What is ionisation enthalpy ? Why caesium has less value of ionisation enthalpy ?
What is ionisation enthalpy ? Why caesium has less value of ionisation enthalpy ?
Ionisation Enthalpy is defined as the minimum amount of energy required to liberate an electron which is loosely bound to the outermost shell, from an isolated gaseous atom in its ground state to convert it into a gaseous cation.
A (g) ―> A+ (g) + e-
Cesium is the second last member of Ist Group (Alkali Metals) and has the lowest value of Ionisation Enthalpy because of its largest size among alkali metals. This is because atomic size increases on moving down the group due to addition of one new principal energy shell at each element consequently, the number of inner electrons increases which shields the valence electron from nucleus. Hence, in Cesium the valence electron is held very loosely as compared to other alkali metals. The order of variation of Ionisation Enthalpy among alkali metals is : Li> Na> K> Rb> Cs.
Ionisation Enthalpy is defined as the minimum amount of energy required to liberate an electron which is loosely bound to the outermost shell, from an isolated gaseous atom in its ground state to convert it into a gaseous cation.
A (g) ―> A+ (g) + e-
Cesium is the second last member of Ist Group (Alkali Metals) and has the lowest value of Ionisation Enthalpy because of its largest size among alkali metals. This is because atomic size increases on moving down the group due to addition of one new principal energy shell at each element consequently, the number of inner electrons increases which shields the valence electron from nucleus. Hence, in Cesium the valence electron is held very loosely as compared to other alkali metals. The order of variation of Ionisation Enthalpy among alkali metals is : Li> Na> K> Rb> Cs.
