# Hydrogen atom data

1. Mar 14, 2014

### bobie

Can someone give me a link where I can find data on the size of an H atom (free and in main compounds like water)?
If there is none can you tell me roughly the range of sizes or at least what is the ratio between a free atom and a bound atom.
I know that for a free atom the radius is not the Bohr radius anymore , and that there is a cloud of probability, can you tell me what is the radius where probability is 95%?

If it is possible, I'd like to learn what is the official value of the magnetic field B of the ground state (1s), as on the web I found many contrasting values. I tried to calculate it myself and I got 1/8 Tesla, is that correct?
I read also that angular moment in QM is 0, is it h/2pi in classical model?
Thanks a lot for your help.

Last edited: Mar 14, 2014
2. Mar 14, 2014

### DrDu

Hydrogen atoms aren't spheres and therefore don't have a unique radius. Rather, the definition depends on the application. You may look for the term "covalent radius".
The 95% probability radius I would have to calculate myself:
If r is measured in units of a (Bohr radii) then
$\int_0^{r_{95\%} }r^2 \exp(-r)dr=0.95\times \int_0^\infty r^2 \exp(-r)dr$.
Probably, Wolfram Alpha will solve that for $r_{95\%}$.

I have never heard of the official value B field for hydrogen. Anyhow the magnetic moment vanishes both for a classical and a quantum mechnanical state with l=0, e.g. in Bohr-Sommerfeld theory.

3. Mar 14, 2014

### bobie

Thanks for the precious tip, I found r= 79 and covalent r 32
As to the magnetig moment I found 9.285 * 10^-24 J/T
If I divide that by μ which is (if I am not wrong q*v*r/2) h/4π, to I get the value of B?
As to angular momentum (mvr) I think it is twice as the magnetic moment h/2pi