[ General Glossary, Quantum Glossary, Atomic Glossary ]
Ion-naming Conventions

Astronomers (and others) commonly use roman numerals to specify the ionization state of an atom. The convention is that the roman numeral I is used to specify the neutral atom, II to specify the once-ionized ion (ie one electron removed), etc,etc. Thus for oxygen (atomic number, Z=8)

Symbol	Alt.Symbol	Meaning
O I	O	Neutral atoms (all 8 electrons remaining)
O II	O+	Once-ionized (7 electrons remaining)
O III	O2+	Twice-ionized (6 electrons remaining)
etc	etc	etc
O VII	O6+	"Helium-like" (2 electrons remaining)
O VIII	O7+	"Hydrogen-like" (1 electron remaining)
O IX	O8+	"Fully-stripped" (No electrons remaining)