HaHa. I love atom/science jokes.
A proton, neutron, and electron went out to dinner one night. After a luxurious meal, the waiter brought the check to the proton and the electron. The neutron was perplexed as to why the waiter didn't bring him his check. So, he summoned the waiter to the table and asked him about it.
The waiter explained to the neutron, "For you, there's no charge!"