Revision: Some P-block Elements Chemistry Science (English Medium) Class 11 CBSE

When an element possess 2 or more different forms in the same state, they are called allotropes and the phenomenon is known as allotropy. Diamond and graphite are the 2 allotropes of carbon.

When an element possess 2 or more different forms in the same state, they are called allotropes and the phenomenon is known as allotropy. Diamond and graphite are the 2 allotropes of carbon.

General electronic configuration: ns² np¹.

• All group 13 elements predominantly show a +3 oxidation state.
• Aluminium is the third most abundant element in Earth's crust (after oxygen and silicon).
• Boron is non-metallic; it does not react with non-oxidising acids but dissolves in strong oxidising acids like HNO₃ (conc.) and H₂SO₄ (conc.).

Trends in Physical Properties:

Trends in Chemical Properties:

• Group 13 elements are less reactive than Group 1 and 2 elements.
• All Group 13 elements form ionic compounds except boron, which forms covalent compounds.
• Reaction with oxygen: Boron forms a mixture of oxide (B₂O₃) and nitride (BN) when heated at 700°C in air. Oxygen has no effect on aluminium in normal conditions, but in moist air, a thin protective oxide layer forms on its surface.
• Reaction with water: Except for boron, Group 13 elements decompose in boiling water to produce hydrogen gas. Example: 2Al + 6H₂O → 2Al(OH)₃ + 3H₂↑
• Reaction with halogens: All Group 13 elements react with halogens to form trihalides (MX₃), except thallium (which prefers monohalides due to the inert pair effect).

Anomalous Properties of Boron:

Boron behaves differently from the rest of Group 13 because of:

• Small size – high polarising power
• High ionisation energy – does not form B³⁺ ions easily
• High electronegativity
• Absence of vacant d-orbitals – cannot expand its coordination number beyond 4

General electronic configuration: ns² np²

• Size & Energy Trends: Down the group, atomic and ionic radii increase, while ionisation energy decreases.
• Oxidation States: Show +4 and +2 states → +4 stable at top (C, Si), +2 becomes stable down the group (Sn, Pb) due to inert pair effect.
• Metallic Character: Increases down the group → C is non-metal, Si/Ge metalloids, Sn/Pb metals.
• Covalent Nature: Tendency to form covalent compounds decreases down the group as metallic character increases.
• Anomalous Behaviour of Carbon: Due to small size, high electronegativity, absence of d-orbitals, and high catenation.
• Catenation & Bonding: Carbon shows maximum catenation and strong covalent bonding, forming chains and rings.

Allotropes of Carbon:

• Crystalline: Diamond (hardest), Graphite (conducts electricity), Fullerene (spherical)
• Amorphous: Coke, Charcoal (adsorbent), Lampblack (~98–99% carbon)