Boxes, or horizontal lines represent the orbitals, arrows represent the electrons, and if an orbital is full, the electrons must be of opposite spin–one arrow pointing up and the other one pointing down. An orbital box diagram can be written as well. The electron configuration for carbon is 1s 22s 22p 2.

Reading the periodic table from left to right, the boron atom has 5 electrons, and the electron configuration is 1s 22s 22p 1. The four electrons of Be go into the 1s and the 2s orbitals giving the electron configuration of 1s 22s 2. Next we go to lithium with 3 electrons two of the electrons go into the 1s orbital and the third electron into the 2s orbital giving an electron configuration of 1s 22s 1. Helium has 2 electrons and both electrons go into the 1s orbital and the electron configuration is 1s 2. Hydrogen has 1 electron which goes into the 1s subshell. You only need to know where the blocks are located on the periodic table. When reading the periodic table from left to right, one can easily write an electron configuration without memorizing the filling order. The periodic table below, shows the s, p, d, and f-blocks. The filling order follows:ġs→2s→2p→3s→3p→4s→3d→4p→5s→4d→5p→6s→4f→5d→6p→7s→5f→6d→7pĮlectron configurations and orbital box diagrams can be written right from the periodic table. For example the 1s orbital is filled and then we can fill the 2s orbital and go on to the 2p orbitals. The lowest energy orbitals must be filled first. In other words, the orbitals in a subshell must be half filled before pairing electrons. Hund’s Rule specifies that when orbitals of equal energy are available, the lowest energy electron configuration has the maximum number of unpaired electrons with parallel spins. The Pauli Exclusion Principle states that each orbital may contain a maximum of 2 electrons electrons must have opposite spins.ģ.

The Aufbau Principle states that electrons are always placed in the lowest energy sublevel that is available.Ģ.

Diagram carbon electron configuration