Summary
Highlights
Atoms themselves are made of even smaller particles. In the center is the nucleus, composed of protons (positive charge) and neutrons (no charge). Electrons (negative charge) orbit rapidly around the nucleus.
Atoms are the fundamental building blocks of all matter, whether solid, liquid, or gas. They are incredibly tiny; it would take one million atoms lined up to equal the width of a piece of paper.
Protons have a positive charge (+1), electrons a negative charge (-1), and neutrons are neutral (0). Opposite charges attract, preventing electrons from flying away from the atom as they are attracted to the protons in the nucleus. Neutrons help keep the particles in the nucleus together.
The mass of subatomic particles is measured in Atomic Mass Units (AMU). Protons and neutrons each weigh approximately 1 AMU. Electrons are significantly smaller, weighing only about 0.000549 AMU, and are often negligible when calculating an atom's total mass.
The visual representation of electrons orbiting in neat circles is an oversimplification. Electrons move much more randomly and rapidly around the nucleus. Additionally, atoms are mostly empty space; if a nucleus were the size of a grape, its electrons would be almost a mile away.