How do you know what the charge is for a compound so you can draw a lewis structure?

Question

How come the charge is 3+ for BrF2? How do you come to that conclusion?

What is the charge for SeBr4?

Answer 1

Does that ion really has charge +3 ?

I think it is -3

To know the charge on ions you should know the positions of the atoms in the periodic table.

F,Cl, Br,I, all occur in the 17th column of the periodic table.

So they carry -1 charge because they have high tendency to gain electron to have their octet structure.(they need 1electron to have octet structure )

In the BrF2 ion both Br&F carry -1 charge since there are 2F total charge is -3

So I think it is BrF2-3 and not BrF2+3(though I am not sure because these type of ions are rare and molecules like BrF3&BrF5 are common though they are not ions)

About SeBr4 does it has any charge?