Atomic+Orbitals

We all know that an atom is made up of electrons, protons and neutrons. In addition, we know that the neutrons and protons are what make up the nucleus which the electrons orbit. In chemistry, we want to be able to locate and characterize the electrons. To do this we must think about the electron in three dimensional space. Quantum numbers is a method that scientists use to describe the location of an electron. There are three quantum numbers, n, l ml, which represent each of the three dimensions. All quantum numbers are always integers.

- History: The term "orbital" was coined by Robert Mulliken in 1932. However, the idea that electrons might revolve around a compact nucleus with definite angular momentum was convincingly argued at least 19 years earlier by Niels Bohr, and the Japanese physicist Hantaro Nagaoka published an orbit-based hypothesis for electronic behavior as early as 1904. Explaining the behavior of these electron "orbits" was one of the driving forces behind the development of quantum mechanics.

"n" is the principle quantum number and can range from 1 to infinity. This value is the best estimate of the electrons distance from the nucleus. The value of "n" also defines the electron shell. Therefore, more than one electron can have the same "n" value. "l" is the angular momentum quantum number. As "n" was used to define the electron shell, "l" is used to define the electron subshells. "l" values can range from 0 to "n." In addition, each "l" value is assigned a label or name of the subshell which it represents. Below is a table of the first four subshells. The first three subshells are labeled according to the types of lines produced in the spectrum. After the fourth subshell, the labels procede in alphabetical order.


 * **Value of l** || **Corresponding Subshell Label** ||
 * 0 || s (sharp) ||
 * 1 || p (principal) ||
 * 2 || d (diffuse) ||
 * 3 || f (fundamental) ||
 * 4 || g ||

Last is the "ml" which is the magnetic quantum number. This number can range from negative to positive "l" including zero. "ml" represents the orbital within a subshell. The orbitals within a subshell are the same shape but different orientation. This brings up another point...the shapes of orbitals. Each orbital has a characteristic shape. The s, d, and p orbitals are shown below. Notice that the orbitals are not straight paths, but more like clouds. This shows us that electrons do not stay on one path around the nucleus. Instead, they move around the nucleus in a given region or "orbital." The probability of locating an electron is the greatest around the nucleus because that is where the attraction is strongest. The size of the orbital increases with the value of "n", the electron's distance from the nucleus. Also, observe the symetry in these orbitals.