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SUBJECT-CHEMISTRY

CHAPTER- Periodic classification of elements

SUBTOPIC- Atomic radius

KEY NOTES :

Periodic properties :

(1)Atomic radius :

The distance from the centre of the nucleus to the outermost shell
containing electrons is called atomic radius.

 The size of the atom can not be determined accurately since :

 The electron cloud surrounding the atom does not have a sharp
boundary.

 It is not possible to isolate a single atom.

 The probability distribution of electrons of an atom is affected by the

presence of other atoms within its molecule. So atomic radius may
change in going from one environment to other.

 The atomic radius also changes when the atom is present in different
bonded states.

Due to these four reasons the exact value of atomic radius of an atom can

not be determined accurately.

 The atomic radius can be calculated by using following terms :

 Covalent radius

 van der Waal's radius

 Metallic radius

 (i)Covalent radius :

 It is defined as one-half the distance between the nuclei of two
covalently bonded atoms of the same element in a molecule.