Electron Configuration - How to write an electron configuration
By: Amanda C. & Hannah M.
(Figure 1) Diagonal Chart
(Figure 1) Diagonal Chart

Electron configuration is a form of notation which shows how the electrons are distributed among the various atomic orbital and energy levels. Electrons are able to move from one energy level to another by emission or absorption of a quantum of energy, in the form of a photon. Because of the Pauli exclusion principle, no more than two electrons may exist in a given atomic orbital; therefore an electron may only leap to another orbital if there is a vacancy there.

Niels Bohr: Prize-Winning Physicist
(Figure 2) Niels Bohr
(Figure 2) Niels Bohr

Niels Bohr was a Danish physicist who won the Nobel Peace Price for his contributions to physics. He was the first to suggest that the periodicity in the properties of the elements could be explained by the electronic structure of an atom. He based these predictions off of his current Bohr model of the atom. In his model, the electron shells were at a fixed distance from the nucleus. Each distance corresponds to a certain amount of energy that an electron can have. The farther an electron is from the nucleus, the higher the energy level it occupies. The difference between two energy levels is called a quantum of energy. In his model, an electron can only be in one level or another and not between energy levels.

Energy Levels and Sub-Shells
The highest number of energy levels possible is 7. There are four sub-shells, consisting of: s, p, d, f, in that order. “S” is the first sub-shell filled on each level, “p” is the second, and so on and so forth. The number of electrons possible to fill each sub-shell is different, and displayed in the chart below:

S orbital contains one orbital, can hold two electrons
P orbital contains three orbitals, can hold six electron
D orbital contains five orbitals, can hold ten electrons
F orbital contains seven orbitals, can hold fourteen electrons

Understanding the Notation
• The first number stands for the energy level of the atom.
• The letter “s” stands for the sub-shell
• The exponent of “2” tells how many electrons are in the energy level

Aid of the period table of elements
(Figure 3) Periodic Table of Elements (With Orbitals)
(Figure 3) Periodic Table of Elements (With Orbitals)

(Figure 3) The periodic table of elements is organized in a way that makes it easy to figure out the order of the orbital sets without memorizing them. The first two columns (alkali and alkaline metals) are the s orbital sets. The transition elements make up the d orbital sets. Columns III-VIII are the p orbital sets, and the rare-earth elements comprise the f orbital sets. The rows are also organized to make navigation easier.

Steps to writing an electron configuration
1. Use the periodic table of elements to find how many electrons an atom has. Do this by finding the atomic number of the atom (same as the number of protons).
2. Refer to the diagonal chart (Figure 1).
3. Start with the lowest orbital available, 1s, which holds a maximum of TWO electrons.
4. Fill in the orbitals, using the chart (Figure 1) to organize them in the correct order.
5. Check to see that each energy level is filled with the correct number of electrons. Add the numbers of electrons of each level and make sure it matches the total number of electrons.