s-Block Elements: Essential NEET Facts

Group 1 = alkali metals ( $ns^{1}$ ); Group 2 = alkaline earth metals ( $ns^{2}$ )
Atomic radius is largest in each period for s-block elements; increases down a group
Ionization enthalpy is lowest in each period for Group 1; decreases down each group
All Group 1 metals show +1 oxidation state; Group 2 metals show +2 oxidation state
Flame colors: Li = crimson red, Na = golden yellow, K = violet, Rb = red-violet, Cs = blue
Oxide types (excess $O_{2}$ ): Li → $Li_{2}O$ (oxide), Na → $Na_{2}$$O_{2}$ (peroxide), K/Rb/Cs → K $O_{2}$ /Rb $O_{2}$ /Cs $O_{2}$ (superoxides)
Larger cations stabilize larger anions due to lattice energy considerations
Alkali metals dissolve in liquid $NH_{3}$ → solvated electrons (blue/bronze color) → strong reducing agent
Li-Mg diagonal relationship: both form normal oxides, carbonates decompose on heating, nitrates give oxide + N $O_{2}$ + $O_{2}$ , no solid bicarbonate, LiCl is covalent
Be-Al diagonal relationship: both have amphoteric oxides, covalent chlorides, max covalency 4, dissolve in NaOH
Solvay process: NaCl + $NH_{3}$ + C $O_{2}$ + $H_{2}O$ → $NaHCO_{3}$ ↓ (precipitates due to lower solubility) → $Na_{2}$$CO_{3}$ on heating
Castner-Kellner cell: mercury cathode electrolysis of brine → NaOH at cathode; $Cl_{2}$ at anode
Chlor-alkali process: modern electrolysis of brine → NaOH + $Cl_{2}$ + $H_{2}$
Be $Cl_{2}$ is linear in gaseous state; polymeric (chain) in solid state with bridging Cl
CaO (quicklime): formed at 1073 K from Ca $CO_{3}$ ; reacts exothermically with $H_{2}O$
Plaster of Paris sets by hydration: $CaSO_{4}$ ·½ $H_{2}O$ → $CaSO_{4}$ ·2 $H_{2}O$ (exothermic, slight expansion)
Portland cement = $Ca_{2}SiO_{4}$ + $Ca_{3}SiO_{5}$ + $Ca_{3}Al_{2}O_{6}$ ; gypsum (2-3%) slows setting
$Ca^{2+}$ forms hydroxyapatite in bones/teeth; critical for blood clotting and muscle contraction
$Mg^{2+}$ is the central metal atom of chlorophyll; enzyme cofactor for many reactions
$Na^{+}$ / $K^{+}$ control nerve impulse transmission via $Na^{+}$ - $K^{+}$ ATPase pump