Ask the volunteer to step away from the balloon, then move toward it. Have other students try this same exercise. Scientists know that lightning results from a complicated interplay of positive and negative electrical charges occurring in the 2,000 or so thunderstorms taking place on Earth at any given moment. To learn about what causes lightning, scientists had to learn about the interaction of electrons and positive ions. Electrons, tiny particles orbiting the outside of atoms, carry a negative charge.
Positive ions are atoms or molecules that have lost an electron.
Atoms and molecules normally have equal positive and negative charges, making them neutral. When different materials come in contact, electrons are transferred and one of the materials gains an excess of electrons and becomes negatively charged. When an object with a lot of positive or negative charges gets close to an object carrying the opposite charge, a spark jumps across the space between them to neutralize the charges. In a thunderstorm, that spark is a lightning bolt. It's only a couple of inches wide, but it leaps between the clouds and the earth at a remarkable 90,000 miles per second.