All the matter in the universe is made of tiny particles with positive, negative or neutral charges. The positive charges are called protons, and the negative charges are called electrons. Protons are much heavier than electrons, but they both have the same amount of electric charge, except that protons are positive and electrons are negative. Because "opposites attract," protons and electrons stick together. A few protons and electrons can form bigger particles called atoms and molecules. Atoms and molecules are still very tiny. They are too small to see. Any big object, like your finger, has more atoms and molecules in it than anyone can count. We can only estimate how many there are. 