The enthalpy change when an e is attached to an atom is called electron gain enthaly. A negative value indicates formation of stable anion. Electron affinity is the qualification ascribed to the above term. An element with more electron affinity will have a higher negative value of electron gain enthalpy. Bohr,s postulates given in 1913 assumes i) electrons move in circular orbits about the nucleus, ii) an orbit can have upto 2n squared no. of e (n = s. No. 1 , 2, 3, infinity of orbits), and iii)nuclear pull on e (inward) is balanced by outward cetrifulal force. His most important postulate was that only those orbits are allowed in which the angular momentum of e (m x v x r) was an exact multiple of h/2pi.