Do you have anything that puts a pokemon to sleep? Hypnosis or sleep powder? Ralts eventually learns hypnosis if you have one, but I can't remember what level it does.
You can ask us about what's good, too. Bulbapedia's a great resource too.
No, I have nothing that has sleep yet, and I have a Ralts in my group (I call him Melonhead, secretly, he doesn't know) but he didn't learn hypnosis yet.
I've read that I can try just throwing a Great Ball at the Abra. We'll see. Otherwise I'll go back. I'm just hesitant to move on before I caught everything.