Use a master ball on it.
There are many reasons that you might not be able to catch Zapdos. You should try putting him to sleep before attempting to capture.
Can't catch zapdos in sapphire
You can only catch Zapdos in Crystal by cheating. otherwise it is not in the game
to catch zapdos in pokemon black you have to have every legendary pokemon
You can catch Zapdos at the Power Plant in the Kanto Region You have to have all 16 badges. I would suggest using Fast Balls. If that doesn't work, try Ultras. :D Hope this helped!
catch Zapdos or Articuno
If you need a good electric-type Pokemon catch ZAPDOS. to catch him you need to surf in route 10 from ROCK TUNNEL to POWER PLANT. inside of power plant is zapdos. be sure to have an ultra ball and don't forget to save the game before try to catch him. if you can't catch zapdos you beter get a pikachu than an electrode.
To catch Zapdos you have to go to the power plant in Pokemon blue you also might need lots of poke balls because zapados is really hard to catch also try and and put him to sleep or paralyze him or freeze him and lower down his health so its easier to catch him.
Some times it really takes awhile legendary Pokemon such as zapdos are very difficult to capture at times if you saved before trying to catch it you can reset or turn off the game and when you reopen your file you can retry to catch it, if nothing seems to be working try using timer balls or get a zapdos from someone else.
Zapdos is one of greevills shadow Pokemon catching it is no easy task the best way to capture it is to eliminate all of greevills other Pokemon that way zapdos is the only one left and then use this strategy: Weaken it as far as you can and try to paralyze it or make it go to sleep then use lots of timer balls they usually work on zapdos for some reason.
Both games can't get zapdos so trade one from firered, leafgreen or xd gale of darkness.
you might not be able to catch a zapdos in those games but if you have fire red you can catch him at the power plant once you have surf and then transfer it on to your other game.