Question

Question 3.14 What is the significance of the terms - ‘isolated gaseous atom’ and ‘ground state’ while defining the ionization enthalpy and electron gain enthalpy?

Hint: Requirements for comparison purposes.

Class XI Classification of Elements and Periodicity in Properties Page 93

Answer 1

first of all we have to know what is ionisation energy?
ionisation energy is the amount of energy required to remove an electron from an isolated gaseous atom (X ) in ground state.
e.g., X (g) -------> X⁺(g) + e- .
Here you see that ionisation energy or enthalpy is determined of isolated gaseous atom in ground state . because in isolated gaseous state interatomic distance are larger and interatomic force are minimum. due to this reasons , isolated gaseous atom in ground state has been included in defined ionisation energy or enthalpy.

Electron gain enthalpy :- it is the amount of energy released when an isolated gaseous atom (X) in ground state gains an electron to form gaseous anion.
e.g., X(g) + e- ------> X⁻ (g)
we know, the most stable state of an atom is ground state . if isolated gaseous atom is in excited state comparatively lesser energy will be released of an electron . so, electron gain enthalpies of gaseous atom must be determined in their ground state .

Answer 2

Answer:

Ionization enthalpy is the energy required to remove an electron from an isolated gaseous atom in its ground state. Although the atoms are widely separated in the gaseous state, there are some amounts of attractive forces among the atoms. To determine the ionization enthalpy, it is impossible to isolate a single atom. But, the force of attraction can be further reduced by lowering the pressure. For this reason, the term ‘isolated gaseous atom’ is used in the definition of ionization enthalpy.

Ground state of an atom refers to the most stable state of an atom. If an isolated gaseous atom is in its ground state, then less amount energy would be required to remove an electron from it. Therefore, for comparison purposes, ionization enthalpy and electron gain enthalpy must be determined for an ‘isolated gaseous atom’ and its ‘ground state’.