Electron Configurations for a Group What is the

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 spin. The three rules are applied simultaneously to get the electronic configuration. In writing the electronic configuration, an orbital is shown by using its proper symbol.The number of electrons present in an orbital is shown as the right-hand superscript of the symbol of the orbital. 1 For example, the electronic configuration of hydrogen is 1s . This means that the single electron in hydrogen occupies the s orbital present in the principal energy level n = 1. Similarly the electronic configuration of other elements are written. Furthermore, for simplicity a common convention is used. In this, the detailed electronic configuration of the noble gas core preceding the valence shell is represented by the symbol of the noble gas in square brackets. Then, the configuration of the valence shell is written after the symbol. For example, the electronic configuration of sodium may be written as Na(Z = 11) : [Ne]3s Step2: n np 6is a fulfilled configuration, i.e., all the orbitals are completely occupied. Out of all the elements in the periodic table, only the noble gases have all fully occupied orbitals as shown below: Thus, the correct option is (d). -----------------