# Bohrâ€™s Model

In any atom, electrons can rotate only in a certain selected (or permissible) orbits without radiating energy. Such orbits are known as stable or non-radiating orbits or stationary states. These orbits are circular with well-defined radii. These radii are numbered 1, 2, 3,â€¦ (from the nucleus). Orbits are paths of revolution of electrons. A spherical surface around the nucleus, which contains orbits of equal energy and radius, is called a shell. The shell are denoted as K, L, M, N, â€¦.

Each stationary state (or orbit) corresponds to a certain energy level (i.e., as long as the electron is in the particular stationary state, it has a definite amount of energy). The energy associated with an electron is least in the K shell and it increases as we pass to L,M, N, â€¦ shells.

An electron can jump from one stationary state to another. For an electron to jump from an inner orbit of energy E1 to an outer orbit of energy E2, it should absorb the equivalent of a quantum of energy = E2 â€“ E1 = hÎ½, where Î½ is the frequency of radiation absorbed. Similarly, when it jumps back from the outer to the inner orbit, it will emit an equal amount of energy in the form of radiation.

According to Bohr, angular momentum is given by
âˆ´

where n is a positive integer 1, 2, 3, â€¦ and is known as a quantum number. Therefore,

Solving for r, we get

= â€“2.179 Ã— 10â€“18 J per atom = â€“13.6 eV per atom

E = â€“1312 kJ/mol