```
r = n^2 * h^2 / (2 * pi * m * k * e^2)
```
where:
* r is the radius of the orbit in meters
* n is the principal quantum number, which can take on any positive integer value
* h is Planck's constant (6.626 x 10^-34 J s)
* m is the mass of the electron (9.11 x 10^-31 kg)
* k is the Coulomb constant (8.99 x 10^9 N m^2/C^2)
* e is the elementary charge (1.602 x 10^-19 C)
The energy of an electron in an orbit is given by the formula:
```
E = -13.6 eV / n^2
```
where:
* E is the energy of the electron in electron volts (eV)
* n is the principal quantum number
As the principal quantum number n increases, the radius of the orbit increases and the energy of the electron decreases. The lowest energy orbit is the n = 1 orbit, which is called the K shell. The next energy orbit is the n = 2 orbit, which is called the L shell. And so on.
Each electron in an atom occupies a specific orbital, which is defined by the three quantum numbers: the principal quantum number n, the angular momentum quantum number l, and the magnetic quantum number m. The n quantum number determines the energy of the orbital, the l quantum number determines the shape of the orbital, and the m quantum number determines the orientation of the orbital in space.
The electrons in an atom fill up the orbitals in a specific order, called the Aufbau principle. The lowest energy orbitals are filled first, and then the electrons move into higher energy orbitals as the atom becomes more complex.
The electron configuration of an atom is a description of the number and arrangement of electrons in the atom's orbitals. The electron configuration can be used to predict the atom's chemical properties.
