We've decided to introduce a new, intermittent series to the Chandra blog. From time to time, we'll dig into our vast archive of questions submitted by the public and post the answers written by experts at the Chandra X-ray Center. Some of these will be Chandra-specific or at least X-ray astronomy related. Others, well, they'll be somewhat random. Enjoy.
I quote from http://chandra.harvard.edu/photo/2000/0170/index.html "The Roman numerals refer to how many electrons have been stripped from the atoms. e.g. OVIII is an ion that has lost 7 electrons from its atomic shell, NeX has lost 9 electrons, etc." This does not makesense. Do you mean OVIII has lost eight electrons and NeX has lost ten?
Blame it on the Romans for not inventing zero. The neutral atoms, with zero electrons removed are labeled with I. For example HI for a neutral hydrogen atom, OI for a neutral oxygen atom, etc.
More Q&A in Resources: http://chandra.harvard.edu/resources/faq/