Assuming atom to be spherical, the distance between the nucleus and the outermost orbit of the atom is called the atomic radius of the element. However, it can not be determined precisely due to the following reasons:
(i) Atom is too small to be isolated.
(ii) According to the probability picture of electrons, an atom does not have a well-defined boundary.
(iii) The probability distribution of an atom is also affected by the presence of other atoms in its neighbourhood.
(iv)The size of the atom also changes from one bonding state to another.
Thus, it is not possible to determine the absolute value of atomic radius practically. In other words, atomic radius has no meaning.
Why do the noble gas elements have exceptionally high atomic radii?
Or
In a period, generally the size of the atom decreases with rise in atomic number, but at the end of each period, atomic size of the noble gas increases abruptly. Why is it so?
