hello sir my question is- in sequence of filling electrons after 3p why is it 4s ans not 3d?similarly after 4p why is it 5s ? plzz help

Asked by fathimaansari | 16th Sep, 2011, 12:00: AM

Expert Answer:

Electrons are filled in orbitals with lower energy and this rule is followed during filling of eletron in the orbitals.  The order of increasing of energy of orbitals can be calculated from(n+l) rule or 'Bohr bury rule'.
 According to this rule, the value of n+l is the energy of the orbital and such on orbital will be filled up first. e.g. 4s orbital having lower value of(n+l) has lower energy than 3d orbital and hence 4s orbital is filled up first. For 4s orbital, n+l=4+0=4 For 3d orbital, n+l=3+2=5,therefore 4s orbital will be filled first.

Answered by  | 16th Sep, 2011, 11:55: AM

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