MHT-CET Chemistry · Elements of Group 1 and 2

Group 1: The Alkali Metals — Properties, Oxides and Uses

The alkali metals Li, Na, K, Rb and Cs have one valence electron, form +1 ions with a noble-gas configuration, are the most electropositive elements, and become softer, lower-melting and more reactive down the group.

All Elements of Group 1 and 2 notes MHT-CET Chemistry strategy

Why this matters

11 PYQs, all EASY. Six test the group's properties — which statement is false, which metal tarnishes, what +1 ions are like; five test oxides, carbonate decomposition, the blue solution in ammonia, and caesium's use. Two cards.

Concept 1 of 2: Properties of the Alkali Metals

One loosely held s-electron explains the whole group: the metals lose it easily (most electropositive, strongly negative E°), the resulting M⁺ ion has a closed shell (colourless, diamagnetic compounds), and metallic bonding weakens as the atoms grow, so melting points FALL down the group.

Definition

Group 1: Li, Na, K, Rb, Cs, Fr. Be, Mg, Sr are group 2 — not alkali metals.
Oxidation state +1 only; M⁺ has a noble-gas configuration → colourless, diamagnetic compounds.
Most electropositive elements; large negative E°.
Melting point decreases down the group; density: K < Na (the one exception to the rising trend).
Silvery white, soft, and tarnish rapidly in air — potassium within seconds.

Statement	True or false
All alkali metals are silvery white	True
Density of K is less than Na	True
Compounds of M⁺ are diamagnetic (and colourless)	TrueQ
Melting point increases down the group	False — it decreasesQ
They are the most electropositive elements	TrueQ
They form dipositive ions	False — +1 only

Practice this conceptself-check · 2 quick reps

The same idea in a real exam question:

MHT-CET · 2024 · 9th May Shift 1 · Q83Easy

Example 1 · Elements of Group 1 and 2 · Group 1 Alkali Metals, Properties and Reactivity

Which from following statements is NOT correct?

Calling M⁺ compounds paramagnetic

A +1 alkali-metal ion has no unpaired electrons, so its compounds are diamagnetic and colourless. 'Paramagnetic' is the false statement the paper plants.

Drill 5 more on properties of the alkali metals

Concept 2 of 2: Oxides, Carbonates, Ammonia Solutions and Uses

Burned in excess oxygen, each metal makes the oxide its cation can best stabilise: tiny Li⁺ a normal oxide, Na⁺ a peroxide, the big K⁺, Rb⁺, Cs⁺ superoxides. Li⁺ is also small enough to pull apart a carbonate, so only Li₂CO₃ decomposes on heating.

Definition

Oxides in excess O₂: Li → Li₂O; Na → Na₂O₂ (peroxide); K, Rb, Cs → KO₂ (superoxide).
Li₂CO₃ → Li₂O + CO₂ on heating; the other group-1 carbonates are stable.
In liquid ammonia: deep blue solution (ammoniated electrons), bronze when concentrated.
Uses: Cs in photoelectric cells (lowest ionisation enthalpy); Li in batteries; Na in sodium lamps.

Metal	Oxide with excess O₂	Note
Li	Li₂O (normal oxide)	Li₂CO₃ decomposes: Li₂O + CO₂Q
Na	Na₂O₂ (peroxide)	Q
K, Rb, Cs	KO₂ (superoxide)	Cs used in photoelectric cellsQ

Practice this conceptself-check · 2 quick reps

The same idea in a real exam question:

MHT-CET · 2025 · 21 April Shift II · Q91Easy

Example 2 · Elements of Group 1 and 2 · Group 1 Alkali Metals, Properties and Reactivity

Which from following elements form superoxide with air?

Drill 4 more on oxides, carbonates, ammonia solutions and uses

Summary — formulas & gotchas at a glance

A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.

Reference tables (2)

Properties of the Alkali Metals6 rows

Statement	True or false
All alkali metals are silvery white	True
Density of K is less than Na	True
Compounds of M⁺ are diamagnetic (and colourless)	TrueQ
Melting point increases down the group	False — it decreasesQ
They are the most electropositive elements	TrueQ
They form dipositive ions	False — +1 only

Oxides, Carbonates, Ammonia Solutions and Uses3 rows

Metal	Oxide with excess O₂	Note
Li	Li₂O (normal oxide)	Li₂CO₃ decomposes: Li₂O + CO₂Q
Na	Na₂O₂ (peroxide)	Q
K, Rb, Cs	KO₂ (superoxide)	Cs used in photoelectric cellsQ

Watch out for (1)

Calling M⁺ compounds paramagnetic
→ Properties of the Alkali Metals

Test yourself on Elements of Group 1 and 2

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