[WahooMan]

Hi. I need to find the oxidation number of Bromine in the compound CBr₄. I know that I need to write an equation to find the sum of the oxidation number of Carbon plus the oxidation number of Bromine plus the number of units of Bromine. But because Carbon is in group 14, I don't know whether to use +4 or -4 for its oxidation number. Which do I use, and for future reference, how do I know when to use which?

[Borek]

Simplest approach I can think of is to take a look at electronegativities. Bromine is much more electronegative, so it will suck electrons from the carbon - that means -1 for Br.

Remember that ON are artficial, they don't reflect any real (measurable) property of the atoms.