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 the areas of electron density for each bond. Label the σ bond and the π bond.

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

Table 5.1.

Bond length and bond energies can be used to compare the reactivity of covalent molecules. 

Compare the reactivity of hydrogen halides using the information 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.

You should refer to the van der Waals' forces found in each substance in your answer.

[4]

This question is about hybridisation.

Consider the molecule shown below in Fig. 2.1.

Fig. 2.1

Identify the number of sigma and pi bonds in this molecule.

A molecule of ethanol is shown below in Fig. 2.2.

Fig. 2.2

Deduce the hybridisation of the carbon atom marked in the diagram below.

A different alcohol, methanol, bonds in a similar way to ethanol. Draw a sketch to show the orbital overlap in methanol. In your sketch include any lone pairs that are present.

Explain how the concept of hybridisation can be used to explain the triple bond present in propyne.

Consider the molecule in Fig. 3.1 which contains both sigma and pi bonds.

Fig. 3.1

 State the number of carbon atoms that exhibit sp² hybridisation.

Table 3.1 shows three different compounds containing nitrogen. Deduce the hybridisation shown by the nitrogen atoms in these molecules.

Table 3.1

Phosphorus reacts with chlorine to form PCl₅.

i) State the shape of a molecule of PCl₅  and give two different bond angles within a molecule of PCl₅.

[2]

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

[2]

PCl₅ is an example of a compound that exists as two structures depending on the conditions.

2PCl₅ (g) [PCl₄]⁺[PCl₆]^– (s)

Draw diagrams to suggest the shapes of [PCl₄]⁺ and [PCl₆]^–.

A student suggests that the PCl₅ molecule has sp³ hybridisation. Explain why the student is not correct.

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

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.

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.