Unlike the hydrogen atom, in the case of the helium atom the energy is quantized by two quantum numbers (not just the primary quantum number n as is the case for H). This is due to
(a) Hydrogen forms a diatomic molecule unlike He
(b) He is a larger atom
(c) He has more electrons
(d) He has a complete 1s shell
Answer,-
(d) He has a complete 1s shell
Explanation -
He is quantized by two quantum numbers because of its completely filled 1s shell consisting of
two electrons. Thus , under the situation besides n ,( the principal quantum number ) , the spin quantum
number ( s ) identifying axial motion of the two electrons separately in He atom becomes essential; ie.
1 s2 where , n = 1 & s = +1/2 , -1/2
In case of H :- since there is only one electron in the orbit ( major energy level ), the only electron has
one and the same type of axial motion , so no other quantization is necessary to be given.
In both the cases ; l = 0 & m = 0 , so need not be given .
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