What is First Ionization Energy – Definition, Trend, Chart

At the end of the article, you will able to describe – What is First Ionization Energy, Definition, Trend, Chart. Let’s start discussing one by one.

What is First Ionization Energy – Definition

A measurement that how strongly an atom holds its electrons is called Ionization energy. The removal of a single electron is known as the First Ionization energy.

Atom + Ionization Energy → Positive ion + Electron

With the removal of an electron from a neutral atom, the remaining electrons experience greater attraction towards the nucleus. Hence, considerably more energy is required to remove the second electron.

Units = The amount of energy taken by all of the atoms in a mole of a substance. This energy helps to lose electrons. Expressed as –

  • kilojoules per mole (kJ/mol) or
  • kilocalories per mole (kcal/mol).

Let’s talk about first I.E and successive Ionization energies.

First Ionization Energy 

It is easy to remove the loosely bonded electron from the outermost orbit. Both first Ionization potential and first I.E have the same meaning.

First Ionization:              Na (g) + E1→Na+ (g) + e

It is due to fact that attraction between proton and electron will increase the ionization enthalpy. Increases in the binding force results increase of ionization enthalpy. First I.E (enthalpy) of elements are linked with their electronic configurations.

Lowest Ionization Energy – The ejection of electrons from caesium metal is easy because caesium element has the tendency to hold the electrons loosely because ionization enthalpy is very low.

Second Ionization Energy

Similarly, the energy required for the removal of an electron from the unipositive ion (produced above) is referred to as second ionization potential.

Second Ionization:              Na+ (g) + E2→Na2+ (g) + e

and thus the third, fourth, etc. ionization potentials may be defined. In general, the number of ionization potentials of an element may be as much as its number of electrons.

First Ionization Energy Trend

The Trend in the first Ionization Energy has many exceptions.

  • Generally, In each period, I.E maximum at noble gases while minimum energy notice at the alkali metals. When an electron removes from the outermost orbit, then the first I.E is found to be maximum in alkali metals. It will achieve 2s22p6configuration.
  • The second ionization energy, IE2 is always more than the first IE1. It is because in the 2nd ionization energy or potential, an electron is to be removed from a positive ion which has the attraction for electrons and thus makes removal of an electron a difficult task.
  • Thus in general Third IE >>> Second IE > First IE.

Successive Ionization Energies

Element IE1 IE2 IE3 IE4
Li 520.1 7297 11813 ––
C 1086.2 2352 4620 6221
N 1402.1 2856 4577 7474 

The I.E trend changes when moving across period and group. The minimum energy required to remove electron varies and depends upon the number of factors.

Question: Be has higher ionization potential than B – Explain?

  • Be has fully filled orbital (1s22s2)
  • Boron does not have a fully filled orbital (1s22s22p1).

Again s electron is more penetrating than p-electron. So, more energy required to remove an electron from 2s orbital than to 2p orbital. So Be has higher I.E.

First Ionization Energy Chart

What is First Ionization Energy - Definition, Trend, Chart


This is all about the basics – What is First Ionization Energy, Definition, Trend, Chart.

Translate it with Google »