Atomic radius

Atomic radius of an element may be defined as the distance from the centre of the nucleus of the atom to its outer most shell 
Atomic radius of an element is not possible to measure in its isolated state.this is because it is not possible to determine the location of the electron that surrounds the nucleus.however,we can measure the distance between the nuclei of adjacent atoms in a solid.from this we can estimate the size of the atom by assigning half of this distance to the radius of each atom.this method is best suited to elements such as the metals that exist in the solid state.more than 75 percent of the elements are metals and atomic radii of metals are called metallic radii.
Another way of estimating the size of an atom is to measure the distance between the two atoms in covalent molecules.
The size of a chlorine atom is estimated by measuring the length of the covalent bond between two chlorine atoms in a cl2 molecule.
Half of this distance is taken as atomic radius which is called as the covalent radius of the chlorine atom.
Atomic radius is measured in 'pm' (pico meter) units.
1pm =10-12m

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