DP IB Chemistry: HL - Oxides, Group 1 & Group 17

3.2.1 Periodic Trends: Oxides Across a Period

Oxides

• Oxides across a period show a transition from basic to amphoteric to acidic character.
• Aluminium oxide is amphoteric: reacts as both an acid and a base.
• The acidic and basic nature of Period 3 oxides is influenced by structure, bonding, and electronegativity.
• Electronegativity differences lead to different types of bonding:
  • Ionic bonds in oxides of Na, Mg, and Al due to large electronegativity differences.
  • Covalent bonds in oxides of Si, P, and S due to electron sharing.

Reactions with Water

• Metallic oxides react with water to form hydroxides (basic solutions).
• Non-metallic oxides form acidic solutions (oxoacids) when reacting with water.

Making Predictions

• Position in the periodic table helps predict metallic/non-metallic behavior.
• Metal oxides become more ionic down a group and less ionic across a period.
• Non-metal oxides like S, N, and P form molecular covalent compounds.
• Example: Na₂O produces a higher pH than CaO when added to water.

3.2.2 Periodic Trends: Group 1 - The Alkali Metals

Alkali Metals

• Group 1 metals: lithium, sodium, potassium, rubidium, cesium, and francium.
• Characteristics:
  • Soft, low melting points, low densities.
  • React vigorously with water to form alkaline solutions.
• Reaction with water produces alkaline metal hydroxides and hydrogen gas.
• Alkali metals react vigorously with halogens to form metal halide salts.
• Reactivity increases down the group due to larger atomic size and shielding.

3.2.3 Periodic Trends: Group 17 - The Halogens

Halogens

• Group 17 non-metals: fluorine, chlorine, bromine, iodine, and astatine.
• Diatomic molecules with seven electrons in the outer shell, forming halide ions.
• Physical properties:
  • Melting and boiling points increase down the group.
  • Reactivity decreases down the group due to decreased electron affinity and increased atomic radius.

Displacement Reactions

• More reactive halogens displace less reactive ones from halide solutions.
• Reactivity increases up the group (e.g., Chlorine displaces bromine and iodine).
• Example reactions:
  • Chlorine displaces bromine from potassium bromide solution.
  • Bromine displaces iodine from sodium iodide solution.

Practice and Application

• Understanding trends and applying them to predict reactions and outcomes.
• Example questions provided to test knowledge and application of concepts.