Bohr model of the atom

Particles have a characteristic wavelength such that

Q = particle momentum
W = particle wavelength
h = Planck's constant
  = 6.62*10^-34 Joule seconds

Q W = h              de Broglie formula
Suppose an electron orbits a proton (a hydrogen atom). According to the Bohr theory, the number of wavelengths experienced by the electron during one orbit is an integer.
R = Orbit radius
C = Orbit circumference
The Bohr assumption:
C = N W                  where N is an integer

N = 1   corresponds to the S orbital
N = 2   corresponds to the P orbital
N = 3   corresponds to the D orbital

M = Electron mass
  = 9.11*10^-31 kg
V = Electron velocity
Q = Electron momentum
  = M V
e = Electron charge
  = -1.60*10^-19 Coulombs
p = Proton charge
  = +1.60*10^-19 Coulombs
k = Coulomb constant
  = 9.0*10^9  Newtons meters^2 / Coulombs^2
Fe= Electric force
  = k p e / R^2
Fc= Centripetal force
  = M V^2 / R
For an electron in a circular orbit,
Fe = Fc
This sets the characteristic size of the hydrogen atom.
E = Electric potential energy
  = k p e / R
  = Energy required to steal the electron from the proton (the "ionization energy").