Revision: Class 11 >> Some p-Block elements NEET (UG) Some p-Block elements

The compounds having this characteristic unit in their structure are called aromatic compounds.

The compounds having this characteristic unit in their structure are called aromatic compounds.

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)

• Carbon compounds can have straight, branched, or ring chains of carbon atoms.
• Isomers have the same formula but different structures (e.g., butane).
• Crude oil is a mix of hydrocarbons; fuels like LPG and petrol are separated by fractional distillation.
• Saturated hydrocarbons have single bonds, while unsaturated ones have double or triple bonds.
• Aromatic compounds, such as benzene, have rings with alternating double bonds.

• Carbon compounds can have straight, branched, or ring chains of carbon atoms.
• Isomers have the same formula but different structures (e.g., butane).
• Crude oil is a mix of hydrocarbons; fuels like LPG and petrol are separated by fractional distillation.
• Saturated hydrocarbons have single bonds, while unsaturated ones have double or triple bonds.
• Aromatic compounds, such as benzene, have rings with alternating double bonds.