence electrons of each element/ion.
3. Interchange the valencies of the elements and write as the subscript. Write them close together and ignore ‘1’ to obtain the formula.
4. The radical polyatomic ions must be written in brackets before the subscript is written. In case the number of polyatomic ions is one, the bracket is not required. For example NaOH.
5. Whenever applicable write simple ratios of the valencies.
6. In the end, the final formula must be written without any sign of charge.
Now, moving to the compounds given in the question, the first is magnesium nitrate. We know that $Mg$ is the symbol of magnesium and$N^{3-}$ is formula for nitride. Combining the two we get the formula of Magnesium nitride as $M{g_3}{N_2}$ .
Second compound is Calcium nitrate. We know that $Ca$ is the symbol of calcium and $N{O_3}^ - $ is formula for nitrate. Combining the two we get the formula of Calcium nitrate as $Ca{(N{O_3})_2}$ .
Third compound is Sodium nitrite. We know that $Na$ is the symbol of sodium and $N{O_2}^ - $ is formula for nitrite. Combining the two we get the formula of Sodium nitrite as $NaN{O_2}$ .

The chemical formula of Magnesium nitride is $M{g_3}{N_2}$ , chemical formula of calcium nitrate is $Ca{(N{O_3})_2}$ and of sodium nitrite is $NaN{O_2}$ .

Note:
We should not get confused in naming these three salts as we know nitride is used for $N^{3-}$, nitrite for ${NO_2}^-$ and nitrate for ${NO_3}^-$.