CAIE A-Level Chemistry 3.4.2 Sigma and Pi Bonds

Practise identifying direct and sideways orbital overlap and counting sigma and pi bonds in molecules.

Exam points

describe a sigma bond as direct overlap along the internuclear axis
describe a pi bond as sideways overlap of adjacent p orbitals above and below the sigma framework
count a single bond as sigma, a double as one sigma plus one pi and a triple as one sigma plus two pi

[Maximum number: 2]

Nitrogen and phosphorus are elements in Group 15 of the Periodic Table.

At very high temperatures, phosphorus can form $\mathrm{P}_{2}$ molecules.
$\mathrm{P}_{2}$ contains a triple bond, $\mathrm{P} \equiv \mathrm{P}$ .

Describe the formation of the $\mathrm{P} \equiv \mathrm{P}$ bond in terms of orbital overlap.

M1 one sigma / $\sigma$ bond AND head-on (overlap of) p / sp (orbitals)

M2 two pi / $\pi$ bond(s) AND side-on (overlap of / involving) p (orbitals)

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