Question

What is the significance of the terms ‘isolated gaseous atom’ and ‘ground state’ while defining the ionization enthalpy and electron gain enthalpy?

Answer 1

As we know that ionisation enthalpy is the minimum amount of energy that should be supplied to remove an electron from an isolated gaseous atom to form a gaseous cation and the electron gain enthalpy is the amount of energy released when an electron is added to an isolated gaseous atom to form gaseous anion.

Complete answer:
As we know that ionisation enthalpy is the minimum amount of energy that should be supplied to remove an electron from an isolated gaseous atom to form a gaseous cation and the isolated gaseous atom is referred to as that the atoms in the gaseous states are so much separated that they do not have any mutual attraction or repulsion kind of interaction with other atoms which is basically called the isolated state of that atom.

And we also know that the electron gain enthalpy or electron affinity is the amount of energy released when an electron is added to an isolated gaseous atom to form gaseous anion and similarly it also consists of an isolated gaseous atom. Here the value of ionisation enthalpy and electron gain enthalpy are not at all influenced by the presence of other atoms.

Then we have ground state of an atom which is that state or level where the electron is present in its lowest energy state which is most stable state for an atom and thus the atom do not lose or gain any electron and both the ionisation enthalpy and electron gain enthalpy are expressed with respect to ground state of an atom only as when the atom is present in its excited state less amount of energy will be released when it gets converted to the gaseous anion after accepting an electron.

Note: Electron affinity is an exothermic process and moving down the group it decreases due to increase in size of an atom and along the period it increases whereas an ionisation energy process is endothermic and its low value indicates the greater electropositive, metallic and basic character of an element.