Be differs from other Group 2 metals due to: (1) Exceptionally small size (smallest in Group 2) and very high charge density (+2 in tiny ion). (2) BeCl2 is covalent, polymeric in solid (linear chain with sp3 Be and bridging Cl), monomeric BeCl2 is linear (sp). Soluble in organic solvents. (3) BeO and Be(OH)2 are amphoteric: Be(OH)2 + 2HCl → BeCl2 + 2H2O; Be(OH)2 + 2NaOH → Na2[Be(OH)4]. (4) No d-orbitals — max covalence = 4 (forms [BeF4]^2- but not [BeF6]^4-). (5) Does not form peroxide (BeO only). (6) High IE $\frac{900 kJ}{mol}$ — does not react with water. (7) Diagonal relationship with Al: both form amphoteric oxides, covalent chlorides with bridging structures, carbides that give CH4 with water (Be2C + 4H2O → 2Be(OH)2 + CH4; Al4C3 + 12H2O → 4Al(OH)3 + 3CH4).