How to Calculate the Mass of a ^{14}N Atom?

[WolfOfTheSteps]

Homework Statement

What is the de Broglie wavelength of an $^{14}\mbox{N}$ atom that has been laser cooled to a temperature of T=77K.

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.

 

[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).

 

[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?

 

[hage567]

Yeah, that's technically true, but I really don't think it's going to make any significant difference in your calculation.

Read this http://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=&ascii=html&isotype=some

 

[chemisttree]

Use 14.000000000000000000000000 g/mol.

Pretty easy, huh?

 

[Borek]

Use 14.000000000000000000000000 g/mol.

Pretty easy, huh?

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.

 

[chemisttree]

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.

Borek
--
General Chemistry Software
www.pH-meter.info/pH-electrode

HA! You got me there!