Question

How many sigma bonds and pi bonds are there in ${\mathrm{C}}_2$(the carbon molecule)?

Answer 1

Sigma and pi bonds:

1. The sigma bond is the strongest covalent link formed by the head-on overlapping atomic orbitals.
2. They can be found in alkanes, alkenes, and alkynes.
3. A double bond consists of one sigma and one pi link.
4. Pi bonds are covalent chemical bonds that involve the lateral overlapping of two lobes of one atomic orbital with two lobes of another atomic orbital from a different atom.
5. Due to the lower level of overlapping, it is a weak bond.

Carbon molecule:

1. Configuration of the ${\mathrm{C}}_2$ molecule $=\mathrm{\sigma }1{\mathrm{s}}^2{\mathrm{\sigma }}^{*}1{\mathrm{s}}^2\mathrm{\sigma }2{\mathrm{s}}^2{\mathrm{\sigma }}^{*}2{\mathrm{s}}^2\mathrm{\pi }2{{\mathrm{p}}_{\mathrm{x}}}^2\mathrm{\pi }2{{\mathrm{p}}_{\mathrm{y}}}^2$
2. Therefore bond order$=\frac{\mathrm{Number}\mathrm{of}\mathrm{bonding}\mathrm{electron}-\mathrm{number}\mathrm{of}\mathrm{antibonding}\mathrm{electron}}{2}\Rightarrow \frac{8-4}{2}\Rightarrow 2$
3. The last two paired sets of electrons enter the degenerate (identical energy) pi-bonding set of orbitals, i.e. $\mathrm{\pi }2{\mathrm{p}}_{\mathrm{x}}$ and$\mathrm{\pi }2{\mathrm{p}}_{\mathrm{y}}$, according to Molecular Orbital theory.
4. Because these four electrons are in the pi orbitals, the ${\mathrm{C}}_2$ molecule's two bonds will be pi bonds alone, with no sigma bonds.

Therefore, there are $2\mathrm{\pi }$ bonds present in the ${\mathrm{C}}_2$ molecule.