I don't feel like starting a religious war on the credibility of Wikipedia and its data. I will just mention, that the actual data is from another source, as referenced in the original text: http://www.periodictable.com/Elements/014/data.html As for the equation, that actually was from Wikipedia, I mostly included the link to include some description and explanation of the theory behind it. The equation should not be new to any physicist, I hope. For people, who desire another reference, please look up the excellent book by David J. Griffiths, 'Introduction to Electrodynamics'. I can't recommend that book enough, but it seems rather over the top to order it from amazon to check a formula. The equation in question can be found on page 275 (3rd ed.) as (6.32). Satyanarayan Nagarajan wrote: > Data from wikipedia needs some care. Many times the information posted on Wiki is not moderated - so a double check is always good. > >