Zapdos has two offensive moves, both of relatively low PP. The rest
are stat boosters, which can keep it going for awhile, but gives you
a lot of time to catch it. If you exhaust it of it's two offensive
moves, you will have at least 50 turns to capture it, before it begins
to succumb to Struggle. This is assuming you're not applying pressure.
Try coming at night, so you can utilize Dusk Balls to capture the
Pokemon; increasing your chances by a fairly large amount. There is no
need to worry about it running away. Zapdos will appear again if you
defeat it by accident/on purpose, after you defeat the Champion again.
basicly beat the champion source and how to catch and get info on other legenderys here legends