Which elements usually lose their valence electrons when they bond

Metals, for example Cesium and Francium

Ionic bonding is when the valence electron is stripped from the molecule when bonding to equilibrate charge energy. The opposite is covalent bonding, where electrons are not lost but shared.

Ionic bonding is seen when metals interact with non metals and other metals

the element that loses the valence electron is the one that is more positively charged. The element that gains the electron was more negatively charged.