How Large Is An Atom?

M. N. Murty

Visiting Faculty, Department of Physics, Sri Sathya Sai Institute of Higher Learning, Prasanthi Nilayam-515134, Andhra Pradesh, India.

The atomic radius of a chemical element is a measure of the size of its atoms. Atomic radii represent the sizes of isolated and electrically neutral atoms. In this paper, simple calculations for radii of hydrogen, helium and neon are given. Victor Weisskopf has calculated the radii of different atoms. To calculate the potential energy of electrons due to mutual repulsion among them, Weisskopf has assumed that the effective distance reff between two electrons is r/0.6, where r is the radius of the orbit of electrons. There is a good agreement between the calculated values and the experimentally measured values of the radii of atoms. The atomic radii gradually decrease along each period of the periodic table, from the alkali metals to the noble gases; and increase down each group. The radii of isolated neutral atoms range between 0.3 and 3 angstroms. The radius of an atom is a function of its environment.