Electronic Configuration Electronic Configuration In atomic physics and quantum chemistry, the electron configuration is the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals. For example, the electron configuration of the neon atom is 1s2 2s2 2p6. According to the laws of quantum mechanics, an energy is associated with each electron configuration and, upon certain conditions, electrons are able to move from one orbital to another by emission or absorption of a quantum of energy, in the form of a photon. Knowledge of the electron configuration of different atoms is useful in understanding the structure of the periodic table of elements. The concept is also useful for describing the chemical bonds that hold atoms together. In bulk materials this same idea helps explain the peculiar properties of lasers and semiconductors. Electronic Configuration in the Period Example :- Configuration of Li atomic number. 3, is 1s2 ,2s1
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<<--- Configuration of Be atomic no. 4, is 1s2 ,2s2 <<--- Configuration of B atomic no. 5, is 1s2 ,2s2,2p1 <<--- Configuration of C atomic no. 6, is 1s2 ,2s2 ,2p2 and so on till Neon,the last element. Note :- This addition of each subsequent electron results in a completely new configuration and as a result the chemical properties of the subsequent element change gradually. At the end of each row, a drastic shift occurs in chemical properties. Electronic Configuration in the Group From top to bottom in a column, i.e., in a group, each subsequent electron is added to the new shell, but in same sub-shell, e.g., in the 1st group, <<--- Configuration of H atomic number.1,is 1s1 <<--- Configuration of Li atomic no. 3, is 1s2 ,2s1 <<--- Configuration of Na atomic no. 11, is 1s2 ,s2,2p6 ,3s1 <<--- Configuration of K atomic no. 19, is 1s2 ,2s2 ,2p6,3s2 ,3p6,4s1 and so on till Neon, the last element. The number of valence shell electrons in an atom would determine the way it will interact with other atoms and therefore determines its chemical properties.
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Note :- Thus the outermost configuration, which is responsible for various properties such as valency, oxidation states, etc., remains same. Hence in a group, the physical and chemical properties are same. To illustrate, the halogens are strong electronegative elements. Valence Electron Configuration :- The electrons present in outer most shell of an atom which take part in chemical reactions, are known as valence electrons. These electrons can combine with valence electrons of other atom to form chemical bond. Hence valence electrons affect the chemical properties and bonding nature of an atom. The electronic configuration of outer most shell of an element is known as valence electron configuration. Itâ&#x20AC;&#x2122;s easy to write the valence electron configuration for main group elements (group 1,2 & 1318). Because the electron present in the electronic shell of highest principal quantum number are valence electron and their electronic representation will be easy. For example the electronic configuration of Cesium (Cs) is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 6s1 so that there is one valence electron in 6s and valence electron configuration will be 6s1.
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