What is the difference between a single-valent ionic compound and a multi-valent ionic compound?

Question

Also, is a covalent compound only between two non-metals? Thanks!

Answer 1

Single Valent Ionic Compound is Sodium Chloride.
Sodium can only form a one-bond ionic compound. It loses only one electron when formimg its ion. Similarly Chlorine can only form a one-bond ionic compound. It gains only one election when forming its ion.

Bivalent Ionic Compound is Magnesium Chloride.
Magnesium can only form a two-valent ionic compound. It loses two electrons when forming its ion. Since from above Chlorine can only form a one-bond ionic compound, because it gains only one electron, two chlorine atoms are needed in order to ionically combine with magnesium. Hence magnesium is described as a bi-Valent compound.
Valency is an atoms ability to form a given number of bonds.
The group 1 metals are mono valent, they can only form 1 bond.
Group 2 metals are bi-valent they can form 2 bonds, &c.

Answer 2

To answer the second part ofthe question (the 1st part has already been answered). No, metals can be involved in covalent bonding. In reality no bond is entirely ionic or covalent but most are more of one than the other.
A predominantly covalent compound involving a metal would be aluminium chloride (AlCl3). Another would be lithium fluoride (LiF). The reasons for this are too long to include here.