Sodium and potassium crystallise in body centred cubic structure. In this ,unit cell consists of eight atoms at eight corners of cube and one atom at the centre of the cube. There is lot of empty space in the unit cell ,hence metallic bond is weaker. Thus sodium and potassium metals appear soft and can be cut with knife. read more
i) Alkali metals are placed at the extreme left of the periodic table. They belongs to group number I or IA. Alkali metals have large atomic size with only one valence electron. Terefore, they have weak metallic bonding between the atoms. Due to the presence of weak metallic bonding alkali metals are soft and can be cut with a knife. read more
All metals cannot be cut with knife. Only sodium, potassium and calcium can be cut with knife because they are soft in nature. read more