Chemistry > Structure of Atom > 14.0 Electronic Configuration of Elements
Structure of Atom
1.0 Introduction
2.0 Cathode Ray Discharge Tube
3.0 Thomson Model of Atom
4.0 Rutherford Model of Atom
5.0 Atomic Number and Mass Number and It's Relation
6.0 Planck's Quantum Theory
7.0 Bohr’s Atomic Model
8.0 Dual Behaviour of Matter
9.0 Heisenberg Uncertainity Principle
10.0 Photoelectric Effect
11.0 Atomic Spectra
12.0 Quantum Mechanical Model of Atom
13.0 Quantum Number
14.0 Electronic Configuration of Elements
14.1 Aufbau (or building up) Principle
14.2 Pauli’s Exclusion Principle
14.3 Hund’s Rule
14.4 Stability of Completely Filled and Half Filled Subshells
14.3 Hund’s Rule
14.2 Pauli’s Exclusion Principle
14.3 Hund’s Rule
14.4 Stability of Completely Filled and Half Filled Subshells
- This rule concerns the distribution of electrons in a set of orbitals of the same energy, i.e. constituents of a subshell.
- According to this rule if a number of orbitals of the same subshell are available then the electrons distribute in such a way that each orbital is first singly occupied with same spin.
- For example, the six electrons in carbon distribute as
$1{s^2}2{s^2}2p_x^12p_y^12p_z^0$ and not as $1{s^2}2{s^2}2p_x^22p_y^02p_z^0$
- Since electrons repel each other, they remain as far as possible from one another by occupying different orbitals.
There are two common ways of representing the electronic configurations. These are
a) Orbital notation method: In this notation, the subshell is represented by the respective letter symbol and the number of electrons present in the subshell is depicted, as the super script, like a, b, c, ... etc. The similar subshell represented for different shells is differentiated by writing the principal quantum number before the respective subshell.
For example, the electronic configuration of nitrogen atom (Z=7) is written as $1{s^2}2{s^2}2{p^3}$
b) Orbital diagram method: In the second notation each orbital of the subshell is represented by a box and the electron is represented by an arrow (?) a positive spin or an arrow (?) a negative spin. The advantage of second notation over the first is that it represents all the four quantum numbers.
e.g.
Al(13)= 
Electronic configurations can also be written in a short hand form. In this method the last completed orbital shell is represented in terms of a noble gas. For example, the electronic configuration of lithium and sodium can be written as
Li [He]$2{s^1}$
Na [Ne]$3{s^1}$
The electrons in the completely filled shells are known as core electrons and the electrons that are added to the electronic shell with the highest principal quantum number are called valence electrons.
