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Electron Configuration
The Bohr’s atomic model introduced
the concept of quantum number n = 1, 2,
3, … that states the orbit or atom shell. An
atom shell can have more than one
electrons in atom shell can have more than
one electron. The arrangement of
electrons in atom shells is known as
electron configuration. Here you will
learn electron configuration for atoms of
Figure 11. electron configuration in shells
elements Z = 1 until Z = 20.
Atom shells n = 1, n = 2, n = 3, … are named shell K, L, M, …. In general, the electron
configuration for atoms of elements Z< 20 follows the following rules:
a. Filling the electrons start from the lowest level of energy, i.e shell K.
b. Shell K can hold a maximum of 2 electrons, while shells L and M can hold a maximum
of 8 electron.
c. For atoms of the elements Z = 19 and Z = 20, filling the electrons is until shell N.
Self Practice
Draw the electron configuration of atoms belonging to the elements below :
a. Nitrogen, Z = 7
b. Neon, Z = 10
c. Aluminium, Z =13
Valence Electron
The electron configuration on the outer shells plays an important role in determining
the element’s chemical properties. Electrons in the outer shell are called valence electron.
Elements with identical number of valence electron have similar chemical properties.
Figure 12. Valence electron of K element
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