Here's why:

* Metallic bonding: Metals are held together by a "sea" of delocalized electrons. These electrons are not tightly bound to any specific atom and can move freely throughout the metal.

* Electropositivity: Metals have a tendency to lose electrons due to their relatively low electronegativity. This means they are more likely to give away electrons than to gain them.

* Formation of cations: When a metal atom loses one or more electrons, it becomes a positively charged ion (cation). This is because it now has more protons (positive charge) than electrons (negative charge).

Example:

Sodium (Na) is a metal. It has one valence electron (electron in its outermost shell). When sodium reacts, it loses this electron to form a sodium ion (Na+), which has a +1 charge.

Key point: Metals donate electrons to form positive ions, which is a fundamental characteristic of their chemical behavior.