What is anomalous nature of lithium?

Lithium behaves differently as compared to other alkali metals. This is mainly because of the following reasons:
1. The extremely small size of lithium atom and its ion.
2. Greater polarizing power of lithium ion ( Li+), due to its small size which result in the covalent character in its compounds.
3. Least electropositive character and highest ionization energy as compared to other alkali metals.
4. Non availability of vacant d-orbitals in the valence shell.