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CHEMISTRY 1B.1stmidterm


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CHEMISTRY 1b, SPRING, 1996 FIRST MIDTERM EXAMINATION 1. (25 points) The energies and configurations of the ground electronic state of helium and the five lowest excited states in which the electrons are paired are given below in order of increasing energy configuration , Energy(J/atom) (1s) 2 , -3.939 x 10 -18 1s2s , -6.363 x 10 -19 1s2p , -5.398 x 10 -19 1s3s , -2.671 x 10 -19 1s3d , -2.425 x 10 -19 1s3p , -2.404 x 10 -19 o A helium atom excited to the 1s2p state emits a photon. Calculate the wavelength of the emitted photon with the highest possible energy. o Calculate the momentum of the photon whose wavelength you calculated in the first part. o Another excited helium atom in the 1s2p state absorbs a photon. Calculate the wavelength of the absorbed photon with the lowest possible energy. o In those configurations where the electrons can be either paired or unpaired, which possibility (paired or unpaired) has the lowest energy? o If one uses the principles which work so well for ground states of atoms, one of the excited states of helium appears to be out of order. Which one? Discuss the rationale
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