Group 1 Elements (Alkali Metals): Inorganic Chemistry Notes for WBJEE

Group 1 Elements (Alkali Metals)

Alkali metals are the elements in Group 1 of the periodic table:
Li, Na, K, Rb, Cs, Fr.
They are the most reactive metals, have one valence electron, and they form highly basic hydroxides and salts.

1. Simple Explanation

Element	Symbol	Electron Configuration	Oxidation State	Key Feature
Lithium	Li	1s² 2s¹	+1	Smallest, least reactive of the group
Sodium	Na	[Ne] 3s¹	+1	Most commonly encountered
Potassium	K	[Ar] 4s¹	+1	Very reactive, huge atomic radius
Rubidium	Rb	[Kr] 5s¹	+1	Similar to K, but more reactive
Caesium	Cs	[Xe] 6s¹	+1	Most reactive stable alkali metal
Francium	Fr	[Rn] 7s¹	+1	Radioactive, very little data

Why they’re reactive

One valence electron is far from the nucleus (large atomic radius).
Low ionization energy (≈ 50 kJ mol⁻¹ for Li → 496 kJ mol⁻¹ for Cs).
They readily lose that electron to form a stable +1 ion.

2. Key Points

Physical Properties

Soft, low density (except Li, which is harder).
Low melting & boiling points: Li → 180 °C, Na → 98 °C, K → 63 °C, Cs → 28 °C.
Highly reflective (except Li, which is dull).
Highly reactive with air and moisture.

Chemical Properties

Reaction	Example	Observations
With water	`M + H₂O → M⁺ + OH⁻ + H₂↑`	Exothermic, releases hydrogen gas (sometimes flammable).
With oxygen	`4M + O₂ → 2MO₂`	Forms oxides, often exothermic.
With halogens	`2M + X₂ → 2MX`	Straightforward halide formation.
With acids	`M + HA → M⁺ + A⁻ + H₂↑`	Produces metal salt & hydrogen gas.
With non‑metals (C, S, P)	`M + C → MC` etc.	Forms covalent or ionic compounds.

Common Compounds

Compound	Formula	State	Uses
Hydroxide	`MOH`	Strong base	Cleaning, soap making
Oxide	`MO`	Basic oxide	Cement, refractories
Halide	`MX`	Salts	Food seasoning, optics
Carbonate	`M₂CO₃`	Basic	Fire retardants, glass
Nitrate	`MN₃O₈`	Salts	Explosives, fertilizers

Applications

Li – batteries, aerospace alloys.
Na – salt, soap, NaCl for food.
K – fertilizers (potash), glass.
Rb, Cs – atomic clocks, lasers, research.
Fr – largely theoretical, used in nuclear studies.

Safety & Handling

Store under oil to prevent reaction with air.
Avoid contact with water – can ignite.
Protective gear: gloves, goggles, lab coat.
Use in fume hood when reacting with strong acids or oxidizers.
Fr is highly radioactive; handled only by specialized labs.

3. Worked Example

Reaction of Sodium with Water

Equation
2 Na (s) + 2 H₂O (l) → 2 NaOH (aq) + H₂ (g)

Step‑by‑Step Balancing

Step	Reaction	Balance
1	Write skeleton	`Na + H₂O → NaOH + H₂`
2	Count atoms	Na 1, H 2+2=4, O 1
3	Balance Na	`2 Na + H₂O → 2 NaOH + H₂`
4	Balance H	`2 Na + 2 H₂O → 2 NaOH + H₂`
5	Balance O (already balanced)	Final equation

Observations

Heat: Reaction is exothermic (~ 400 kJ mol⁻¹).
**Hydrogen gas