Covalent Bonding & Coordinate (Dative Covalent) Bonding (Cambridge (CIE) AS Chemistry): Exam Questions

Alkenes contain a carbon to carbon double bond that consists of a σ bond and a π bond.

Complete the diagram to show, in terms of orbital overlap, how the σ bond and the π bond are formed in a C=C double bond. Label each bond.

Use the data in Table 5.1 to explain why ethene contains stronger covalent bonds between carbon atoms than ethane.

Table 5.1

Describe and explain the relative thermal stabilities of HCl, HBr and HI, using the data in Table 5.2.

Table 5.2

The boiling points of the hydrogen halides are shown in Table 5.3.

Table 5.3

i) Explain why hydrogen halides have relatively low boiling points despite having strong covalent bonds.

[2]

ii) Explain why HF has a higher boiling point than HCl.

[4]

The structure of a molecule is shown in Fig. 2.1.

Fig. 2.1

State the number of σ bonds and π bonds in one molecule of this compound.

Fig. 2.2 shows the structure of ethanol.

Fig. 2.2

State the hybridisation of the carbon atom marked in Fig. 2.2.

Sketch a labelled diagram to show, in terms of orbital overlap, how the bonds are formed in methanol, CH₃OH. Your diagram should include any lone pairs of electrons.

Describe how the carbon-carbon triple bond forms in propyne, CH₃C≡CH. Refer to orbital overlap and hybridisation in your answer.

Fig. 3.1 shows the structure of an organic molecule.

Fig. 3.1

State the number of carbon atoms that are sp² hybridised in this molecule.

Table 3.1 shows three nitrogen-containing species. Complete Table 3.1 to state the hybridisation of the nitrogen atom in each species.

Table 3.1

Phosphorus reacts with chlorine to form PCl₅.

i) State the shape of, and two different bond angles in, a molecule of PCl₅.

[2]

ii) Draw a dot-and-cross diagram to show the bonding in a molecule of PCl₅. Show the outer electrons only.

[2]

In the solid state, phosphorus(V) chloride exists as an ionic lattice containing [PCl₄]⁺ and [PCl₆]^– ions.

Draw three-dimensional diagrams to show the shapes of the [PCl₄]⁺ and [PCl₆]^– ions.

A student suggests that the PCl₅ molecule has sp³ hybridisation. Explain why the student is incorrect.

Antimony(V) chloride is another Group 15 chloride. Under standard conditions, it is a liquid made from SbCl₅ molecules.

Use your answer to (b) to explain why phosphorus(V) chloride, in its solid form, has a higher melting point than antimony(V) chloride.

Under the right conditions, molecules of SbCl₅ join together to form Sb₂Cl₁₀.

Complete Fig. 4.1 to show the bonding in Sb₂Cl₁₀. Include the coordinate (dative covalent) bonds.

Fig. 4.1

The other Group 15 elements also form pentachlorides with the exception of nitrogen.

Suggest a reason why nitrogen does not form NCl₅.