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13 (2)

# 13 (2) - CHEMISTRY 121 Problem Set 13 Answers 1 Interaction...

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1 Department of Chemistry University of British Columbia Problem Set 13 Answers Interaction of Light with Matter 1. What is the energy (in J) of the 3 p z state in the hydrogen atom? The answer is: -2.42 × 10 -19 J E = J 10 2.42 3 J 10 2.18 19 2 18 × = × 2. What is the wavelength (in nm) of light emitted when the electron in a hydrogen atom moves from the 5 p orbital to the 2 s orbital? The answer is: 434 nm E = -2.18 × 10 -18 J × J 10 4.579 ) 5 1 2 1 ( 19 2 2 × = E photon = 4.579 × 10 -19 J λ = J 10 4.579 ) s m 10 (3 s) J 10 (6.626 19 1 8 34 × × × × = E hc = 4.34 × 10 -7 m = 434 nm 3. The first ionization energy of cesium is 382 kJ/mol. Calculate the minimum frequency of light (in Hz) required to ionize gas phase cesium atoms in their ground electronic state. The answer is: 9.57 × 10 14 Hz The minimum frequency of light required is that which provides energy equal to the ionization energy, since any larger frequency would necessarily provide more than the ionization energy. Frequency of light = h atom one of energy ionization h photon of energy = Hz 10 9.57 s 10 9.57 s J 10 6.626 1 mol 10 6.02 mol J 10 382 14 1 14 34 1 23 1 3 × = × = × × × × = 4. He + ions are excited to the 4 s state. These ions decay to lower energy states by one or more allowed transitions, emitting light in the process. List all these possible allowed transitions, indicating the orbitals involved (for example, a transition from the 6 s to the 5 p orbital would be specified as 6 s 5 p , rather than 6 5). Which of these allowed transitions will produce the most energetic

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13 (2) - CHEMISTRY 121 Problem Set 13 Answers 1 Interaction...

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