Two atoms walk out of a bar. They get half-way down the street before one says, "Wait, I left some electrons in the bar." the other says, "Are you sure?" to which he replies, "Yeah, I'm positive."
So 3 drops by 5's place to find him distraught. Upon question, 5 says, "Well, I bought 2 pets but I don't know what to name them." to which 3 says, "Well give me 1 and we'll call it even."