Question

draw the electron dot structure for cao

Answer 1

Hope it helps  The valency of Ca is 2 and valency of O is 6 so Ca loses the 2 electrons and O gains it to become stable

Answer 2

Answer:

For formation of a neutral ionic compound, the charges on cation and anion must be balanced. The cation is formed by loss of electrons by metals and anions are formed by gain of electrons by non metals.  

Here calcium is having an oxidation state of +2 called as $Ca^{2+}$ cation and oxide $O^{2-}$ is an anion with oxidation state of -2. Thus they combine and their oxidation states are exchanged and written in simplest whole number ratios to give neutral $CaO$.

Electronic configuration of calcium

$[Ca]:20:1s^22s^22p^63s^23p^64s^2$

Calcium atom will lose electron to gain noble gas configuration and form calcium cation with +2 charge.

$[Ca^{2+}]:18:1s^22s^22p^63s^23p^6$

Electronic configuration of oxygen:

$[O]:8:1s^22s^22p^4$

Oxygen atom will gain two electrons to gain noble gas configuration and form oxide ion with -2 charge.

$[O^{2-}]:10:1s^22s^22p^6$