Ionic Radius, Ionic Radius Periodic Table, Trends in Ionic Radius Across a Period (For CBSE, ICSE, IAS, NET, NRA 2022)

Doorsteptutor material for competitive exams is prepared by world's top subject experts: get questions, notes, tests, video lectures and more- for all subjects of your exam.

Ionic Radius

  • Ionic radius is the distance from the nucleus of an ion up to which it has an influence on its electron cloud.
  • Ions are formed when an atom loses or gains electrons. When an atom loses an electron, it forms a cation and when it gains an electron it becomes an anion. The Ionic radius can be described as the distance between the nucleus of an ion and the outermost shell of the ion.
  • The atomic size of a cation will be smaller than that of the parent atom. An anion is relatively larger in size than its parent atom. This is because when an atom gains electron the total number of electrons increases which tends to create more repulsion between electrons and thus overshadows the net effective nuclear charge.

Ionic Radius Periodic Table

Ionic Radius Periodic Table

For example,

  • Radius of potassium = 243 pm.
  • Radius of potassium ion = 138 pm.
  • Atoms and ions which consist of an equal number of electrons are considered as isoelectronic species. For example, both , have 10 electrons but they don՚t have the same ionic radius as the effective nuclear charge in both of them is different.
  • The radius of a cation will be smaller than that of the anion as a cation will have a greater positive charge (i.e.. , number of protons) so it will attract the electrons in the outermost orbital with greater force and hence the smaller size.

Trends in Ionic Radius Across a Period

In period 3 the atomic radius first decreases and then suddenly increases and then again it slowly decreases. This is because the starting elements in a period tend to form cations, and the elements towards the end of a period tend to form anions.

Trends in Ionic Radius Across a Period

Period 3

Number of protons111213151617
Electronic configuration2,82,82,82,8, 82,8, 82,8, 8
Ionic radius0.1020.0720.0540.2120.1840.181

Trends in Ionic Radius in Groups

In a periodic table while moving down in a group, atoms add extra shell (number of electrons) due to which ionic radius of elements increases down a group.

Trends in Ionic Radius in Groups
IonsConfigurationIonic radii (nm)IonsConfigurationIonic radii (nm)
2,80.1022,8, 80.181
2,8, 80.1382,8, 110.196


What is an Ionic Radius?


The ionic radius is the distance between the nucleus and the electron in the outermost shell of an ion.

How Do You Find Ionic Radius?


  • The ionic radius is half the distance between atomic ions in a crystal lattice. To find the value, ions are treated as if they were hard spheres.
  • The size of an element՚s ionic radius follows a predictable trend on the periodic table. As you move down a column or group, the ionic radius increase.

What Ionic Radius Depends On?


  • The ionic radius may be larger or smaller than the atomic radius (radius of a neutral atom of an element) , depending on the electric charge of the ion.
  • Cations are typically smaller than neutral atoms because an electron is removed and the remaining electrons are more tightly drawn in toward the nucleus.

Do Ions Have a Larger Atomic Radius?


  • Cations have smaller ionic radii than their neutral atoms. In contrast, anions have bigger ionic radii than their corresponding neutral atoms.
  • It will also decrease because there are now less electrons in the outer shell, which will decrease the radius size.

Developed by: