Ionization Energy, Application, Comparison, Important Facts, JEE Chemistry 2024

Ionization Energy : Ionization Energy, also referred to as Ionisation Enthalpy or Ionisation Potential, is a fundamental concept in the field of chemistry that elucidates the energy required to remove an electron from an atom or ion in its gaseous state.

This energy quantifies the strength of the attraction between the negatively charged electron and the positively charged nucleus within an atom, dictating various chemical properties and reactions. Moreover, Ionization Energy plays a significant role in predicting trends across the periodic table and explaining the formation of ions in various chemical processes.

Ionization Energy

Ionization Energy : Ionization energy, also known as ionization potential, is defined as the energy required to remove an electron from an atom or ion in its ground state. It is typically measured in units of kilojoules per mole (kJ/mol) or electron volts (eV). The process of removing an electron from an atom results in the formation of a positively charged ion.

The ionization energy of an atom depends on several factors, including the nuclear charge, electron-electron repulsions, and the distance of the electron from the nucleus. Generally, ionization energy increases across a period in the periodic table due to increasing nuclear charge and decreases down a group due to increasing atomic size.

(a) For an atom M _(g) successive ionization energies are as follows-

E ₁ = I ^st Ionization energy

E ₂ = II ^nd Ionization energy

E ₃ = III ^rd Ionization energy

E ₁ < E ₂ < E ₃ ………. (Always for an element)

(b) Electron can not be removed from solid state of an atom, it has to be convert into gaseous form, Energy required for conversion from solid state to gaseous state is called Sublimation energy.

(c) For any neutral atom ionization energy is always an endothermic process (ΔH = +ve)

(d) It is measured in eV/atom (electron volt/atom) or Kcal/mole or KJ/mole

Important Factors Affecting Ionization Energy

(i) Effective nuclear charge (Z _eff )

Ion with high positive oxidation state will have high ionization energy.

Ex. Fe ⁺³ > Fe ⁺² > Fe

(ii) Stability of half filled and fully filled orbitals:

Half filled p ³ , d ⁵ , f ⁷ or fully filled p ⁶ , d ¹⁰ , f ¹⁴ are more stable than others so it requires more energy.

IE ₁ N > O

1s ² , 2s ² 2p ³ 1s ² , 2s ² 2p ³

After loosing one e ^– , O attains electronic configuration of N, so II ^nd ionization energy of O is more than N.

IE ₂ N < O

1s ² , 2s ² 2p ² 1s ² , 2s ² p ³

(iii) Penetration power of sub shells:

(a) Order of attraction of subshells towards nucleus (Penetration power) is s > p > d > f

(b) ‘s’ subshell is more-closer to nucleus so more energy will be required to remove e ^– from s-subshell as comparison to p, d & f subshells.

Ex. Be B

1s ² , 2s ² 1s ² , 2s ² , 2p ¹

IE ₁ Be > B

After loosing one e ^– , B attains electronic configuration of Be, so II ^nd ionization energy of B is more than Be.

IE ₂ Be < B

1s ² , 2s ¹ 1s ² , 2s ²

In a group:

Comparison of Ionization Energy

(i) In a period: Z _eff increases so removal of electron becomes difficult and ionization energy increases.

Order of IE of 2 ^nd period elements Li < B < Be < C < O < N < F < Ne

(ii) In a group: Size increase so ionization energy decrease.

Size increases, Ionization Energy decreases

Exception

Exception:

• Ionization Energy Ga > Al (due to Transition contraction)

• Ionization Energy of 5d > 4d(due to lanthanide contraction)

Ex. Hf > Zr

Application of ionization energy

(A) Metallic and non-metallic character:

Generally, for metals Ionization Energy is low.

For non-metals Ionization Energy is high.

Metallic character ∝

(B) Reactivity of metals:

Reactivity of metals

Reactivity of metals increases down the group as ionization energy decreases.

(C) Stability of oxidation states of an element:

(a) If the difference between two successive ionization energy of an element ≥ 16eV, then its lower oxidation state is stable.

Ex.

Difference between ionization energy >16eV.So Na ⁺ is more stable.

(b) If the difference between two successive ionization energy of an element ≤ 11 eV, then its higher oxidation state is stable.

Ex.

Difference of ionization energy < 11eV.  So, Mg ⁺² is more stable.

Ex. is more stable

is more stable

Overall order of stability is Al ⁺³ > Al ⁺ > Al ⁺²

(D) To determine the number of valence electron of an element:

Number of valence electrons = Number of lower values of IP before 1 ^st highest jump.