The orbital letters are associated with the angular momentum quantum number, which is assigned an integer value from 0 to 3. The s correlates to 0, p to 1, d to 2, and f to 3. The angular momentum quantum number can be used to give the shapes of the electronic orbitals.
What Does S, P, D, F Stand For?
The orbital names s, p, d, and f stand for names given to groups of lines originally noted in the spectra of the alkali metals. These line groups are called sharp, principal, diffuse, and fundamental.
Shapes of Orbitals and Electron Density Patterns
The s orbitals are spherical, while p orbitals are polar and oriented in particular directions (x, y, and z). It may be simpler to think of these two letters in terms of orbital shapes (d and f aren't described as readily). However, if you look at a cross-section of an orbital, it isn't uniform. For the s orbital, for example, there are shells of higher and lower electron density. The density near the nucleus is very low. It's not zero, however, so there is a small chance of finding an electron within the atomic nucleus.
What the Orbital Shape Means
The electron configuration of an atom denotes the distribution of electrons among available shells. At any point in time, an electron can be anywhere, but it's probably contained somewhere in the volume described by the orbital shape. Electrons can only move between orbitals by absorbing or emitting a packet or quantum of energy.
The standard notation lists the subshell symbols, one after another. The number of electrons contained in each subshell is stated explicitly. For example, the electron configuration of beryllium, with an atomic (and electron) number of 4, is 1s22s2 or He2s2. The superscript is the number of electrons in the level. For beryllium, there are two electrons in the 1s orbital and 2 electrons in the 2s orbital.
The number in front of the energy level indicates relative energy. For example, 1s is lower energy than 2s, which in turn is lower energy than 2p. The number in front of the energy level also indicates its distance from the nucleus. The 1s is closer to the atomic nucleus than 2s.
Electron Filling Pattern
Electrons fill up energy levels in a predictable manner. The electron filling pattern is:
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f
- s can hold 2 electrons
- p can hold 6 electrons
- d can hold 10 electrons
- f can hold 14 electrons
Note that individual orbitals hold a maximum of two electrons. There can be two electrons within an s-orbital, p-orbital, or d-orbital. There are more orbitals within f than d, and so on.