p‑Block Elements (Groups 13‑18)
Audience: SRMJEEE aspirants
Format: Markdown study notes – simple explanation → key points → worked example → revision summary
1. Simple Explanation
The p‑block of the periodic table contains elements whose outermost electron is in a p‑orbital (ns²npⁿ).
- Groups 13–18 are the p‑block (except the two s‑block groups 1 & 2).
- They include metals, metalloids, non‑metals, and noble gases.
- Elements in the same group share similar valence‑electron configurations, leading to comparable chemical behaviour, though exceptions (e.g., Ga, In, Tl) exist.
2. Key Points
| Group | Representative Elements | General Electronic Config. | Typical Oxidation State(s) | Common Compounds & Uses |
|---|---|---|---|---|
| 13 | B, Al, Ga, In, Tl | ns²np¹ | +3 (rare +1 for Tl) | Oxides (Al₂O₃), Halides (AlCl₃); Al used in alloys, Ga in semiconductors |
| 14 | C, Si, Ge, Sn, Pb | ns²np² | +4, +2 (Sn, Pb also +4) | Carbon allotropes, SiO₂ (sand), Ge compounds, SnO₂ (catalyst) |
| 15 | N, P, As, Sb, Bi | ns²np³ | +5, +3, –3 | N₂, NO₃⁻, H₃PO₄, As₂O₅, Sb₂S₃, Bi₂O₃ (catalyst) |
| 16 | O, S, Se, Te, Po | ns²np⁴ | –2, +6, +4, +2 | H₂O, SO₂, H₂S, SeO₃²⁻, TeO₂ (catalyst) |
| 17 | F, Cl, Br, I, At | ns²np⁵ | –1 | HF, HCl, HBr, HI, halides (NaF, NaCl) |
| 18 | He, Ne, Ar, Kr, Xe, Rn | ns²np⁶ | 0 | Inert gases; Kr, Xe used in lighting, Rn in radon therapy (limited) |
General Trends (down a group)
| Property | Trend |
|---|---|
| Atomic radius | Increases |
| Electronegativity | Decreases |
| First ionization energy | Decreases |
| Electronegativity of halides | Decreases (e.g., HF > HCl) |
| Oxidizing strength | Decreases (O₂ > SO₃ > SeO₃) |
Notable Exceptions & Anomalies
| Element | Reason | Observation |
|---|---|---|
| Ga, In, Tl | Poor metal‑metal bonding, high affinity for nitrogen | Form amphoteric oxides & hydroxides (e.g., Ga(OH)₃, Tl(OH)₃) |
| Bi | Heavy element, strong spin‑orbit coupling | Exhibits +3 and +5; +3 is more stable |
| F | Highest electronegativity, strong oxidizer | HF is weak acid; F₂ is very reactive |
| Oxygen | Forms peroxides, superoxides, ozonides | O₂⁻, O₂²⁻, O₃ |
Important Reactions
| Reaction | p‑Block Compound | Notes |
|---|---|---|
| Halogenation | Cl₂ + 2Na → 2NaCl | Sodium reacts violently with halogens |
| Oxidation | 4Cl₂ + 10NaOH → 4NaClO₃ + 6NaCl + 5H₂O | Chlorine oxidizes to chlorate |
| Formation of acids | N₂ + 3H₂ → 2NH₃; NH₃ + H₂O → NH₄OH | Ammonia base to ammonium hydroxide |
| Metal extraction | 2AlCl₃ + 6Na → 2Al + 6NaCl | Electrolysis of molten AlCl₃ |
3. Worked Example
Problem:
A student wants to prepare a salt by reacting gallium(III) oxide (Ga₂O₃) with sodium hydroxide.
- Write the balanced equation.
- Identify the product’s chemical formula.
- State the oxidation state of Ga in the product.