12 | The History and Use of Our Earth’s Chemical Elements “orbit” is more closely related to the image of two-dimensional concentric rings, similar to an

12 | The History and Use of Our Earth’s Chemical Elements “orbit” is more closely related to the image of two-dimensional concentric rings, similar to an

archery target. The term “energy level” describes the energy that electrons possess, depending on their distance from the atom’s nucleus. The term “orbital” is the more descriptive term and describes the original four distinct energy levels detailed in Pauli’s exclusion principle based on the angular momentum quantum numbers. Because the original four energy levels for electrons surrounding the nucleus were identified by Wolfgang Pauli and others, three more orbitals (energy levels) have been added to accommodate new artificial elements as they have been discovered. Shells, orbitals, and energy levels make up the levels of electron energy sur- rounding the nuclei. Similar to “shell,” “orbital,” and “energy level,” the notions of subshells or orbitals are used interchangeably. This electron structure is depicted by the figure for each element listed in the section, “Guide to the Elements.” The patterns for electron configuration for each of the following seven energy levels (shells or orbits) follow:

1. The first shell or energy level out from the nucleus is called the “K” shell or energy level and contains a maximum of two electrons in the “s” orbital—that is, K = s2, where the “K” represents the shell number (or principle quantum number), the “s” describes the orbital shape of the angular momentum quantum number, and the “2” is the maximum number of electrons that the “s” orbital can contain. This particular sequence is “K = s2,” which means K shell contains 2 electrons in the “s” orbital. This is the sequence for the element helium. Look up helium in the text for more information.

2. The second shell or energy level is “L” and may contain a maximum of eight electrons; its orbital is called “p” and can contain a maximum of six electrons. Therefore, its sequence would be K = 2 (s2) and L = 8 (s2 + p6). This sequence of 10 electrons in the first two shells (K and L) represents the element neon, which has an atomic number of 10.

3. The third shell or energy level is “M” and may contain a maximum of 18 electrons; its orbital is called the “d” subshell, and it may have a maximum of 10 electrons: for example, K = 2 (s2), L = 8 (s2 + p6), and M = 18 (s2 + p6 + d10). See the elements in the text for more details.

4. The fourth shell or energy level is “N,” which may contain a maximum of 32 electrons; its orbital is called “f” subshell: for example, K = 2 (s2), L = 8 (s2, p6), M = 18 (s2, p6, d10), and N = 32 (s2 + p6 + d10 + f14). Refer to the elements in the text for more information.

5. The fifth shell or energy level is “O,” also with a possible maximum of 32 electrons; its highest orbital is also the “f” subshell: K = 2 (s2), L = 8 (s2, p6), M = 18 (s2, p6, d10, f14), and O = 32 (s2, p6, d10, f14).

6. The sixth shell or energy level is “P,” with a maximum of 10 electrons. Remember that the numbers of electrons in each shell (K, L, M, N, O, and P) for each individual element are added together to find the total number for a particular atom, which is also the element’s atomic number.

7. The seventh shell or energy level is “Q,” with a maximum of two electrons, and is repre- sented as Q = 2 (s2) with just two electrons in it first orbital. (This sequence holds until the element ununtrium-113, where Q = 3 (s2, p1), and those heavy elements beyond 113, where the “Q” shell may contain more than three electrons.)

Note: All elements with a depiction of higher energy levels or shells are both syntheti- cally produced and radioactive, and electrons are added to inner shells rather than the usual

Atomic Structure | 13 outer shell of the elements. As these heavy elements’ atomic numbers increase, their half-lives

decrease to a fraction of a second, and they are produced one or few atoms at a time. This concept is depicted with the data presented for each element.