[[Modern Physics]]
# Summary
* Atoms have a small positive nucleus made of protons and neutrons and are usually surrounded by electrons.
* Nuclear notation: $^A_ZX$, Z protons A mass X atomic symbol 
* Ion is atom with net charge.
* In Bohr model, Coulomb force between nucleus and electrons provides centripetal force for circular orbit: $F_e=k\frac{q_1q_2}{r^2}$ supplies $F_{net}=m\frac{v^2}{r}$ 
* Circumference must equal a whole number of de Broglies wavelength: $n\lambda=2\pi r$
* Atomic structure here is only defined as energy levels, no probability functions yet.