# Homework Help: Wavelength HELP

1. Dec 13, 2011

### CDerhammer

Wavelength HELP!!!!

1. The problem statement, all variables and given/known data
Calculate the wavenumber (v=1/lambda) and the wavelength of the first transition in the visible region of the atomic spectrum of hydrogen.
I KNOW THE ANSWER..... 656.3 nm. I just don't have a clue how they got that answer, I do know that I had to use Rydberg's Constant (1.097X10^7 m ^-1) but I have no idea what to do or how to do it. Thank you anyone who wants to take time and help me. And I don't know if this will mean anything but it is Inorganic Chem 430.

2. Relevant equations
1/λ=R(1/n12-1/n22)

3. The attempt at a solution
I have been at this for hours trying to find out how to calculate everything. and IDK if it's my ti-84 plus edition that is doing the math wrong or what but I cannot find out how to compute this....
1. The problem statement, all variables and given/known data
No variables were given to me except rydberg's constant.

2. Dec 13, 2011

### netgypsy

Re: Wavelength HELP!!!!

If you Google the first transition for hydrogen you get from 3 to 2 for your n values.

From there just put the numbers into the equation, evaluate the right side and take the reciprocal to get the wavelength.

3. Dec 13, 2011

### sandy.bridge

Re: Wavelength HELP!!!!

Look at the atomic spectrum for hydrogen. There are only four lines. Which values of "n" will you be using for the first transition?

4. Dec 13, 2011

### CDerhammer

Re: Wavelength HELP!!!!

Okay, Now i get 1/λ=1.097x107m-1(1/6) am I on the right track?

5. Dec 13, 2011

### CDerhammer

Re: Wavelength HELP!!!!

my book says it starts at n=2 and n2≥3

6. Dec 13, 2011

### netgypsy

Re: Wavelength HELP!!!!

1/2squared - 1/3squared does not equal 1/6 . You'll get 1/4 - 1/9 =5/36, not 6/36 otherwise you're doing it right. You just had to figure out what the n values were for that first transition which as I said, I asked Google and it said from 3 to 2.

7. Dec 13, 2011

### CDerhammer

Re: Wavelength HELP!!!!

Whoops yeah, I meant 5/36. then I get 1/λ=1523611.111m-1
lol, sorry if I am bugging you but what do I do now to convert it to nm? Particularly 656.3 nm... lol

8. Dec 13, 2011

### netgypsy

Re: Wavelength HELP!!!!

If you google nanometer you will see that 1 nm is 10 ^ -9 meters :-)

You found 1/lamda You need to take the reciprocal to get lamda, the wavelength. Than change it to nanometers.

9. Dec 13, 2011

### CDerhammer

Re: Wavelength HELP!!!!

Hmm... I am not too sure how to get the number 656.3 though. Im fine with converting. Just can't find the 656.3

10. Dec 13, 2011

### netgypsy

Re: Wavelength HELP!!!!

When you solve the equation you'll get 1/lamda = 5/36 (1.097 X l0^ 7)

flipping the whole thing over you'll get lamda = 36/5divided by 1.097 X 10 ^7

which is pretty close to 7 divided by 1.1 X 10 ^ 7 which you can see by estimating is 6 something X 10 -7 it will come out the right answer.

11. Dec 13, 2011

### CDerhammer

Re: Wavelength HELP!!!!

Wow. The book says nothing about flipping everything. got the answer perfectly. Thanks!
*I MUST REMEMBER TO FLIP EVERYTHING!

12. Dec 13, 2011

### netgypsy

Re: Wavelength HELP!!!!

There are quite a number of equations in physics that allow you to find the reciprocal of quantities and whenever the thing you are looking for is in the denominator like with 1/lamda, you have to calculate the number part and then take the reciprocal to get the thing you want, lamda. And one of the easiest ways to do that is to just flip the whole thing over on both sides (but be careful because you can NOT flip the sum of two fractions. You have to first get a common denominator, add, then flip.

13. Dec 13, 2011

### CDerhammer

Re: Wavelength HELP!!!!

Well this is going to be a long journey through my inorganic chem 430 class lol. How come I couldn't find this stuff on youtube or google or anything?

14. Dec 13, 2011

### netgypsy

Re: Wavelength HELP!!!!

It's on there. I found the n values on google. You would get that same problem in physics, in several different areas. I never took inorganic. LOVED Physical chem and instrumental analysis.

15. Dec 13, 2011

### CDerhammer

Re: Wavelength HELP!!!!

Yeah I'm a biochem major at Indiana University, I have physical chem 362 coming in the spring. but I am only a freshman lol

16. Dec 13, 2011

### netgypsy

Re: Wavelength HELP!!!!

Good luck and enjoy. I could have stayed in college forever. Sooo much fun. so many interesting people.

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