Question

why metals have the tendency to form cations?

Answer 1

Every element has a tendency to become stable by attaining the octet configuration. Most metal have less than 4 electrons in their valence shell. They can attain the octet configuration either by losing less than 4 electron(1, 2 or 3 electron) or by accepting more than 4 electrons(5, 6 or 7 electrons). But accepting so many electron and accommodating them in the valence shell is impossible. That's why it is easy to lose less than 4 electrons than to gain more than 5 electrons. This is the reason why they have a tendency to form cations by losing electrons.

Answer 2

Metals lose electron as they are electropositive in nature.
They lose electron to attain octet configuration.(8 electrons in outermost shell)