1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Calculating avg distance from nucleus

  1. Oct 15, 2009 #1
    1. The problem statement, all variables and given/known data

    Calculate the avg. distance from the Hydrogen nucleus for an electron in 2p.

    2. Relevant equations

    <r> = int[r^3 |R|^2]dr from 0->infinity

    For Hydrogen 2p, R = (1/a)^3/2 (1/(2*sqrt(sigma))*sigma*exp(-sigma/2)

    where sigma = r/a

    3. The attempt at a solution

    I get 1/4a^4 (24 a^5) = 6a but the answer's supposed to be 5a. (5a for 2p is supposed to be less than 6a, which is the avg distance for 2s.) What am I doing wrong??????
     
  2. jcsd
  3. Oct 16, 2009 #2

    gabbagabbahey

    User Avatar
    Homework Helper
    Gold Member

    That's only true when the wavefunction is spherically symmetric. In general,

    [tex]\langle r\rangle=\int_{\text{all space}}r|\psi(\textbf{r})|^2d^3\textbf{r}=\int_0^{\infty}\int_0^{\pi}\int_0^{2\pi}|\psi(\textbf{r})|^2r^3\sin\theta dr d\theta d\phi[/tex]

    That doesn't look quite right. Where did you get this from?
     
    Last edited: Oct 16, 2009
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Calculating avg distance from nucleus
Loading...