1.4 Covalent Bonding

A hydrogen atom is 0.074 nm, or 0.00000000074 m long.

Write 0.00000000074 m in standard form.

Caesium atoms are 0.267 nm long.

State how many orders of magnitude exist between the length of a hydrogen atom and the length of a caesium atom.

Hydrogen exists as molecules.

Draw a dot-cross diagram for a hydrogen molecule.

Hydrogen molecules are the smallest molecules.

Explain why.

Figure 1 shows a dot-cross diagram and structure of a methane molecule.

                                             Dot-cross diagram                                                                      Structure

Figure 1

Name the type of bond formed when two atoms share a pair of electrons.

Complete Figure 2 to show the dot cross diagram of a carbon dioxide molecule.

Figure 2

Draw the structure of a carbon dioxide molecule.

The boiling point of methane is -162°C.
The boiling point of carbon dioxide is -75°C.

A student concludes that this difference is due to the number of bonds between the atoms in each molecule.

Discuss if you think this conclusion is correct.

An ethene molecule contains carbon and hydrogen atoms.
Its formula is C₂H₄.

Complete the dot and cross diagram of ethene, shown in Figure 1.

Figure 1

Complete Figure 2 to show the structure of ethene.

Use a single line to show each covalent bond.

Figure 2

Give an advantage of using Figure 3 rather than Figure 4 to represent ethene.

Higher Tier Only

Table 1 shows the bond energies for a single and double carbon bond.

Table 1

Describe and explain the difference between the bond energies.

A nitrogen molecule has the formula N₂.

Nitrogen molecules are diatomic.
Suggest what this means.

Nitrogen atoms have the electronic configuration 2.8.5.

Draw a dot and cross diagram to show the covalent bonding in a nitrogen molecule.

Show only the electrons in the outer shell.

Use your knowledge of bonding to explain why nitrogen is a gas at room temperature.

Nitrogen is an unreactive gas.

Suggest why.

Covalent substances can be simple molecular covalent or giant covalent.

Oxygen, O₂, is also a simple molecular, covalent substance.

Draw a dot and cross diagram for the molecule of oxygen.

Figure 8 shows the arrangement of carbon atoms in diamond, graphene and a fullerene (C₆₀).

Consider these three substances.

Explain, in terms of their structures and bonding, their relative melting points, strengths and abilities to conduct electricity.

Which statement is not true about covalent bonding? 

What are the typical sizes, in orders of magnitude, of atoms and small molecules? 

Iodine and bromine are both halogens. The bonding in iodine is similar to the bonding in bromine.

Suggest two reasons why they bond in similar ways.

Complete the diagram below to show the bonding arrangement in a molecule of iodine.

Show the outer shell electrons only.

Explain why liquid iodine is unable to conduct electricity.

Iodine has an atomic number of 53 and xenon has an atomic number of 54. Explain why xenon exists as an atom where as iodine exists as a molecule.