Inorganic Chemistry: Periodic Trends and Main-Group Elements
What you must know
Master the trends - atomic radius, ionisation energy, electron affinity, electronegativity, metallic character - and their anomalies. Know the chemistry of the main groups: alkali and alkaline-earth metals (reactivity with water, oxides, hydroxides), group 13–14 elements (amphoteric behaviour of Al and its oxide), group 15–16 (nitrogen fixation, ammonia, nitric and sulfuric acid industrial routes, SO₂ as a reducing agent), and the halogens and noble gases (displacement reactions, oxidising power falling down the group). Understand why fluorine is exceptional and why noble gases are largely inert.
Traps
- Assuming all group 2 hydroxides are equally soluble; solubility increases down the group.
- Forgetting that Al₂O₃ and Al(OH)₃ are amphoteric, dissolving in both acid and base.
- Mixing up oxidising strength of halogens (F₂ strongest, I₂ weakest) with reducing strength of halides (I⁻ strongest).
- Overlooking that nitrogen is unreactive because of the strong N≡N triple bond.
Worked example
Compare oxidising power of Cl₂ and I₂. Chlorine displaces iodine from potassium iodide: Cl₂ + 2KI → 2KCl + I₂. The reaction proceeds because Cl₂ has the greater tendency to gain electrons (higher reduction potential); iodine cannot displace chloride. Rule of thumb: down group 17, oxidising power decreases and halide reducing power increases.