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Atomic Configuration

November 5, 2012

In an atom,the electrons are arranged in in different shells and orbitals in increasing level of energy.

First they are placed in the K, then L,M,N and so on.

Inside the shells also they are arranged in sub-shells or orbitals with in increasing level of energy.

i.e.First in s, then p,d,f etc.

This arrangement is called as atomic configuration.
Atomic Configuration in a Group

From top to down 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 determine its chemical properties.

Thus the outermost configuration ,which is responsible for various properties as valency,oxidation states etc. remains same. Hence in a group, the physical and chemical properties are the same. To illustrate,the halogens are strong electronegative elements.

Atomic Configuration in a Period

e.g Configuration of Li atomic number. 3, is 1s2 ,2s1

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.

This addition of each subsequent electron results in a completely new configuration and as such the chemical properties of the subsequent element change gradually..At the end of each row, a drastic shift occurs in chemical properties.

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