electronic structure of atoms
Each electron in an atom is described by four different quantum numbers. Three of these quantum numbers (n, l, and m) represent the three dimensions to space in which an electron could be found. A wave function for an electron gives the probability of finding the electron at various points in space. A wave function for an electron in an atom is called an atomic orbital. The fourth quantum number (ms) refers to a certain magnetic quality called spin.n-the principal quantum number
The n quantam number relates to the size of the atomic orbital. n can have any positive integer value from 1 to 7. The smaller the n, the lower the energy, the higher the value of n, the higher the energy. In the case of any single-electron atom, or hydrogen atom, n is the only quantum number which determines the energy. The size of an orbital depends on n. The larger the orbital, the larger the value of n. Orbitals of the same quantum state belong to the same shell. To use an analogy for n, why not relate it to the size of a computer, where larger values would represent larger houses.
l-the angular momentum quantum number
l can have any integer value from 0 to 3. This quantum number distinguishes orbitals of a given n value which have different states. Or, the secondary quantum number gives the shape of the orbital so the analogy can be made to the shape of the computer with larger values associated with computers with more components.
m-magnetic quantum number
The third quantum number has to do with the orientation of an orbital in a magnetic field. Because of this, we can relate its values to different directions the computer might be facing.
The final quantum number is the spin quantum number, it describes the spin orientation of an electron.
The electron configuration of an atom is the particular distribution of electrons among available shells. It is described by a notation that lists the subshell symbols, one after another. Each symbol has a subscript on the right giving the number of electrons in that subshell. For example, a configuration of the lithium atom (atomic number 3) with two electrons in the 1s subshell and one electron in the 2s subshell is written 1s22s1.
| sublevel | orbital | maximum # of electrons |
| s | 1 | 2 |
| p | 3 | 6 |
| d | 5 | 10 |
| f | 7 | 14 |
The notation for electron configuration gives the number of electrons in each subshell. The number of electrons in an atom of an element is given by the atomic number of that element.
On the left we have a diagram to show how the orbitals of a subshell are occupied by electrons. On the right there is a diagram for the filling order of electrons in a subshell.
Here are some examples that show how to use the filling order diagram to complete the electron configuration for a certain substance.
| Element | # of Electrons in Element | Electron Configuration |
| He | 2 | 1s2 |
| Li | 3 | 1s22s1 |
| Be | 4 | 1s22s2 |
| O | 8 | 1s22s22p4 |
| Cl | 17 | 1s22s22p63s23p5 |
| K | 19 | 1s22s22p63s23p64s1 |
Often times you will be asked to find the electron configuration for something that looks like this:
53I
The 53 denotes the number of electrons in an atom of iodine. You would now proceed to do the electron configuration by looking at the filling order chart.
1s22s22p63s23p64s2
3d104p65s24d105p5