All compounds of alkali metals are easily soluble in water but lithium compounds are more soluble in organic solvents because the alkali metal compounds form ionic compounds due to their large ionic size and low ionization enthalpy, while lithium forms compounds of covalent nature due to their small ionic size, high ionization enthalpy, and high electronegativity. Ionic compounds dissolve in water, and covalent compounds dissolve in organic solvents.