An atom is assumed to tbe spherical in shape and thus, the size of atom is generally given in terms
Channel: Doubtnut
Date: 12/04/2020

An atom is assumed to tbe spherical in shape and thus, the size of atom is generally given in terms of radius of the sphere and is called atomic radius. It is usually defined as the distance between the centre of the nucleus and outermost shell where electron are present. The exact measure of atomic radius is not easy due to following reasons:   (i) The atom does not have well defined boundary. the probability of finding the electron is never zero even at large distance from the nucleus.  (ii) It is not possible to get an isolated atom. the electron density around an atom is affected by the presence of neighbouring atoms, i.e., the size of the atom changes in going from one set of environement to another.   (iii) the size of an atom is very small, of the order of about 1.2  Å,i.e., `1.2xx10^(-10)m`.   An estimate of the size of the atom can, however, be made by knowing the distance betweent he atoms in the combined state. the distance between the atoms, i.e., bond length are generally measured by the application of techniques such as X-ray differaction, electron diffraction, infrared spectroscopy, nuclear magnetic resonance spectroscopy, etc. However, bond lengths change with different type of bonding. Three types of radius are commonly used, i.e.,   (a) Covalent radius `"     "` (b) crystals radius `"     " ` (c) Vander waal's radius  The correct order of effective nuclear charge `Z_(eff)` is