Here's why:

* Electrons are negatively charged: Metals have a tendency to lose electrons, which are negatively charged particles.

* Cations are positively charged: When a metal atom loses electrons, it becomes positively charged because it now has more protons (positive) than electrons (negative).

* Example: Sodium (Na) has one electron in its outermost shell. When it loses that electron, it becomes a sodium cation (Na+), which has a +1 charge.

Let me know if you have any other questions!