Question

Covalency of carbon in the $\text{CO}$ molecule is three because:
A. An unexcited carbon atom has two unpaired electrons.
B. the carbon atom can be an acceptor of an electron pair.
C. The carbon atom has four valence electrons.
D. maximum covalency of carbon is three.

Answer 1

Hint: Covalent is the number of bonds an element forms with other elements in a molecule. Valency and covalency are different. Valency is the number of electrons lost or gained to achieve stable electronic configuration. Covalency depends upon the valency.

Complete step by step answer:
We have to know the number of bonds carbon forms with oxygen which is termed as covalency. For that, we have to draw the Lewis structure.
The steps to draw the Lewis structure are:
-Find the number of valence electrons for each of the atoms in the molecule.
-The number of valence electrons is usually the same as the group number where the element is located.
-The number of valence electrons of carbon is $4$ and the number of valence electrons of oxygen is $6$.
-Count the total number of valence electrons in the molecule.
-Total valence electrons$=$ valence electrons of carbon $+$ valence electrons of oxygen$=4+6=10{\text{e}}^{-}$
-Use octet rule to find the number of octet electrons atoms should have.
-Carbon and oxygen should have eight electrons.
-Place the valence electrons around each atom and draw the bonds for each pair of electrons.
Thus carbon-oxygen bonds can be represented as .
-Therefore carbon forms three covalent bonds with oxygen by triple bond because carbon can be an acceptor of electron pairs. Here two bonds are covalent and one is coordinate covalent bond. Coordinate covalent bond is formed by donating the lone pair of electrons from oxygen to carbon since the carbon has the ability to accept electrons.
Therefore, the option B is correct.

Note: Carbon is an element having four valence electrons. So to form a stable configuration, it must either lose or gain electrons. It has the ability to both gain and lose electrons. This is the reason for forming a coordinate covalent bond between carbon and oxygen, thereby forming a triple bond in a carbon monoxide molecule.