The alkali metals emit electrons when radiation strikes on their surfaces. This phenomenon of emission of electrons when electromagnetic radiation strikes against them is called the photoelectric effect. Therefore, alkali metals exhibit the photoelectric effect.
Alkali metals have low ionisation enthalpies and therefore, the electrons are easily ejected when exposed to light.
- Among alkali metals, caesium has lowest ionisation enthalpy and hence it can show photoelectric effect to the maximum extent.
- Alkali metals (except Li) exhibit the photoelectric effect. The ability to exhibit the photoelectric effect is due to the weak value of the ionization energy of alkali metals. Lithium does not emit photoelectrons due to the high value of ionization energy.