Begin the discussion by explaining the atom -- both its function and parts. Atoms form all physical objects in the universe and are made up of positively charged protons, negatively charged electrons, and neutrally charged neutrons. Different materials can have negative, positive or neutral charges, depending on the charges of the atom make-up. When opposite charges come together they are attracted. Static electricity adds negative charges to the surface of an object, which causes a reaction against positively charged materials.
Create a pile of salt and pepper on a center desk, and ask the children how long it would take to remove the pepper from the salt pile. Ask the students how they might expedite the process and what tools they might use. Discuss whether or not they think static electricity might help to separate the spices. Have the children form a hypothesis, whether it is that static electricity can help to move the spices apart, or that it can't. Let them decide which hypothesis they want to go with.
Have the children gather around the center desk, and mix the salt and pepper together well with a spoon. Rub an inflated balloon on your head or sweater, and show the students how your hair moves with the balloon after it is charged with static electricity. Move the balloon slowly to the salt and pepper and hold it a few inches over the plate. Keep inching the balloon closer until the pepper jumps up and attaches to the surface of the balloon. Both spices are attracted, but the pepper is lighter so it moves before the salt.
Ask children what they noticed when you rubbed the balloon against your head or sweater and how it happened. If they don't guess correctly, explain that when you rub the balloon, you give it a negative charge. Discuss the ability of static electricity to move the pepper due to the negative charge introduced to the surface of the balloon by the static electricity, and the positive charge of pepper. Ask the students what charges exist in an atom and which charges attract or repel. Objects with the same charge repel each other, while the different charges attract each other. This is how the balloon was able to move the pepper.