O2 is a chemical element within the 16th group of the periodic table, called chalcogens. Besides being one of the simplest elements existing on this planet, oxygen is of great importance on the Earth.
Due to this reason, it is essential to study its Lewis structure. The existence of a strong shared covalent double bond between the two oxygen molecules within a single O2 molecule makes it crucial to study the Lewis structure even more.
Significance of Lewis structure
Lewis structure is a diagrammatic representation of showing the bond formation between the atoms of molecules.
Furthermore, this structure also helps with determining the lone electrons existing within the molecule and how they will be acting in a bond formation.
This diagram shows bonds with the help of lines and lone pairs of electrons as dots.
The Lewis structure helps with understanding how electrons are distributed within a compound along with its molecular geometry.
Besides this, the lewis structure helps with determining the hybridization of the molecule.
Lewis structure of O2
The Lewis diagram of O2 shows two oxygen atoms having twelve dots, of valence electrons. Where six are arranged, around each oxygen atom in a way that one side has four valence electrons.
These four valence electrons form two shared pairs of covalent bonds, providing a stable structure to the oxygen molecule.
Some elements of the periodic table tend to bond in such a manner that each atom has to have eight electrons in the outermost shell or the valence shell.
It gives a similar electronic configuration as that of a noble gas. These eight electrons present in the outermost shell are drawn and counted during the lewis structure.
What are the Valence electrons?
The valence electrons are present in the outermost shell of an atom which participates in a bond formation.
This bond formation further leads to the formation of a molecule and eventually a compound.
The valence electrons either get accepted or donated to form a strong bond, usually which is covalent in most of the cases.
How many valence electrons/lone pair of electrons are in O2?
The analysis of the number of valence electrons present in one oxygen (O) molecule is done with the help of the electronic configuration.
The atomic number of one oxygen atom is eight where its electronic configuration shows a deficiency of 2 electrons in the 2p shell.
It concludes to the fact that oxygen needs two electrons to achieve a stable condition.
The octet rule says that the elements bond in such a manner that they tend to achieve a maximum of eight electrons in their outermost shell or the valence shell.
As we studied above that one oxygen atom has a deficiency of two valence electrons, it readily accepts two electrons.
So, a single oxygen molecule has six electrons in its octet. If we look for O2, then the number will be O2: 6+6 = 12. In total, an O2 molecule needs four valence electrons to complete its octet and achieve a stable condition.
The Geometrical Structure of O2
To study the geometrical structure of O2, it is important to look at the electronic structure of a single oxygen atom first.
The Lewis structure is formed considering the eight electrons comprising the octet rule. The one side of each oxygen atom is written, with a maximum of two electrons (so, two dots).
So, the deficiency of two valence electrons makes one oxygen atom have six valence electrons in its octet. The first diagram depicts a pictorial representation of six valence electrons in one oxygen atom.
O2 being a diatomic molecule forms a linear geometrical structure held by a double bond. The bond angle formed between both Oxygen atoms is 180 degrees.
Steps of drawing Lewis diagram
- Find total valence electrons: It is two for each oxygen atom
- Find how many electrons are needed: It is four for one O2 molecule
- Look for the total number of bonds forming: Double covalent bonds are forming in an O2 molecule
- Choose a central atom: Both the atoms will be central
- Draw the skeleton
Each dot in the diagram represents an electron, where it is interesting to see how electrons are shared between the two oxygen atoms to achieve the stable octet having 8 electrons.
From the second diagram, it can be concluded that each O2 molecule shares two pairs of valence electrons to achieve its octet of 8 electrons.
How two pairs of valence electrons are shared between O2?
When an atom is scarce of valence electrons, it readily either accepts or donates electrons to achieve a stable condition.
The lower the number of valence electrons needed, the tendency to donate the valence electrons increases.
As the oxygen atom requires only two valence electrons, it readily shares them with another oxygen atom which is also in need of two valence electrons.
The bond which is formed between a shared pair of electrons is a covalent bond.
As there is a stable balance between the attractive and repulsive forces due to the sharing of the electrons, the covalent bond formation is tough to break.
Moreover, as there is a formation of two covalent bonds between four valence electrons of the O2 atom, it becomes highly stable and is not easy to bond with the O2 atom without the presence of any catalyst.
Why there is a strong covalent bond in O2?
A single covalent bond is usually made up of a sigma (σ) bond which is the strongest covalent bond, due to head-on overlapping between the shared pair of valence electrons.
After σ, comes the Pi (π) bond, which is weaker than the σ bond, as they occur because of lateral overlapping between the shared pair of electrons.
As O2 has one σ and one π bond, because of which valence electrons in it undergoes both head-on and lateral overlapping.
Due to this reason, O2 is a stable molecule. The below-mentioned diagram is showing sigma and pi overlapping within the oxygen molecule.
Here, an oxygen molecule is formed due to the occurrence of overlapping between the two partially-filled p-orbits within each of the oxygen atoms (consult the electronic configuration of the O2 molecule here again).
The O2 molecule is sp2 hybridized because it is formed by inter-mixing of 1 s and then 2 p orbitals.
It leads to the movement of one of the electrons from the s orbital into one of the 2p orbitals.
This movement leads to the formation of three new hybrid orbitals that are equal in energy. The diagram showing this structure can be seen in the previous question.
The oxygen molecule lies under the umbrella of the diatomic molecule. Therefore it forms a linear geometrical structure and both oxygen atoms have equal electronegativity and other properties.
Therefore, both atoms share equal ratios of bonded shared electrons and the overall molecule turns out to be nonpolar in nature.
For more detail, you can go through an interesting article regarding O2 polarity.
Molecular Orbital (MO) Diagram of O2
The molecular orbital diagram shows the energy state at each level where the excited state increases from the bottom to the top.
The left-hand side diagram is of O2 at ground level whereas the right-hand side diagram is of rearranged electrons as per the Lewis structure within the O2 molecule.
It takes a lot of energy to pair up the electrons within the same orbital. So, the diagram having no unpaired electrons is at higher energy.
It means it is at a much higher excited state than the other.
The Lewis structure is a dot diagram to determine how many lone valence electrons are present and absent within an atom. Moreover, it is easy to figure out which bond has been formed between the atoms of a molecule, with the help of this diagram.
The O2 molecule forms a double covalent bond between two shared pairs of electrons. Furthermore, it is the covalent bond which leads to sp2 hybridization in the O2 molecule.