Oxygen Element

Oxygen Element Explained

oxygen mass number

The Oxygen element is an essential part of life on Earth and also serves as an excellent example in the process of metal corrosion which will aid our understanding of the operation of batteries.

Diatomic Oxygen gas (O2) makes up just under 21% of the atmosphere. All oxygen atoms contain 8 protons in their nucleus and have 8 electrons in their neutral state.

Isotopes of The Oxygen Element


Bohr diagram for Oxygen

The most common isotope is the 16-O, which consists of 8 protons and 8 neutrons.

Other isotopes have been synthesized for the oxygen element, ranging from 4 to 20 neutrons. However they are all radioactive and the most stable of these other forms, 15-Oxygen, has a half life of just 2 minutes meaning that these versions of Oxygen are never encountered in the ordinary world.


The Electron Structure of Oxygen

Outer shell electron structure for Oxygen element

Oxygen atoms have 8 protons and therefore 8 electrons in their neutral state. If we follow the subshell filling guide for elements, we end up with this: 1s2 2s2 2p4.

This tells us that Oxygen has two shells of electrons. The first is holds only two electrons and is completely filled. The second contains six electrons, with space for another two electrons to make the full complement of 8 which is necessary for stability. As these outer shell electrons are arranged in pairs, we get the electron dot diagram for Oxygen as shown to the left. We can see from this that Oxygen will want to either capture two electrons or share two electrons to achieve stability.

We can see a more detailed image of the electron structure of the Oxygen element below. Subshells are indicated by the black horizontal lines. The numbers in brackets show the maximum number of electrons that can be placed in that subshell is the number given in brackets.

subshell electron arrangement of Oxygen


The Behavior of Oxygen

The element Oxygen can either capture two electrons or share two electrons. We will cover the sharing first.

Sharing Two Electrons

In order to share electrons, an Oxygen atom needs to team up with another atom. To keep explanations simple, we will use only three different types of atoms to give examples of this sharing. We will use Hydrogen, Carbon and our Oxygen atom as described so far. The electron dot diagrams for these atoms are shown:

bonding practice with Oxygen, Carbon and Hydrogen

All we need to do now is match them up so that the single electrons make pairs. Remember that while Carbon and Oxygen both need 8 outer shell electrons, Hydrogen only needs two.

The following diagrams show the construction of various covalent compounds. The final stage of each shows the molecule with the electron pairs replaced with sticks.

This is the process for obtaining the structure of water, H2O:

constructing a water molecule from Oxygen and Hydrogen

Atoms can share between one and three electrons with another atom. Since Oxygen has two to share, it can form a double bond with another oxygen atom:

How to make an oxygen molecule

Finally we will do the same to produce Carbon Dioxide, CO2, (read more about how to reduce CO2 levels in the atmosphere):

building the Carbon Dioxide molecule using valence electrons

The possible combinations are endless.

Capturing Two Electrons

The other way Oxygen can obtain a full outer shell is by capturing two electrons from the environment around it. Since electrons are generally not found wandering freely, these electrons must be taken from other elements. This occurs when an oxygen atom, or a molecule of oxygen gas, encounters a metal .