Question 1: Define a simple molecule in terms of covalent bonding.

Answer: A molecule formed when two or more non-metal atoms are joined by covalent bonds, sharing electrons.

Question 2: Explain why simple molecules tend to have low melting and boiling points.

Answer: Because the intermolecular forces between simple molecules are weak, requiring less energy to break.

Question 3: Describe the general structure of a simple covalent molecule.

Answer: They consist of non-metal atoms linked by covalent bonds, often forming discrete molecules with specific shapes.

Question 1: Calculate the molecular formula of water given that its molecular mass is approximately 18 u, with hydrogen having an atomic mass of 1 u and oxygen 16 u.

Answer: H2O

Question 2: A sample of methane (CH4) has a mass of 16 g. Calculate the number of moles in this sample. (Atomic masses: C=12 g/mol, H=1 g/mol)

Answer: 1 mol

Question 1: Describe a safe method to test for the presence of hydrogen gas in a laboratory setting.

Answer: Hold a lit splint at the mouth of the test tube; if hydrogen is present, it will produce a squeaky pop sound.

Question 2: Identify two variables that must be controlled when measuring the boiling point of a simple molecule.

Answer: Pressure and purity of the sample.

Question 1: A sample of ammonia (NH3) has a boiling point of -33.3°C. Explain how intermolecular forces influence this boiling point compared to water.

Answer: Ammonia has weaker hydrogen bonds than water, leading to a lower boiling point due to weaker intermolecular forces.

Question 1: Explain why molecules like nitrogen (N2) and oxygen (O2) are gases at room temperature despite having strong covalent bonds. Include in your answer the nature of intermolecular forces and molecular structure. (6 marks)

Answer: Nitrogen and oxygen are diatomic molecules with non-polar covalent bonds. They are held together by weak London dispersion forces, which are much weaker than covalent bonds. As a result, these molecules require less energy to overcome intermolecular forces, making them gases at room temperature despite strong covalent bonds within the molecules.

Question 1: Describe a practical application of simple covalent molecules in industry or daily life.

Answer: Methane (CH4) is used as a fuel for heating and cooking because it is a clean-burning simple molecule with a high energy content.