Which statement about nitrogen molecules and ethene molecules is correct?
A) A nitrogen molecule has 2 more shared electrons than an ethene molecule.
B) An ethene molecule has 3 more shared electrons than a nitrogen molecule.
C) A nitrogen molecule has 4 more shared electrons than an ethene molecule.
D) An ethene molecule has 6 more shared electrons than a nitrogen molecule.
▶️ Answer/Explanation
Ans: D
First, let’s determine the number of shared electrons in each molecule:
1. Nitrogen molecule (N₂): Triple bond between two nitrogen atoms (N≡N), which involves 6 shared electrons (3 pairs).
2. Ethene molecule (C₂H₄): Double bond between carbon atoms (4 shared electrons) plus 4 single C-H bonds (4 × 2 = 8 shared electrons). Total = 12 shared electrons.
Difference: Ethene (12) – Nitrogen (6) = 6 more shared electrons in ethene.
Therefore, option D is correct – an ethene molecule has 6 more shared electrons than a nitrogen molecule.
Sulfur is a simple molecule with the formula \( S_8 \).
Which row describes and explains the melting point of sulfur?
| melting point | explanation | |
|---|---|---|
| A | high | the covalent bonds between sulfur atoms are strong |
| B | high | the covalent bonds between sulfur molecules are strong |
| C | low | the forces of attraction between sulfur atoms are weak |
| D | low | the forces of attraction between sulfur molecules are weak |
▶️ Answer/Explanation
Ans: D
Sulfur (\( S_8 \)) exists as simple molecular structures. The covalent bonds within each \( S_8 \) molecule are strong, but the intermolecular forces (van der Waals forces) between different \( S_8 \) molecules are weak. This explains why sulfur has a relatively low melting point – it doesn’t take much energy to overcome these weak intermolecular forces.
Option A is incorrect because while the covalent bonds within molecules are strong, they don’t break during melting. Option B is wrong because there are no covalent bonds between molecules. Option C is incorrect because it refers to forces between atoms within molecules rather than between molecules.
Which diagram shows the covalent bonding in a molecule of carbon dioxide?
A) O–C–O
B) O=C–O
C) O=C=O
D) O≡C≡O
▶️ Answer/Explanation
Ans: C
Carbon dioxide (CO₂) has a linear molecular geometry with double bonds between the carbon atom and each oxygen atom. Each oxygen shares two pairs of electrons with the central carbon atom, forming two double bonds (O=C=O).
Option A shows single bonds which is incorrect. Option B shows one double and one single bond which doesn’t represent CO₂’s symmetrical structure. Option D shows a triple bond which doesn’t occur in CO₂.
The bonding, structure and melting point of sodium chloride and sulfur dichloride are shown.
| compound | bonding | structure | melting point / °C |
|---|---|---|---|
| sodium chloride | ionic | giant lattice | 801 |
| sulfur dichloride | covalent | simple molecular | -121 |
Why does sulfur dichloride have a lower melting point than sodium chloride?
A) The covalent bonds in sulfur dichloride are weaker than the attractive forces between molecules in sodium chloride.
B) The covalent bonds in sulfur dichloride are weaker than the ionic bonds in sodium chloride.
C) The attractive forces between molecules in sulfur dichloride are weaker than the attractive forces between molecules in sodium chloride.
D) The attractive forces between molecules in sulfur dichloride are weaker than the ionic bonds in sodium chloride.
▶️ Answer/Explanation
Ans: D
Sulfur dichloride (SCl₂) is a simple covalent molecule with weak intermolecular forces (van der Waals forces) between molecules, while sodium chloride (NaCl) has a giant ionic lattice structure with strong electrostatic forces between ions.
The key difference is that melting NaCl requires breaking strong ionic bonds, while melting SCl₂ only requires overcoming weak intermolecular forces. The covalent bonds within SCl₂ molecules aren’t broken during melting, making options A and B incorrect. Option C is wrong because NaCl doesn’t have molecules with intermolecular forces – it has an ionic lattice.