# Homework Help: Very easy atomic weight problem

1. Apr 14, 2007

### WolfOfTheSteps

1. The problem statement, all variables and given/known data
What is the de Broglie wavelength of an $^{14}\mbox{N}$ atom that has been laser cooled to a temperature of T=77K.

3. The attempt at a solution

This is a trivial problem, and I can do the physics... But how do I calculate the mass of $^{14}\mbox{N}$? My chemistry is obviously less than crappy.

Thanks.

2. Apr 14, 2007

### hage567

You can look up the mass on a periodic table, it gives the mass in g/mol, where one mol contains 6.02x10^23 atoms (Avogadro's number).

3. Apr 14, 2007

### WolfOfTheSteps

I know that much, but what does the 14 do in $^{14}\mbox{N}$. I know that the 14 is the "mass number." So, surely $^{14}\mbox{N}, ^{15}\mbox{N}, ^{16}\mbox{N},$ etc have different masses, and you can't just use the mass that's on the periodic table.

Isn't this true? In that case, how do I take the 14 into account?

4. Apr 14, 2007

### hage567

5. Apr 16, 2007

### chemisttree

Use 14.000000000000000000000000 g/mol.

Pretty easy, huh?

6. Apr 16, 2007

### Staff: Mentor

Probably as wrong as easy... Not that it matters much, but 14N mass is not 14.0000. 12C is 12.0000, mass deficit per nucleon for nitrogen is slightly different.

7. Apr 18, 2007