So for this example question, it says write the formula for each of the following compounds. We have hydro iota acid, hydro sealenic acid, and hydrofluoric acid. All right, So we're going to say that hydro, we know that represents the H ion involved, so we have H+ for all of these. Since they're all binary assets, we know they all end with ick acid. What we look at is the base name. The base name tells us the nonmetal involved. So iode means we're dealing with iodine. It's in Group 7A, so it's one sillin means we're dealing with Selenium. It's in Group 6A, so it's 2- or -2 and then floor means we're dealing with fluorine, which is in Group 7A, so it is -1.
Now for the first one for a. Remember, when the numbers and the charges are the same, they simply cancel out and you combine your elements together. So hydroiodic acid is just HI. And then also for C +1 -1, the numbers are the same, so you just combine them together. So hydrofluoric acid is HF. For B hydrosalenic acid. We have here different numbers in the charges. Remember when the numbers are different they crisscross. So one from here comes here 2 from here comes here O. That means hydrocellenic acid is H2Se.
If you don't quite remember these rules, make sure you go back and take a look at our videos talking about writing ionic compounds. It's the same kind of principles behind this. We look at the ions and charges. If the numbers are the same, they simply cancel out. If the numbers are different and they crisscross, using this helped us to determine each one of these three binary acids. Now that we've done this example, move on to the next video where we take a look at a practice problem.