Question

objective: students will understand the concept of covalent bonding (the sharing of electrons).
a molecule of carbon dioxide (co₂) contains one carbon atom and two oxygen atoms.
carbon has 4 valence electrons, and oxygen has 6 valence electrons.
part a:
explain why carbon forms two double covalent bonds in a co₂ molecule instead of single bonds.

Explanation:

In a \(CO_2\) molecule, carbon has 4 valence electrons and needs 4 more to complete its octet (achieve a stable electron configuration like noble gases). Each oxygen atom has 6 valence electrons and needs 2 more. If carbon formed single bonds (\(C - O\)), each single bond shares 2 electrons. With two oxygen atoms, carbon would only gain 2 electrons from each single bond (\(2\times1 = 2\) additional electrons per \(O\) atom, total \(4\) from two \(O\) atoms). But in double bonds (\(C = O\)), each double bond shares 4 electrons. Two double bonds (\(2\times2= 4\) additional electrons from each \(O\) atom, total \(8\) for carbon's octet). Also, oxygen can achieve its octet (6 + 2 from double bond = 8) through double - bonding.

Answer:

Carbon forms two double covalent bonds in \(CO_2\) to achieve a stable octet (8 valence electrons). Carbon has 4 valence electrons. Each double bond (\(C = O\)) shares 4 electrons (2 from carbon and 2 from oxygen). With two double bonds, carbon gets \(4 + 4=8\) electrons. Oxygen (6 valence electrons) also gets \(6 + 2 = 8\) electrons per \(O\) atom (from double bond) to complete its octet. If there were single bonds (\(C - O\)), carbon would not reach an octet (e.g., \(4+2 = 6\) with one \(O\) single - bond, and even with two \(O\) single - bonds \(4+(2\times1)=6\) which is less than 8).