How can one determine if a bond between two atoms is ionic covalent or metallic?

By the Pauling rule, of EN

Explanation:

EN means electronegativity, the ability of atoms to attract electrons.

In the periodic table each atom, has a value of EN.

When there are two atoms bonded, you must substract the EN (the high - the low) → ΔEN

It depends on the ΔEN, that you can define a bond as ionic, covalent or metallic.

Ionic ΔEN → > 1.7

Covalent polar 0.4 1.7

Covalent non polar 0.4 < ΔEN

Two metals have always a metallic bond