![]() ![]() So in general, the probability for small separations of the two electrons is smaller than for a symmetric space wavefunction. The probability is the square of the wavefunction, and from a simple functional point of view, the square of an antisymmetric function must go to zero at the origin. An anti-symmetric space wavefunction for the two electrons implies a larger average distance between them than a symmetric function of the same type.The wavefunction for the electrons can be written as the product of the space and spin parts of the wavefunction. This forces the space part of the wavefunction to be anti-symmetric.The total wavefunction for the electrons must be anti-symmetric since they are fermions and must obey the Pauli exclusion principle.The parallel spins make the spin part of the wavefunction symmetric.It is observed that the orthohelium states are lower in energy than the parahelium states. An electron in an upper state can have spin antiparallel to the ground state electron (S=0, singlet state, parahelium) or parallel to the ground state electron (S=1, triplet state, orthohelium). In the helium energy level diagram, one electron is presumed to be in the ground state of a helium atom, the 1s state. Why do levels vary with orbital quantum number? One electron is presumed to be in the ground state, the 1s state. The electron energy levels for a helium atom demonstrate a number of features of multi-electron atoms. ![]() Helium Energy Levels Helium Energy Levels ![]()
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