# Physics with Calculus/Modern/Atoms

### Atoms

The atom was, until comparatively recently, thought to be the fundamental building block of matter, and for the purposes of this textbook, we will treat it as though it were.

The atom consists of three types of particles: the electron, the proton, and the neutron.

The protons and the neutrons are contained within a very small amount of volume in the center of the atom called the nucleus. Protons have a net positive charge of 1 e, where e is the fundamental unit of charge, equal to about $1.6\times 10^{-19}$  coulombs. Neutrons have no net electric charge and are very slightly more massive than a proton.

Electrons are in orbit around the nucleus of the atom, and have a net negative charge of -1e. Their mass is much less than that of the proton and neutron, and so the electrons are generally left out when determining the mass of an atom.

The electrons are, in microscopic terms, astonishingly distant from the nucleus. If we take a hydrogen atom (1 electron and 1 proton) to be about an angstrom in diameter (1 angstrom is $10^{-10}$  meters), then the approximate diameter of the nucleus is $10^{-15}$ m. In more familiar terms, if the nucleus was an inch in diameter, the first electron would be about 830 feet away.

Masses

Proton: $1.6726\times 10^{-27}$ kg

Neutron: $1.6749\times 10^{-27}$ kg

Electron:$9.1094\times 10^{-31}$ kg

Charges

Proton: +1e

Electron:-1e

Neutron: 0

where e=$1.6022\times 10^{-19}$ C