Li is different from other alkali metals in many aspects and resembles a diagonal relation to Mg due to their similarities in the following properties:
1. Li+ and Mg++ have similar ionic sizes and high polarizing power.
2. Li and Mg both react slowly with H2O but other alkali metals react vigorously with water.
3. Both are harder and have a high melting point in comparison to other metals in their respective group.
4. Li forms Li2O and Mg also gives MgO While other gives peroxide and superoxide.