How do you write the formula for barium chloride?
So we have Barium as
Now let's move to Chloride. Don't bother looking at the table, because it is not listed. Chloride is an ion of Chlorine, which is from Group 7A and we know anything in that column has a charge of -1. So Chlorine has gained an electron and becomes Chloride. Note that this is an anion and has a negative charge. You can see how easy it was to change the name, you just change the suffix to -ide.
So we have Chloride as
We're not finished though! The charges do not balance!
To balance it we simply add another Chloride so that you have two negatives balancing the two positives. You'll write it as
Now they balance; you have one barium
The final formula is written as
Hope that helps!