Introduction to P-Block Elements

Overview

This lecture focuses on the main concepts of P-block elements, their physical/chemical properties, oxidation states, inert pair effect, and characteristics of various groups (13 to 18).

General Information of P-Block

• The last electron enters the p-subshell in the P-block.
• General electronic configuration: ns2 np1-6 (except helium).
• Group 13: ns2 np1, Group 14: ns2 np2, ..., Group 18: ns2 np6.
• Electronic configuration of helium: 1s2.

Inert Pair Effect

• In heavier elements below, poor shielding by d and f electrons increases the effective nuclear charge (Z-effective).
• Reactivity of ns electrons decreases, increasing the stability of the lower oxidation state.
• In Groups 13, 14, 15, the higher oxidation state is more stable at the top, and the lower oxidation state is more stable at the bottom.
• Thallium(I), Lead(II), Bismuth(III), etc., are more stable in the lower oxidation state.

True/False and Examples

• PbO2, Pb2O3, PbO4 are all oxidizing agents (true).
• PbI4 does not exist; Sn+2 is a reducing agent; SO2 is a reducing agent; TeO2 is an oxidizing agent.
• In Group 14 dihalides (like PbX2), the +2 oxidation state is more stable.

Physical Properties Trends

• Atomic size generally increases from top to bottom, with contraction in some groups (e.g., Ga).
• Ionization energy, electronegativity, and density decrease from top to bottom.
• For melting/boiling points order, remember the trick: 1-max, 5-min, group-wise trends.
• Electronegativity decreases in groups 15, 16, 17.

Chemical Reactivity (Group-wise)

• Group 13 oxides: boron - acidic; Al, Ga - amphoteric; lower ones - basic.
• Group 14 oxides: CO - neutral, others acidic, Sn/Pb amphoteric.
• Group 15 oxides: N, P acidic; As, Sb amphoteric; Bi basic.
• Group 16 oxides: SO2, TeO2 change from reducing to oxidizing nature from top to bottom.
• Group 17: Acidity of hydrides increases from top to bottom; bond angle decreases in 15-16.

Group 18 (Noble Gases)

• All noble gases are monoatomic, colorless, odorless, sparingly soluble, and very unreactive.
• Helium is the most ideal gas; real character increases downwards.
• Xe was the first to form a compound (Xe+PtF6) (Neil Bartlett).

Anomalous Behavior (Elements of the Second Period)

• Boron, carbon, nitrogen, oxygen, fluorine do not show covalency more than 4.
• They can only form pπ-pπ bonds; Dπ-bonds do not form.
• Anomalous behavior occurs in lower members due to high electronegativity, high ionization energy, etc.

Key Terms & Definitions

• P-block — The group in which the last electron enters the p-shell.
• Inert Pair Effect — The decreased reactivity of ns electrons in heavy elements.
• Oxidation State — The number of electrons lost or gained by an atom of an element.
• Amphoteric Oxide — An oxide that reacts with both acids and bases.
• Catenation — The formation of long chains of atoms of the same element.

Action Items / Next Steps

• Revise NCERT P-block (class 11/12) charts, trends, and examples.
• Quick revision of anomalous behavior, physical-chemical trends from notes.
• Pay special attention to important reactions and the nature of oxides.