Electron Configuration and Structure


Electrons exist in shells around the nucleus and have different configurations and layouts based on the element in the periodic table. Electrons are also very important in bonding.

The electrons are some of the most important subatomic particles when it comes to the atom. The electron is responsible for the bonding and reactivity of an atom. The electrons are negatively charged particles with a mass of 1/1836 that of a proton or neutron. They are much smaller than the nucleus but play a huge role.

An electron configuration is the layout of the electrons in the shells around the nucleus. Electrons exist in shells around the nucleus and orbit in different shapes. The key way to understand the basics of the electrons is the number of shells and the number of electrons they can hold. The first shell can hold 2 electrons, the second shell can hold 8 electrons and the 3rd shell can hold 18. This plays a very important role in the structure of the periodic table and some of the trends and patterns of reactivity.


If drawing the electron diagram the electrons can be shown in the shells much like the diagram below. However, when writing the electron configuration it is represented as numbers with commas separating the shells. The diagram below has 2, 8, 8, 1 this means there are 2 electrons in the first shell, 8 in the second, 8 in the third and then 1 in the fourth.

Two simple rules to remember are that the Group number (column) the element is in is the number of electrons in the outer shell. The Period (rows) the element is in relates to the number of shells the atoms have. One thing to note is that the transition metals do not always follow this it only works for groups 1,2 and then 13 to 18 as groups 3 to 12 are transition metals.

For example, Lithium is in Group 1 and so is Sodium. But if we compare their electron structure of the two atoms. It can be seen that Lithium and Sodium both have 1 electron in the outer shell, the only difference is that Sodium has one more shell of electrons. The configurations would be Li 2,1 and Na 2,8,1.


The same trend can be seen in Group 17, the Halogens. In Group 17 there are 7 electrons in the outer shell. Comparing Fluorine to Iodine, whilst Iodine is much larger and has 5 shells they both still have 7 electrons in their outer shells. The electron configurations would be F 2,7 and I  2,8,18,18,7

Terms in section

A neutron is a neutral sub atomic particle that makes up the nucleus with the proton


A proton is a positive particle that makes up the atom in the nucleus with a positive charge


The electron is the smallest sub atomic particle that make up the atom. Has a negative charge and is located in shells that orbit the nucleus

Sub atomic

Sub atomic is a term used to describe parts of the atom that are the smaller than the atom itself, the proton neutron and electron


The nucleus is the term given to the centre of the atom comprising of the proton and neutron


Groups are the columns of the periodic table where the elements are arranged vertically due to their similarities of properties.


Periods are the rows of the periodic table. As you go along periods the number of protons and neutrons increases and the number of electron shells remains the same.

Transition metals

Transition metals are the central section of the periodic table containing the majority of the metals. Also have d sub orbitals producing certain chemical properties

Electron configuration

The electron configuration is the numerical layout of electrons in the orbitals around the atom. Can be done simply for example lithium has 3 electrons and has 2 in the first shell (as this is the maximum) and 1 in the second shell giving it the configuration 2,1.


The shell is the path that electrons follow outside the nucleus. Shells can be considered as energy levels and the further away from the nucleus the higher in energy.


Can Elements Be Made in the Lab?


History of Chemistry: Alchemy