Topic 3.1.3: Bonding Exam Practice

(a) PH3:

• Phosphorus has 3 bonding pairs and 1 lone pair of electrons around the central atom. [1]
• Electron pairs repel each other to get as far apart as possible. The lone pair repels more strongly than the bonding pairs, reducing the bond angle. [1]
• Shape: trigonal pyramidal. Bond angle: 107° (allow 107.0°). [1]

(b) AlCl4-:

• Aluminium has 4 bonding pairs and 0 lone pairs of electrons around the central atom. (Al has 3 outer electrons, plus 1 from the charge, sharing 4 with Cl). [1]
• The 4 bonding pairs repel each other equally to get as far apart as possible. [1]
• Shape: tetrahedral. Bond angle: 109.5°. [1]

(a)

• The power of an atom [1]
• to attract the shared pair of electrons in a covalent bond. [1]

(b)

• Oxygen is highly electronegative, so water molecules form hydrogen bonds between them. [1]
• Sulfur is less electronegative, so hydrogen sulfide molecules are held together by weaker permanent dipole-permanent dipole / London forces. [1]
• Hydrogen bonds are much stronger than dipole-dipole forces and require more thermal energy to break. [1]

(c)

• CCl4 is highly symmetrical (tetrahedral), so the individual C-Cl bond dipoles cancel each other out, leaving no overall dipole. [1]
• CHCl3 is non-symmetrical, so the dipoles do not cancel, resulting in a net dipole moment. [1]

Indicative content:

• Sodium Chloride: Giant ionic lattice structure with electrostatic attractions between oppositely charged Na+ and Cl- ions. [1]
• Graphite: Giant covalent (macromolecular) structure composed of hexagonal layers of carbon atoms, where each carbon is covalently bonded to three others. [1]
• NaCl conductivity: In the solid state, the ions are fixed in position in the lattice and cannot move. [1] When molten or dissolved in water, the giant lattice breaks, and the ions are free to move and carry charge. [1]
• Graphite conductivity: Each carbon atom has one delocalised electron (as it only forms 3 bonds). [1] These delocalised electrons are free to move along the hexagonal layers and carry electrical charge in both solid and liquid states. [1]