Physical Properties of Alkali Metals

Alkali metals are placed in group 1 of periodic table. They readily form unipositive ions. As we go down the group, the alkali metals show steady increase in size due to the addition of a new shell at each step. The increase in size of the atoms or ions, directly influences the physical and chemical properties of the alkali metals.

Oxidation State

All elements show +1 oxidation state

Atomic or Ionic Radii

Li < Na < K < Rb < Cs

Atomic and ionic radii increases since number of shells increase as we go down the group.

Ionization Energy

Li > Na > K > Rb > Cs

As the size increases it becomes easier to remove an electron from the outermost shell.

Electronegativity

Li > Na > K > Rb > Cs

The electropositive character increases due to decrease in ionization enthalpy therefore electronegativity decreases.

Metallic Character

Li < Na < K < Rb < Cs

Metallic character increases as we go down the group due to increase in electropositive character.

Density

Li < Na > K < Rb < Cs

Generally density increases from Li to Cs as the atomic mass increases (exception K).

Melting Point & Boiling Point

Li > Na > K > Rb > Cs

Decreases down the group because of increasing size and weak inter-metallic bond.

Flame Coloration

They show characteristic colors in the flame. The outermost electron absorbs energy and is excited to a higher energy level. This absorbed energy is remitted when the electron comes back to ground state. The difference in energy falls in the visible range of radiation, hence the colors are seen.

• Li: Crimson red
• Na: Yellow
• K: Pale violet
• Rb: Violet
• Cs: Violet