Comparison of the Bohr and Quantum Mechanical Models of the Atom
1. The electron is treated mathematically as a wave in the Quantum Mechanical model but as a particle in fixed orbits around the nucleus in the Bohr Model. The electron has properties of both particles and waves.
2. In the quantum mechanical model, the electron can be very close to the nucleus or very far away.
The probability of the electron being a certain distance from the nucleus most of the time is high
90% (0.529 A for the hydrogen 1s electron).
3. In the Bohr model, the energy of the electron is described in terms of a definite orbit. In the quantum mechanical model the energy is described in terms of the probability of locating the electron in a region of space outside the nucleus called an orbital.
4. In the quantum mechanical model, energy levels are thought of as clouds surrounding the nucleus and not fixed orbits.
5. The quantum mechanical model gives information about the location of an electron in an atom, regarding its energy level, sublevel, orbital, and spin. Every electron has a set of four quantum numbers, with no two electrons having the same set of four numbers.
Electron Configurations
Quantum Mechanical Model:
Quantum Numbers: numbers used to give information about the location of an electron in an atom with respect to its energy level, sublevel, orbital, and spin. Every electron has a set of four quantum numbers. No two electrons have the same set of four quantum numbers.
1.
Principle Quantum Number (n) – indicates the main energy level (shell) surrounding the nucleus or the average distance of the electron from the nucleus. The range of “n” is 1  
.
2.
Sublevel (angular momentum) Quantum Number (l) – represents the shape of the space occupied by an electron in a given sublevel (s, p, d, f,…) of the principle quantum number
(energy level). The number of sublevels in “n” is equal to n and the range of “l” is 0 
n-1. s p d f g h…..
0 1 2 3 4 5
3.
Orbital (magnetic) Quantum Number (m l
) – represents the electron’s orientation in space along the X-, the Y-, or the Z-axis. There can be a maximum of only two electrons occupying any one oribital. Any orbital may contain 0, 1, or 2 electrons. The number of orbitals in a main energy level is n
2
. The total number of electrons in a main energy level is
2n
2
. s sublevels contain 1 orbital, p sublevels contain 3 orbitals, d sublevels contain 5 orbital, f sublevels contain 7 orbitals,
The number of orbitals in “n” is n
2
and the range of “m” is –l

+l s p d f g
0 -1, 0, 1 -2, -1, 0, 1, 2 -3, -2, -1, 0, 1, 2, 3 -4, -3, -2, -1, 0, 1, 2, 3, 4
4.
Spin Quantum Number (m s
) – represents the direction of spin of an electron which may be either +1/2
(  )
, or –1/2
(  )
. There can be a maximum of two electrons occupying any one orbital. Single electrons have parallel spins and paired electrons have opposite spins.