Answer: Its bonds are formed by large differences in electronegativity.
Explanation:
An ionic bond is formed when an element completely transfers its valence electron to another element. The element which donates the electron is known as electropositive element and the element which accepts the electrons is known as electronegative element. This bond is formed between a metal and an non-metal.
Covalent bond is formed by sharing of electrons between non metals.
As electronegativity of calcium is 1 and that of chlorine is 3.16, there is a difference of (3.16-1) =2.16, which is large and thus form ionic bond.
