Question

Explain electron gain enthalpies of the noble gases are positive.

Answer 1

• Electron gain enthalpy of an element is the energy released when a neutral isolated gaseous atom accepts an extra electron to form the gaseous negative ion i.e. anion.
  
• The atoms of the noble gases have completely filled subshell. As a result, there is no room in their valence orbitals and the additional electron has to be placed in an orbital of next higher shell. As a result, energy has to be supplied to add on additional electrons. So electron gain enthalpies of noble gases are positive.