## Rydberg Equation question

Marco Morales 2G
Posts: 32
Joined: Wed Sep 30, 2020 10:04 pm

### Rydberg Equation question

Is the Rydberg Equation given in the textbook (equation 2: v = R {1/n1 - 1/n2} ) the same as the equation given to us in lecture: ( En = -hR/n^2 )? I know they don't look the same lol, but it's because in one of the Sapling homework problems I had to use the the first equation, given in the book, when we never really used that equation in lecture, if I recall correctly ?

Andrew Jubintoro 3A
Posts: 56
Joined: Wed Sep 30, 2020 9:58 pm

### Re: Rydberg Equation question

You can derive the Rydberg equation from $E_n=-\frac{hR}{n^2}$
When an electron gets excited from energy level n1 to n2
\begin{aligned} \Delta E&=E_f-E_i \\ h\nu&=(-\frac{hR}{{n_2}^2})-(-\frac{hR}{{n_1}^2})\\ h\nu&=\frac{hR}{{n_1}^2}-\frac{hR}{{n_2}^2}\\ h\nu&=hR(\frac{1}{{n_1}^2}-\frac{1}{{n_2}^2})\\ \nu&=R(\frac{1}{{n_1}^2}-\frac{1}{{n_2}^2})\\ \end{aligned}
Last edited by Andrew Jubintoro 3A on Wed Oct 28, 2020 11:07 pm, edited 1 time in total.

Mohamed Mido
Posts: 56
Joined: Wed Sep 30, 2020 9:33 pm

### Re: Rydberg Equation question

I am pretty sure those are two different equations that give different results because I remember using the second one instead of the first one for a Sapling question and I didn't get the correct answer. En = -hR/n^2 gives you the amount of energy released which is why it is a negative value, while the second equation gives you frequency.

Leyna Tran 2D
Posts: 57
Joined: Wed Sep 30, 2020 9:37 pm
Been upvoted: 3 times

### Re: Rydberg Equation question

hi, those two equations are the same equations. As shown in the previous post, once you derive the En=-hR/n^2 equation, you will get v=R(1/n^2-1/n^2). You can use either one to solve problems. However, Dr. Lavelle prefers us to use the first equation because it allows us to understand the concept more than the second one.