If carbon atom is tetravalent while oxygen atom is divalent so when they combine together the result should be $\ce{C2O4}$ then how are there compounds of formulas with $\ce{CO2}$, $\ce{CO3}$ and others? How do they bond?

• $\ce{CO2}$ is not a radical. – bon Feb 26 '16 at 10:14
• Yes sorry i got confused .. but i want to ask about their formation regarding valencies – user27247 Feb 26 '16 at 10:18
• Could you please tell me first what you would consider the definition of a radical? – M.A.R. Feb 26 '16 at 10:19
• Group of atoms that act like one atom during the chemical reaction .. ? I don't know much, i am asking so may someone correct my information about radicals – user27247 Feb 26 '16 at 10:29

This is the lewis structure of $\ce{CO_2}$.Each bond symbolises of sharing of two electrons.One from oxygen and other from carbon.

You can imagine $\ce{CO_2}$ as such.

Formation of $\ce{CO_2}$ can be calculted by transfer of valencies but cannot be explained. And there are other compounds which cannot be calculated by valency transfer but can be explained by Kossell-Lewis approach.
$\ce{CO_2}$ is not a radical