Why do beads of water form on the outside the glass of iced water on a hot day?

Those are the water vapor from the air collecting on the cold surface. The water in the air has enough energy in the molecules to keep bouncing off the other molecules in the air and stay afloat, but when they touch the cold surface of the glass they usually trade enough of their kinetic energy to let the intermolecular bond (someday I'll remember the latin name for it) take hold and they stick. As these molecules are taken out of the air more water molecules diffuse into the volume they left and the process continues until enough collect to make a good size drop. Then, as you empty the glass, they warm up again and gain enough energy to break that bond so they float away.