I like to write and name chemical formulas, but some formulas just confused me really bad, so I would like help getting back on track.

Question

I don't understand this.

NiPO4: I know that Ni = Nickel, and PO4 = Phosphate, but how come there isn't the -3 charge on it?

This is what I had done:

NiPO4 = Nickel(I) Phosphate.

my friend got something else, she got:

Nickel(III) Phosphate. Where did she get the three from?

Answer 1

If the formula is NiPO4, then since PO4 ion has a -3 charge, the Ni must have +3 charge (since all compounds are zero charged). So we write Ni(III) phosphate.