When Miss Acid told her husband, Mr Alkali, she was pregnant...
He exploded with anger.
It wasn't the reaction she was hoping for.
Funny chemistry puns always get a good reaction.
You're like an exothermic reaction, you spread your hotness everywhere!
A patient came to the ER with a rash. I told her it was an allergic reaction and that I'd prescribe her steroid cream. She asked me if she'd be discharged soon.

She was really itching to get out of here.
I'd tell you a chemistry joke but I know I wouldn't get a reaction.