What are the formulas for lithium bromide?

Question

http://www.webelements.com/webelements/compounds/text/Li/Br1Li1-7550358.html

where can i find the formula for cupric nitride,and magnesium chloride also. and what are the formulas for the compounds formed by Fe2+,Cl- how do you figure this out?

You can find the formulas for cupric nitride and magnesium chloride at the same site, although cupric nitride may be harder. I believe that is Cu3N2. The two iron chlorides are FeCl2 and FeCl3.
How do you figures out FeCl2 and FeCl3. You know Cl^- is minus 1 (-1) from your question. Since each compound must be neutral, then Fe+2 and 2Cl^- would make +2 and -2 and that is neutral so FeCl2 is the formula. Fe+3 takes 3 Cl^- to make it neutral (+3 and -3) and the formula is FeCl3.