CAIE A-Level Chemistry 3.4 Covalent and Coordinate Bonding

Practise electron-pair bonding, orbital overlap and coordinate-bond formation across simple and expanded-octet species.

Exam points

define covalent bonding through attraction between two nuclei and a shared electron pair
identify coordinate bonding when both electrons in the shared pair originate from one atom
describe multiple bonds as one sigma bond plus one or two pi bonds formed by orbital overlap

Covered syllabus points

3.4.1—Covalent bonding examples 3.4.2—Sigma and pi bonds 3.4.3—Terms

[Maximum number: 1]

The strength of interaction between particles determines whether the substance is a solid, liquid or gas at room temperature.

Carbon monoxide, CO, is a gas at room temperature and pressure. It contains a coordinate bond.

Explain what is meant by coordinate bond.

[Maximum number: 3]

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

(a)

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

[ 3 ]

(i)

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

[ 2 ]

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)

(ii)

The bond energy of $P \equiv P$ is $485 \mathrm{~kJ} \mathrm{~mol}^{-1}$ . The bond energy of $N \equiv N$ is $944 \mathrm{~kJ} \mathrm{~mol}^{-1}$ . Compare the reactivity of $\mathrm{P}_{2}$ and $\mathrm{N}_{2}$ . Explain your answer.

[ 1 ]

$\mathrm{P} \equiv \mathrm{P}$ is much weaker so $\mathrm{P}_{2}$ is more reactive (than $\mathrm{N}_{2}$ )

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Covered syllabus points

3.4 Covalent bonding and coordinate (dative covalent) bonding question 1

3.4 Covalent bonding and coordinate (dative covalent) bonding question 2

Question (a)

Question (i)

Question (ii)