Chapter : 7. Periodic Classification of Element
Periodicity in Properties, Atomic Size (Atomic radii), Covalent Radii and Radius
Periodicity in Properties :
The properties of elements depends upon the electronic configuration which changes along a period and down a group in periodic table.
There is periodicity in properties, i.e., repetition of properties after a regular interval due to similarity in electronic configuration.
Atomic Size (Atomic radii) :
Atomic size means radius of an atom. It is defined as distance between centre of nucleus and outermost shell (valence shell) of an isolated atoms.
Covalent Radii :
It is defined as half of the distance between the centres of nuclei of two atoms (bond length) bonded by a single covalent bond, e.g., Bond length in case of H—H (Hydrogen molecule) is 74 pm.
Covalent radius = 1/2 × 74 pm = 37 pm (picometre) [1 pm = 10–12 m]
It can be measured in case of diatomic molecules of non-metals.
Metallic Radii : If is defined as half of the internuclear distance between the two metal ions in a metallic crystal. It is measured in case of metals.
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