How do you determine if a compound is ionic?
If it is a binary salt,
Does the metal come from the far left of the Periodic Table (as we face it)? Does the non-metal come from the right of the Periodic Table. If so, the compound is likely ionic.
Alkali metals and alkaline earth metals comprise Group I and Group II on the Periodic Table. These are likely to form ionic salts with the common non-metals: the halogens and the chalcogens, as these are very likely to form
Are the metals and non-metals closer together on the Periodic Table? Their compounds might have some measure of covalency.