Randal Corliss, age 9, of Portland, Maine for his question:
How big is a proton?
Picture a towering building made of ordinary bricks. If an atom were as big as the building, the protons inside it would be about as big as the bricks. Atoms, of course, come in different sizes, but even the strongest microscope can photograph only their tiny shadows. It takes a row of about 100 million medium sized atoms to measure one inch. It would take a row of at least 100,000 protons to reach across the width of even the smallest atom.
Everything we touch is made of matter and matter is made of tiny packages that are too small for our eyes to see. A molecule is a package of atoms. An atom is a neat package of tiny units of matter called particles. They have electric energy to do certain things. Every proton particle in the world is alike. It has one charge of positive electricity. Every electron particle has a matching charge of negative electricity.
An atom keeps all its protons in a tight fisted core called its nucleus. Its negative electrons are free to swarm like bees around the nucleus. The smallest atom has one positive proton and one negative electron. In larger atoms also, the number of protons in the nucleus is balanced by the same number of orbiting electrons.
For example, this iron atom has 26 protons and 26 electrons. A row of about 100 million of these iron atoms measure one inch. Now imagine a fly in a movie house ¬because most of an atom is empty space. It is about 100,000 times wider than the nucleus. And inside the iron nucleus there are 26 protons, plus a swarm of other particles. To make a row one inch long, we would need to line up 4 million million protons. This enormous number is 4 plus a tail of 12 zeros which is more than you could count in a whole life time.
Look at one crystal of ordinary salt. Actually it is a neat openwork lattice of molecules. The number of molecules in that small salt crystal is roughly 10 plus 24 zeros. And inside each of those teeming molecules there are exactly 28 proton particles.
The size of a proton strains the imagination. As a rule, scientists measure it by its weight, which they call its mass, and by its charge. For example, a proton's positive charge exactly balances the opposite negative charge of one ,electron. But the proton is 1836 times more massive than the electron. Nobody has ever seen a proton or electron. But from indirect evidence, scientists think that the lightweight electron may be a bit larger than the more massive proton.
Protons happen to be the most important atomic particles. An atom can, and often does, lose electrons. But if it loses or gains a proton it becomes a different atom. This explains why the chemical elements have atomic numbers. Every iron atom must have 26 protons, so the atomic number of iron is 26. The smallest atom is hydrogen. It has only one proton, so naturally atomic number 1 belongs to hydrogen.