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First elements of Groups 1 and 2 show anomalous properties due to their very small size and high charge density.

Lithium anomalies: (1) LiF, Li2CO3, Li3PO4 are insoluble. (2) LiCl is covalent, soluble in organic solvents (Fajans' rules). (3) Forms only Li2O $\frac{no peroxide}{superoxide}$. (4) Li2CO3 decomposes on heating. (5) Forms Li3N directly with N2. (6) LiOH is weak base. (7) Hardest alkali metal.

Beryllium anomalies: (1) BeO and Be(OH)2 are amphoteric. (2) BeCl2 is covalent, polymeric (sp3 bridging). (3) Max covalence = 4 (no d-orbitals). (4) Doesn't react with water. (5) No peroxide formation. (6) Very high IE $\frac{900 kJ}{mol}$.

Li-Mg diagonal relationship: Similar charge/radius ratio. Both form nitrides directly (Li3N, Mg3N2). Both carbonates decompose. Both halides are covalent. Both fluorides and phosphates are insoluble. Neither forms solid bicarbonates.

Be-Al diagonal relationship: Both form amphoteric oxides/hydroxides. Both form covalent, bridged chlorides (BeCl2 polymer, Al2Cl6 dimer). Both carbides are methanides (give CH4 with water: Be2C, Al4C3). Both dissolve in excess NaOH forming [M(OH)4]^n-. The underlying cause is comparable charge density and electronegativity values for diagonally placed elements.