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To describe position & energy of electron in an atom, 4 no are required which are known as quantum no.
1)principal quantum no
2)azimuthal "   "
3)magnetic ''    ''
4)spin  ''    ''
The rules of e- configuration are
1)each orbit can accomodate a fixed no of e-  Max no of e- in an orbit is 2n²
2)e- are filled in increasing order of energy i.e. K<L<M<N
3)in the outermost shell of an atom, the max no of e- is 8 (octet) except in the first shell which can have the most 2 e- (duplet)
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The Quantum numbers are nothing but the term that is used to address the position of an electron in an atom.There are 4 quantum numbers.
It is the basic which is used to represent ORBITS or ENERGY,m,n,o
It describes the presence of ORBITALS in every,p,d,f
It represents the presence of ORIENTATION in every,py,pz
It represents the two direction of spin by an electron.
It is based on HUND'S RULE of maximum multiplicity.
The rule states that while allowing electrons into each orbitals of p.If you have to fill 3 electrons in p orbitals you can fill each one at px,py and pz.If you have to fill the fourth electron then you should put it onto px orbital which already have an electron in it.So it must be compulsary that for you to fill atleast one at each.
The diagram will make you know the configuration better way.

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