What does multivalent ion mean?

Answer 1

Multivalent ions are just a few ions (like Fe) that have more than one valence. We have no way of telling which one it is when we write the words so we use roman numerals like I and II .

When they are in a formula we can tell which one it is by working backwards and using some deductive reasoning.

So, lets say you have FeCl2

We know that Cl is always -1 so if we have to have 2 chlorines to balance the charge of one Fe then the Fe must be charged +2

That Fe is Iron II

This compound would be written as Iron II chloride.

There are only a few multivalenet ions you will deal with regularly

They are Iron (Fe), Tin (Sn), Mercury (Hg), Copper (Cu), Gold (Au), Manganese (Mn), Lead (Pb), Cobalt (Co), and Chromium (Cr). There is an older way of naming these without the Roman Numerals. Iron II is also called Ferrous and Iron III is ferric. The "ous" and the "ic"suffix tell you the charge. The "ous" ending is always a lower oxidation number than "ic".