Answer

• As you go down the group, the atoms have more electrons.
• Larger molecules with more electrons have larger temporary and larger induced dipoles.
• This results in stronger electrostatic attractions between the partially positive and partially negative parts of the molecules (stronger Van Der Waals forces).

Answer

• H₂O hydrogen bonds whereas the other molecules do not.
• More energy is needed to break the hydrogen bond than is needed to overcome the induced dipole interactions in the other four molecules.
• The increase from H₂S to H₂Po is due to the atoms getting larger with more electrons as you go down the group.
• This results in stronger induced dipoles, which results in higher boiling points.

Answer

• Na: Metallic bonding.
• Mg: Metallic bonding with stronger force of attraction between the ions in the lattice and the delocalised electrons because the ions are 2+.
• Al: Metallic bonding with stronger force of attraction between the ions in the lattice and the delocalised electrons because the ions are 3+.
• Si: Giant covalent structure with many strong covalent bonds.
• P: Phosphorus is a P₄ molecule. It has weak Van Der Waals forces.
• S: Sulfur is S₈. Its Van Der Waals forces are stronger because the molecule is larger with more electrons.
• Cl: Chlorine is Cl₂. Its Van Der Waals forces are weaker than S₈ and P₄ because it is a smaller molecule with fewer electrons.
• Ar: Argon is monatomic. It is the smallest with the least electrons, so its Van Der Waals forces are the weakest.