# How to find Atomic Radius? – [ Define, Chart ]

At the end of the article, you will able to describe How to find Atomic Radius, Chart with values, Various methods and why it is difficult to measure exact Atomic Radius.

If someone you what do you think would be atomic radius? The obvious answer would be – it’s the radius of an atom. What if I ask you define it then the proper definition for atomic radius would be

It is the distance from the center of the nucleus to the outermost shell.

Just taking the distance and that is the atomic radius is not so simple. why? Because you are dealing with a very very small particle which has a size of 10-10 m.

### Why difficult to find exact atomic Radius?

For such a small atom,

• It would be very difficult for us to find the atomic radius accurately.

The second reason because of which finding out the atomic radius becomes very difficult is

• The probability density picture.

If you recall the probability density picture, you see that the probability of finding an electron in an atom at a very large distance from the nucleus cannot be zero ( except some places).

Similar to that, If we take the crowd the picture of the electron in the surrounding or if there are neighboring atoms then those neighboring atoms would also cause some sort of a distortion to the electron cloud.

• This would also result in the inaccuracies of atomic radius

Last reason because of which atomic radius will not be found out accurately is

• The size of the atom changes with the change in its bonding state.

So, if it is covalently bonded it might have a different radius. If it is metallic bonding it might have something else. Take up all, these will consider these all factors and what you are left with is called as the effective atomic radii. So, where ever we are going to study its the actual effective atomic radii and not the atomic radius wishes from the center to the outermost shell.

## How to find Atomic Radius?

• The distance can be measured by the X-ray diffraction and spectroscopic method. Thus
• Stevenson’s formulaIn Heteroatomic atoms, covalent radius shifted towards the higher electronegative element. Then, the covalent radius is calculated by the relation which is called Stevenson’s formula as follows:

dAB = rA + rB – C|xA – xB|

Where rA and rB = radius of an atom ‘A’ and atom ‘B’

dAB =  predicted bond length(distance between two atoms)

|xA – xB| = difference in the electronegativities of elements A and B.

C is a constant.

 Period  Group IA IIA IIIA IVA VA VIA VIIA Zero 1. H 0.37 He 0.93 2. Li 1.34 Be 0.90 B 0.82 C 0.77 N 0.73 O 0.74 F 0.72 Ne 1.31 3. Na 1.54 Mg 1.30 Al 1.18 Si 1.11 P 1.06 S 1.02 Cl 0.99 Ar 1.74