Question

Valency of O2is -2 and valency of C is +4, then how CO3 is formed?

Answer 1

Basically, CO3 exists as an anion with -2 negative charge ( thus forming Na2CO3 and such). CO3 is formed due to covalent bonding between three oxygen and one carbon. Covalent bonding means sharing of electrons between two atoms. This structure is formed like this : one atom of oxygen shares two of its electrons with the carbon atom and takes(shares) two electrons from carbon to attain an octet. The carbon atom now has 6 electrons in outermost shell. Two other oxygen atoms share one of their electrons with carbon which gives octet config to carbon but each of those oxygen atoms have only seven electrons, so to get stable it needs to give out one electron each, I.e., it has one electron extra. Thus, it has a negative charge of 2. It might be difficult to understand right now but don't worry, you'll be taught in detail in 10th-11th grade.