Question

What is the formula for nickel (II) phosphate?

Answer 1

The nomenclature of organic and inorganic chemical compounds is governed by the "international union of pure and applied chemistry". The name of a compound should be systematic and be able to depict and determine the unambiguous formula of a chemical compound.

Complete answer:
Some rules for naming simple inorganic chemical compound are
- The name of the cation or the compound with a positive charge is usually simply the name of the element and followed by the name of the anion.
Hence in nickel (II) phosphate, the cation is nickel (Ni).
- Compounds having more than a single positive charge, or cations are labeled using roman numbers after the name of the cation in brackets.
So, the charge on Ni in nickel (II) phosphate is +2 i.e., $N{{i}^{2+}}$
- Polyatomic anions containing oxygen or oxyanions have suffix -ite for a lesser quantity of oxygen and suffix -ate for the greater quantity of oxygen.
So, phosphate ions have 4 oxygen atoms.
Now, phosphate ions are obtained by removing 3 ${{H}^{+}}$ protons from orthophosphoric acid (${{H}_{3}}P{{O}_{4}}$). So, the charge on phosphate ions is -3.
Hence the anions can be written as $PO_{4}^{3-}$.
Now, the compound nickel (II) phosphate can be written as $N{{I}^{2+}}{{(P{{O}_{4}})}^{3-}}$.
Now, the charge on the compound nickel (II) phosphate can be neutralized if there are 3 atoms of nickel ($N{{i}^{2+}}$) cation and 2 molecules of phosphate ($PO_{4}^{3-}$) anion.
Hence, the formula of nickel (II) phosphate is $N{{i}_{3}}{{(P{{O}_{4}})}_{2}}$.

Note:
It should be noted that ions can be polyatomic. Cations (which are usually metals and positively polyatomic ions) are named before anions (which are usually non-metals and negative polyatomic ions).
Also, some of the prefixes and suffixes indicating oxidation numbers according to the older system are

Oxidation state	Cations and acids	Anions
Lowest	-ous, hypo-	-ite, hypo-
-ous	-ite
-ic	-ate
-ic, per-	-ate, per-
Highest	-ic, hyper-	-ate, hyper-.