[shortstuff001]

What is the formula for copper (II) sulfide? And why? Same with lead (II) bromide? I don't understand this and I'm getting different answers everywhere I turn.

[rwinterton]

Copper (II)) sulfide is CuS -- Copper monosulfide - Wikipedia, the free encyclopedia

Lead (II) bromide is PbBr2 -- Safety (MSDS) data for lead bromide

If you look up copper sulfide, you'll probably find a lot of mixed sulfides (mixtures of copper (I) sulfide and copper (II) sulfide). So it will be written Cu x S y where the x and y are subscripts composed of small numerals.

Sulfide is S -2. Copper(II) is Cu +2. You only need one sulfide to satisify the charge (and valence) of the copper.

Lead (II) is Pb +2. Bromide is Br -1 so you need two bromides to satisify the charge (and valence) of the lead.

[shortstuff001]

Copper has one valence electron and sulfur has six valence electons right? So you would need 2 coppers to satify sulfur need for eight so why isn't copper (II) sulfide written Cu2S? If copper (II) sulfide is CuS than what would copper (I) sulfide be?

[rwinterton]

The rigid and simplistic rules of valence electrons don't tell the full story. Electrons can be promoted to different levels andt his changes the number of valence electrons that it can accept or donate.

In this case, I think "charge" is a better predictor of what will be. Think of it like this: Copper (I) is Cu +1. Copper (II) is Cu +2. Sulfide is S -2. How do you balance the charge? If it's copper (I), you need to positive charges to balance the two negative charges on the sulfur. If it's copper (II) (copper is oxidized further), you need only one copper (with two positive charges) to balance the two negative charges of the sulfide). (Actually, Copper (II) is more stable and more common than Copper (I)).

There are two copper sulfides, cuprous sulfide (copper (I) sulfide) and cupric sulfide (copper (II) sulfide). Copper (I) sulfide is Cu2S. Copper (II) sulfide is CuS.