Anomalous Behavior of Beryllium

Beryllium shows anomalous behavior compared to other Group 2 metals due to:

Property	Beryllium (Anomalous)	Other Group 2 (Normal)
Oxide character	BeO is amphoteric (dissolves in HCl AND NaOH)	MgO, CaO are basic only
Chloride bonding	$BeCl_{2}$ is covalent (polymeric solid, melts at 405°C)	$MgCl_{2}$ , $CaCl_{2}$ are ionic
Max covalency	4 (only s and p orbitals available)	Higher (d-orbitals accessible for Mg and beyond)
With NaOH	Be dissolves: Be + 2NaOH + $2H_{2}O$ → $Na_{2}$ [Be(OH)_{4}] + $H_{2}$	Mg, Ca, etc. do NOT dissolve in NaOH
Diagonal relationship	Be ~ Al (similar charge density)	No equivalent relationship

Solid state: Polymeric chain (each Be is $sp^{3}$ hybridized, tetrahedral coordination with 4 Cl atoms — 2 bridging, 2 terminal)

Vapour phase (high temp): Linear monomer (Be is sp hybridized, bond angle 180°, electron-deficient)

$Beryllium chloride (BeCl_{2}) structure$

Reactions of BeO: $BeO + 2HCl \rightarrow BeCl_2 + H_2O\ \ (acts\ as\ base)$ $BeO + 2NaOH \rightarrow Na_2BeO_2 + H_2O\ \ (acts\ as\ acid)$