The Nuclear Atom

Every sample of matter you can touch is built from atoms, and every atom shares the same basic architecture: a tiny, dense central nucleus surrounded by a much larger region occupied by electrons. The nucleus contains two kinds of particle, protons and neutrons, which together are called nucleons. Protons carry a relative charge of $+1$ and a relative mass of $1$, while neutrons are electrically neutral and also have a relative mass of about $1$. Electrons occupy the space around the nucleus, carry a relative charge of $-1$, and have a mass roughly $1/1836$ that of a proton. Because electrons are so light, essentially all of an atom's mass is concentrated in the nucleus, yet the nucleus occupies only a vanishingly small fraction of the atom's volume. If an atom were scaled up to the size o