Atomic numbers of Calcium $\left(Ca\right)=20$ and chlorine$\left(Cl\right)=17$. Explain the formation of calcium chloride with the help of an electron dot diagram.

$Ca(Z=20);$Electronic configuration : 2, 8, 8, 1

$Cl(Z=17);$Electronic configuration : 2,8,7
The chlorine atom's electronic configuration makes it evident that it possesses seven electrons in its outermost shell. Therefore, for a chlorine atom to be in a noble gas configuration, it needs one more electron.
When a calcium atom interacts with two other chlorine atoms to form an ionic compound, each chlorine atom gains an electron from the calcium atom.
As a result, calcium becomes positive in nature because it donates electrons to the chlorine atom, and the chlorine atom becomes negative in nature.

The electron dot structure of the formation of calcium chloride is as follows:

Hence, the formula of calcium chloride is $CaC{l}_2$ .