Ionic Radius

Understanding formation of Ionic radius(RIonic): An atom has three fundamental subatomic particles electron, protons, and neutrons. Proton is having a positive, electron is having a negative charge and neutron have no charge.The number of electrons present in the outermost shell decides the chemical and the physical properties of an element.The radius of atom changes when it loses or gains an electron. If the ion is formed by loss of one or more electron we call as a cation( positive ion). If an atom gains an electron from another atom we called as an anion (negatively ion).

Ionic Radius

What is Ionic Radius?

It is the effective distance from the center of the nucleus of the ion up to which it exerts its influence on the electron cloud.- OR-. The radius of cation or anion.

.When an atom gains one or more electrons, atom changes to an anion. Since the nuclear charge remains unchanged, the number of electrons in an anion experience less attraction towards the proton compared with the atom. Therefore, RIonic  is larger than that of the corresponding atom.

In the formation of cations, there is a loss of electron(s) and the number of protons remains. So, overall the protons are more in counting than number electrons present. Hence there is a decrease in the radius.

Ionic Radius Definition

The distance from the center of nucleus up to which (proton) nuclear charge exerts influence on electrons.

It should be noted that:

  • The size of the ion increases with the increase of negatively charged.
  • The size of cation decreases with the increase of positively charged.

Must Read: Atomic Radius

How to Find Ionic Radius?

Some theoretical methods have been given so as to calculate the radius of an ion. The most suitable values are as given by Pauling scale are most acceptable.

It is quite easy to determine the internuclear distance between the two oppositely charged ions (say Na+ and Cl) in the crystal lattice by X-ray studies. If the absolute radius of one of them is known, then other can be easily obtained by subtracting the same from inter nuclear distance. For example: in sodium chloride crystals, the inter-nuclear distance is 276 pm and the radius of Na+ ion is 95 pm,(Pauling method).Therefore the radius of Clion is 276 – 95=181 pm.

Ionic Radius Chart Table

Atom  Li Na K Rb Cs
Atomic radius (Å)

1.34

1.54

1.96

2.11

2.25

RIonic (Å) [M]

0.60

0.95

1.33

1.48

1.69

Atom  F Cl Br I
Atomic radius (Å)

0.72

0.99

1.14

1.33

RIonic (Å) [M]

1.36

1.81

1.95

2.16

Ionic Radius Trend

It may be noted that the value of ionic radius linked with the atomic radius and varies accordingly. Thus, the RIonic always increases down the group and decreases along the period provided the ions involved have the same magnitude of charge.

If there is a change in nuclear charge then:

  1.  In a group, the ionic radius increases from top to bottom. It shows no regular pattern in periods.
  2. Ionic radii are inversely proportional to nuclear charge. Ionic radii in the nth orbit is given as:

  • Where  n = principle quantum number
  • Z = effective nuclear charge.

 

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