What Exactly Is an Atom and Why Does It Matter?

Every atom is a tiny building block of matter, so small that millions could fit on the head of a pin.
Atoms are made up of three main parts: protons, neutrons, and electrons.
Protons give atoms their identity—hydrogen has one, carbon has six, oxygen has eight.
Electrons whirl around the nucleus in energy levels, driving chemistry and bonding.
Neutrons add stability to the nucleus, balancing the positive charge of protons.
Atoms combine to form molecules, creating everything from water to DNA.
Most of an atom is empty space, despite making up all the solid stuff around us.
The number of protons in an atom defines its place on the periodic table.
Chemical reactions are simply atoms rearranging their bonds to form new substances.
Without atoms, there would be no matter—no stars, no Earth, no life itself.