Question

when we talk abt metals we generally say that metals are hard bt the metals of s block especially 1st group can be easily cut with a knife why is it so why these metals are not hard??

Answer 1

Hardness depends upon cohesive energy that is the force holding the atoms or ions together in a solid. Cohesive energy, in turn depends upon the number of electrons that can participate in bond formation. The s-block elements have only one electron in their valence shell which can participate in bonding. So, they have low cohesive energy and consequently weak bonding. Thus, the alkali metals are soft.