Atomic Structure & the Periodic Table

Everything in chemistry follows from the structure of the atom and how electrons are arranged.

Sub-atomic particles

Proton: relative mass $1$, charge $+1$ — in the nucleus.
Neutron: relative mass $1$, charge $0$ — in the nucleus.
Electron: relative mass $\tfrac{1}{1840}$, charge $-1$ — in shells around the nucleus. The atomic number $Z$ is the number of protons; the mass number $A$