Oxide type in excess $O_{2}$: Li → $Li_{2}O$ (oxide), Na → Na_{2}$$O_{2} (peroxide), K/Rb/Cs → superoxides (K$O_{2}$). Larger cation = larger anion stabilized.

Solvay process trap: $NaHCO_{3}$ precipitates because it is least soluble — NOT because it forms first.

Li anomaly: Li resembles Mg (diagonal relationship): normal oxide only, carbonate decomposes, $LiNO_{3}$ gives $Li_{2}O$ + N$O_{2}$ + $O_{2}$, no solid $LiHCO_{3}$.

Be anomaly: Be resembles Al: both have amphoteric oxides, covalent chlorides, and max covalency of 4.

Plaster of Paris sets by hydration: $CaSO_{4}$·½$H_{2}O$ + 3/2$H_{2}O$ → $CaSO_{4}$·2$H_{2}O$ (gypsum); exothermic with slight expansion.