Orbital Diagrams and Electron Configurations Draw the orbital diagram for the electron configuration of oxygen, atomic number 8. How many unpaired electrons does an oxygen atom possess? (a) Write the electron configuration for silicon, element 14, in its ground state, (b) How many unpaired electrons does a ground-state silicon atom possess?
Solution: Here, we are going to write the electronic configuration of Silicon and determine the number of unpaired electrons in it. 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 and p xof ye p - szshell 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. Step2: The atomic number of silicon is 14. Based upon the rules given above, the electronic configuration of silicon can be written as: 1s 2s 2p 3s 3p 2 Step3: The orbital diagram for the above configuration is: From the orbital diagram above, it is seen that silicon has 2 unpaired electrons in its ground state. ---------------------------------