Question

1. Theabsorption spectra of ions have been used to identify the presenceof the elements in the atmospheres of the sun and other stars. Whatis the wavelength of light (in nm) that is absorbed byHe⁺ ions, when an electron is excited from the Bohrorbit with n = 2 to the n = 7 state? The energy of an electron inthe nth level is

En =

-

BZ2 n2

where B = 2.18 x 10^-18 J and Z = charge onnucleus (number of protons).

2. Anelectron in the 4^th energy level of the H atom drops tothe 1^st energy level. In other words an excited electrondrops to the ground state. What is the energy (in J) of the emittedphoton)? The energy of an electron in the nth level is

En =

-

B n2

=

-

2.18 x 10-18 J n2

3.The photoelectric effect for a certain alloy has a thresholdfrequency of 8.40 x 10¹⁴ Hz. For light of thisfrequency, find the energy of one mole of photons (inkJ).