By Hund’s rule, the electron configuration of carbon, which is 1 s 22 s 22 p 2, is understood to correspond to the orbital diagram shown in c. Hund, 1896–1997), which today says that the lowest-energy electron configuration for an atom is the one that has the maximum number of electrons with parallel spins in degenerate orbitals. (named after the German physicist Friedrich H. Choice c illustrates Hund’s rule A rule stating that the lowest-energy electron configuration for an atom is the one that has the maximum number of electrons with parallel spins in degenerate orbitals. Similarly, experiments have shown that choice b is slightly higher in energy (less stable) than choice c because electrons in degenerate orbitals prefer to line up with their spins parallel thus, we can eliminate choice b. List all the allowed combinations of the four quantum numbers ( n, l, m l, m s) for a 6 s orbital, and predict the total number of electrons it can contain.Īnswer: (6, 0, 0, +½), (6, 0, 0, −½) two electronsīecause of electron-electron repulsions, it is more favorable energetically for an electron to be in an unoccupied orbital than in one that is already occupied hence we can eliminate choice a. There are only three possible combinations of ( n, l, m l): (2, 1, 1), (2, 1, 0), and (2, 1, −1).ī Because m s is independent of the other quantum numbers and can have values of only +½ and −½, there are six possible combinations of ( n, l, m l, m s): (2, 1, 1, +½), (2, 1, 1, −½), (2, 1, 0, +½), (2, 1, 0, −½), (2, 1, −1, +½), and (2, 1, −1, −½).Ĭ Hence the 2 p subshell, which consists of three 2 p orbitals (2 p x, 2 p y, and 2 p z), can contain a total of six electrons, two in each orbital. List all allowed combinations of ( n, l, m l).ī Build on these combinations to list all the allowed combinations of ( n, l, m l, m s).Ĭ Add together the number of combinations to predict the maximum number of electrons the 2 p subshell can accommodate.Ī For a 2 p orbital, we know that n = 2, l = n − 1 = 1, and m l = − l, (− l +1),…, ( l − 1), l. List all the allowed combinations of the four quantum numbers ( n, l, m l, m s) for electrons in a 2 p orbital and predict the maximum number of electrons the 2 p subshell can accommodate.Īsked for: allowed quantum numbers and maximum number of electrons in orbitalĪ List the quantum numbers ( n, l, m l) that correspond to an n = 2 p orbital. With this information, we can proceed to construct the entire periodic table, which, as you learned in Chapter 1 'Introduction to Chemistry', was originally based on the physical and chemical properties of the known elements. Because m s has only two possible values (+½ or −½), two electrons, and only two electrons, can occupy any given orbital, one with spin up and one with spin down. He developed the Pauli exclusion principle A principle stating that no two electrons in an atom can have the same value of all four quantum numbers.: No two electrons in an atom can have the same values of all four quantum numbers (n, l, m l, m s ).īy giving the values of n, l, and m l, we also specify a particular orbital (e.g., 1 s with n = 1, l = 0, m l = 0). The implications of electron spin for chemistry were recognized almost immediately by an Austrian physicist,Wolfgang Pauli (1900–1958 Nobel Prize in Physics, 1945), who determined that each orbital can contain no more than two electrons.

Electrons have two possible orientations (spin up and spin down), which are described by a fourth quantum number ( m s). This magnetic moment is called electron spin The magnetic moment that results when an electron spins. Although the electron cannot be viewed solely as a particle, spinning or otherwise, it is indisputable that it does have a magnetic moment.

When an electrically charged object spins, it produces a magnetic moment parallel to the axis of rotation, making it behave like a magnet. In 1925, two graduate students in physics in the Netherlands, George Uhlenbeck (1900–1988) and Samuel Goudsmit (1902–1978), proposed that the splittings were caused by an electron spinning about its axis, much as Earth spins about its axis. Scientists also discovered that applying a magnetic field caused the lines in the pairs to split farther apart.

Because each line represents an energy level available to electrons in the atom, there are twice as many energy levels available as would be predicted solely based on the quantum numbers n, l, and m l. When scientists analyzed the emission and absorption spectra of the elements more closely, they saw that for elements having more than one electron, nearly all the lines in the spectra were actually pairs of very closely spaced lines.

Krypton orbital diagram