Atomic Structure and the Nuclear Model

Every sample of ordinary matter is built from atoms, and every atom shares the same basic architecture: a tiny, dense central nucleus surrounded by a cloud of electrons. The nucleus contains two kinds of particles, collectively called nucleons. Protons carry a positive charge of $+1.6 \times 10^{-19}$ C, while neutrons carry no charge at all. Electrons orbit outside the nucleus and carry an equal but opposite negative charge, $-1.6 \times 10^{-19}$ C. Because a neutral atom has equal numbers of protons and electrons, the atom as a whole is electrically neutral. The proton and neutron have almost the same mass, roughly $1.67 \times 10^{-27}$ kg, whereas the electron is about 1836 times lighter. This means nearly all of an atom's mass is concentrated in the nucleus, even though the nucleus o