Answer:
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 < ΔEN > 1.7
Covalent non polar 0.4 < ΔEN
Two metals have always a metallic bond
