in the the periodic table in lanthanum why does the electron get filled in 5d after 6s although energy of 4f is less than that of 5d?
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Hund's Rule.
1. Electrons are assigned to orbitals in order of increasing value of (n+ℓ).
2. For subshells with the same value of (n+ℓ), electrons are assigned first to the sub shell with lower n.
In case of 5d n+l =7 and in 6s n+l=6, in 4f n+l=7,in 5d n+l= 7
1. Electrons are assigned to orbitals in order of increasing value of (n+ℓ).
2. For subshells with the same value of (n+ℓ), electrons are assigned first to the sub shell with lower n.
In case of 5d n+l =7 and in 6s n+l=6, in 4f n+l=7,in 5d n+l= 7
Arnab577:
The electronic conf. of lanthanum is ......6s2 5d1 ....whereas following the n+l rule...the configuration should have been 6s2 4f1
Some elements are more stable with less electrons in some sub-shells and more electrons in others . The 5d and 4f sub-shells have very close energies .
and hence the exception arises
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