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Part of INC-05 — s-Block Elements

Alkali Metal Properties and Trends

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Alkali Metal Data Table

Element	Z	Config	$IE_{1}$ (kJ/mol)	Atomic Radius (pm)	Flame Color	Reactivity with $H_{2}O$
Li	3	[He]2 $s^{1}$	520	152	Crimson red	Slow, steady
Na	11	[Ne]3 $s^{1}$	496	186	Golden yellow	Vigorous
K	19	[Ar]4 $s^{1}$	419	227	Violet	Very vigorous, catches fire
Rb	37	[Kr]5 $s^{1}$	403	248	Red-violet	Highly vigorous
Cs	55	[Xe]6 $s^{1}$	376	265	Blue	Explosive

Trends Down Group 1

Property	Trend	Reason
Atomic radius	↑ increases	New electron shell added each period
Ionic radius ( $M^{+}$ )	↑ increases	Follows atomic radius trend
Ionization enthalpy ( $IE_{1}$ )	↓ decreases	Increased radius, more shielding
Melting/boiling point	↓ decreases (general)	Weaker metallic bonds (larger radius)
Density	↑ increases (generally)	Mass increases faster than volume
Reactivity with $H_{2}O$	↑ increases	Lower IE, easier electron loss
Hydration enthalpy	↓ decreases	Larger ion, lower charge density

Key anomaly: Despite Li having the highest $IE_{1}$ , it is the strongest reducing agent in aqueous solution (E° = -3.04 V) due to its very high hydration enthalpy (-519 kJ/mol).

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