Electron Configurations for a Group What is the characteristic valence electron configuration of the group 7 A elements, the halogens? A certain atom has an ns2np6 electron configuration in its outermost occupied shell. Which of the following elements could it be? (a) Be (b) Si (c) I (d) Kr (e) Rb
Solution: Here, we are going to identify the element having outermost electronic 2 6 configuratio n s . Step1: The distribution of electrons in different orbitals is known as electronic configuration of the atom. The filling of orbitals are governed by the following rules: a) Aufbau principle: The Aufbau principle states that in the ground state(lowest energy state) of an atom, an electron enters the orbital of lowest energy first and subsequent electrons are fed in the order of increasing energies. The orbital should be filled in the following sequence: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, ………. b) Pauli’s exclusion principle: According to this principle an orbital can accommodate maximum of two electrons and these must have opposite spins. c) Hund’s rule of maximum multiplicity: According to this rule, electron pairing will not take place in orbitals of same energy(subshell) until each orbital is singly filled. For example, there are three p- orbitals(p , p andx yof thez - subshell in a principal energy level. According to Hund’s rule, each of the three p-orbitals must get one electron of parallel spin before any one of them receives the second electron of opposite...
