Ionization Potential or Enthalpy of An Atom


An atom consists of a nucleus and electrons revolve around this nucleus in a circular orbit. The nucleus contains neutrons and positively charged particles, protons and hence the electrons are attracted to the nucleus. Energy has to be provided to overcome this force of attraction to remove the electron from an atom or molecule. After the electron has been eliminated from the atom, the atom acquires a unit positive charge and becomes a positively charged ion (cation). The energy required to remove an electron from a neutral gaseous atom so as to convert it into a positively charged ion is called Ionization Potential or first ionization potential or energy.

M (g) + I.E. → M+ (g) + e ,

Where M can be any element and I.E. is the ionization potential or energy. The I.E. is measured in electron volts per atom, and its SI unit is kilojoule per mole.

Ionization energy that is required to remove the second electron from a monovalent cation is known as second ionization potential. Similarly, the energy needed to remove the third electron from a divalent cation is known as third ionization energy and so on. The value of ionization energy increases as the charge on the cation increases. Therefore, the successive ionization energies have higher costs.

Ionization potential depends on two factors:

  1. Atomic size: The greater the atomic size, lesser will be the force of attraction by the nucleus. As the electrons in the outermost shell will lie far away from the nucleus, their removal will be easy that means the value of ionization potential will be less. So with the increase in atomic radius, ionization potential decreases.
  2. Nuclear charge: The greater the nuclear charge more will be the force of attraction on the electrons. This means that the nucleus will firmly hold the electrons and more energy will be required to remove it from the atom.

Ionization energy tends to increase across a period in the modern periodic table as the atomic size decreases and the nuclear charge increases on moving from left to right. But it decreases down a group with an increase in atomic size.

The article briefly describes the key points of ionization energy. For any further query on this topic, install Byju’s the learning app.


Practise This Question

Considering entropy (S) as a thermodynamic parameter, the criterion for the spontaneity of any process is