Copper (I) Oxide [ENDORSED]

[NinaSheridan]

Does the roman numeral between copper and oxide mean the oxygen atom is negatively charged or the copper atom?

[vsyacoubian2A]

The Roman Numeral (I) indicates the positive charge of the metal cation. Metals are always positive, so copper will be positive. The (I) will indicate its charge, so copper will be Cu1+. Reason for the Roman Numerals is that some transition metals can have different charges (i.e. 2+ or 3+) and the numeral clarifies what the charge is.