Intermolecular Forces, Electronegativity & Bond Properties (CIE AS Chemistry)

Ammonia, NH₃, and methane, CH₄, are the hydrides of elements which are next to one another in the Periodic Table.

In the boxes below, draw the ‘dot-and-cross’ diagram of a molecule of each of these compounds.

Show outer electrons only.

State the shape of each molecule.

Ammonia is polar whereas methane is non-polar. The physical properties of the two compounds are different.

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State one physical property of ammonia which is caused by its polarity.

When ammonia gas is mixed with hydrogen chloride, white, solid ammonium chloride is formed.

State each type of bond that is present in one formula unit of ammonium chloride and how many of each type are present.

You may draw diagrams.

The structural formulae of water, methanol and methoxymethane, CH₃OCH₃, are given below. 

The physical properties of a covalent compound, such as its melting point, boiling point, vapour pressure, or solubility, are related to the strength of attractive forces between the molecules of that compound.

These relatively weak attractive forces are called intermolecular forces. They differ in their strength and include the following.

By using the letters A, B, or C, state the strongest intermolecular force present in each of the following compounds.

For each compound, write the answer on the dotted line:

Methanol and water are completely soluble in each other.

When equal volumes of ethoxyethane, C₂H₅OC₂H₅, and water are mixed, shaken, and then allowed to stand, two layers are formed.

Suggest why ethoxyethane does not fully dissolve in water. Explain your answer.

Based on the type of intermolecular force present, explain why butan-1-ol has a higher boiling point than butanal.

Ethane, C₂H₆, and disilane, Si₂H₆, are both hydrides of Group 4 elements with similar structures but different chemical properties.

Explain why disilane has a higher boiling point than ethane.

Based on the type of intermolecular force present, explain the difference in solubility in water between ethane and ethanol.

Paperclips have a higher density than water. However, if a paperclip is lowered carefully onto the surface of water, the paperclip can float. When a drop of liquid soap is added to the water, the paperclip sinks.

Suggest explanations for these observations.

Ammonia is highly soluble in water. Draw diagrams to show the two ways that intermolecular forces can form between a molecule of water and a molecule of ammonia to explain this.

NH₃, HCl and F₂ all exist as gases at room temperature and pressure.

NH₃ has the highest boiling point of -33 °C .

Predict whether HCl or F₂ has the lowest boiling point and explain why there is a difference between their boiling points.