Question

What are the common physical features of alkali metals?

Answer 1

Physical properties of alkali metals are as follows.

1. They are quite soft and can be cut easily. Sodium metal can be easily cut using a knife.
2. They are light coloured and are mostly silvery-white in appearance.
3. They have low density because of their large atomic sizes. The density increases down the group from Li to Cs. The only exception to this is K, which has a lower density than Na.
4. The metallic bonding present in alkali metals is quite weak. Therefore, they have low melting and boiling points.
5. Alkali metals and their salts impart a characteristic colour to flames. This is because the heat from the flame excites the electron present in the outermost orbital to a high energy level. When this excited electron reverts back to the ground state, it emits excess energy as radiation that falls in the visible region.
6. They also display a photoelectric effects. When metals such as Cs and K are irradiated with light, they lose electrons.