# How do atoms become ions?

Calcium atom with electron arrangement K (2),L(8),M(8),N(2) loses two electrons from its outermost shell ( N shell) and forms positive ions called Calcium , $C {a}^{2 +}$ ion.
Oxygen atom with electron arrangement K (2),L(6), gains two electrons from its outermost shell ( L shell) and forms negative ions called oxide , ${O}^{2 -}$ ion.