# The emission lines we see in a spectrum are due to

• Notes
• 3

This preview shows page 2 - 3 out of 3 pages.

The emission lines we see in a spectrum are due to changes in energy levels (stationary states). We can compute these wavelengths from Bohr's result for the energy levels of an electron in an atom E i = - 1 2 Z 2 E 2 a o n i 2 and the spectral line is given by E = E i - E f

Subscribe to view the full document.

E = 1 2 Z 2 e 2 a o ( 1 n f 2 - 1 n i 2 ) where 1 2 Z 2 e 2 a o R z or R z = Z 2 R And R is known as the Rydberg constant and is calculated with Z = 1 (hydrogen atom) R = 1 2 e 2 a o = 1 2 (1.60 x 10 -19 C) 2 (0.530 x 10 -10 m) x (9 x 10 9 J m) c 2 R = 2.18 x 10 -18 J or by using energy conversion factors: R = 109678 cm -1 = 13.60 eV = 313.6 kcal mole -1 There is one more detail - we have been working with the assumption that we know n i & n f and want to obtain E or λ - we could also perform an experiment that measures λ . Using Planck's law E = hc λ we could obtain E ( and n i , if n f is already known). All of the quantum theory we have done is applicable. You must be able to work in all possible directions using these expressions.
You've reached the end of this preview.

{[ snackBarMessage ]}

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern