# Why do metals lose electrons to form Ions? When does a metal stop losing ions?

It is easy to account for ion formation for the alkali metals. These are supposed to have only the 1 valence electron, which is lost after it oxidizes a non-metal: cf $N a C l , K C l , C s I$ etc. These metals, upon oxidation, have lost all their valence electrons (the which means the outermost electrons). Transition metals have valence electrons amongst the $s$ shell and the $d$ shell. Electrons from the $d$ shell are less penetrating (i.e. and as a consequence less attracted by the nuclear charge), and multiple oxidation states are possible: cf. $F e \left(I\right)$, $F e \left(I I\right)$, $F e \left(I I I\right)$, and even further oxidation states. We remember that oxidation numbers are a formalism, but they are still useful to track metal reactivity.
Most transition metals, $F e$, $C r$, $N i$, for example, have multiple states (including, curiously, negative ones and ones with zero oxidation states). Oxidation states are our attempts to categorize and classify this chemistry.