Is O2 an ionic or a covalent molecule?

The molecular formula for oxygen is O2, and it is a well-known diatomic molecule that is responsible for the existence of flora and fauna on the planet. The nascent oxygen (O), as we know, is a highly unstable atom that resides in a double atom form.

Because plants emit oxygen and humans and animals consume it, the balance of oxygen is maintained. Furthermore, oxygen is a key component of the earth’s many atmospheric cycles.

Furthermore, we know that O2 is the primary component of the ozone layer, which is found in the stratosphere and protects the earth from damaging solar radiation.

hν + O2  —> 2O

O2 + O.  —> O3

O3 + O. —> 2O2

O3  +  hν  —-> O2 + O.

hν = solar radiation photolyzing oxygen molecule

Oxygen is a colourless, odourless, and tasteless gas that is typically purified through fractional distillation of liquid air. Furthermore, oxygen in liquid and solid form has a faint blue colour that turns to orange, black, or red at low temperatures and high pressures.

Furthermore, while being a powerful oxidant, the oxygen molecule never catches fire and is not flammable. We must investigate its molecular structure and bonding behaviour because it is such a significant molecule. Let us now respond to the question:

So, is O2 an ionic or a covalent molecule? Because each oxygen atom requires two valence electrons to complete its octet, O2 is a covalent molecule. Each oxygen atom shares two electrons with the other oxygen atom to meet this demand, generating a strong oxygen-oxygen double shared covalent bond.

What are the differences between ionic and covalent bonds?

When one atom donates its valence electrons to another, ionic connections are established. Covalent bonds, on the other hand, are generated when valence electrons are shared across atoms to complete the octet and achieve a stable state.

It’s vital to remember that in a molecule with two identical atoms, only a common covalent link is produced.

The directed covalent bond exists in all three phases of matter: solid, liquid, and gas. As a result, molecules with covalent bonds exhibit hybridization, molecular orbital diagram, and polarity features.

Ionic bonds, on the other hand, are non-directional, hence the features demonstrated by covalent molecules are invalid. This is one of the main reasons why ionic bonding is only useful in the solid state.

Furthermore, it is assumed that molecules with ionic bonds have a high melting point, whereas molecules with covalent connections have a low melting point, based on this observation.

What is the significance of oxygen being a covalent molecule?

The Lewis structure of oxygen holds the answer to this question. To sketch it, we must first understand its electronic configuration. Because oxygen has an atomic number of 8, its electronic configuration is 1s2 2s2 2p4.

One oxygen atom requires two valence electrons in total, as the p shell requires six valence electrons to complete its shell.

It’s vital to remember that the fewer the valence electrons required, the greater the tendency to accept them, and vice versa.

As a result, each oxygen atom will try to take valence electrons, resulting in two oxygen atoms sharing valence electrons to complete their octet.

It’s obvious from the Lewis structure that oxygen atoms are joined together by a common covalent connection.

Furthermore, the double connection formed between two oxygen atoms consists of one sigma bond and one pi bond, ensuring the oxygen molecule’s stability.

It’s important to remember that the oxygen molecule has a low melting point, which has no bearing on the sigma covalent bond but does effect the pi covalent bond.

Is the covalent link between the oxygen molecules polar or nonpolar?

There is a discrepancy in electronegativity levels in polar covalent bonds. This difference produces an overall net dipole moment on the molecule, resulting in the separation of electric charges into two distinct positively and negatively charged ends.

Nonpolar molecules, on the other hand, are exactly the opposite, with no difference in electronegativity values, resulting in a net dipole moment of zero.

In comparison to polar molecules, no separation of electric charges occurs, and there is the least force of attraction between the atoms.

The oxygen molecule is nonpolar in nature, according to the aforementioned description, because both molecules within the atom are the same. This signifies the molecule is nonpolar because there is no variation in electronegativity values.

What influences covalent bonds?

When the valence electrons are shared between the atoms in order to create a molecule, a covalent bond is produced. The development of the covalent bond between the atoms is influenced by a number of factors.

Electron affinity, atomic size, ionisation energy, and electronegativity are examples.

  1. Electron affinity refers to the energy shift that occurs when an atom obtains a valence electron. The higher the electron affinity, the greater the atom’s willingness to take electrons.

Because it accepts the valence electrons and decreases the other atom, oxygen is a powerful oxidising agent.

  1. Ionization energy is another feature that contributes to the formation of a covalent connection between oxygen atoms. The least amount of energy required to excite the most accessible valence electrons in order to commence bond formation is determined by this attribute.

Both participating atoms must have a high ionisation energy, as in the case of the oxygen atom, in order to form a strong covalent connection.

  1. In line with this, atomic size is another factor that aids in the creation of strong covalent bonds. When it comes to creating covalent bonds between two atoms, the covalent radius is used to determine how far apart the participating valence electrons of both atoms are.

Each atom’s covalent radius will be half of the distance between the two nuclei in the case of generating a covalent radius. Because an equal amount of valence electrons participate and are present at an equal distance from one another, as well as a force of attraction on the other atom, this is the case.

As a result, the smaller an atom is, the less reactive it is and the closer it is to the positively charged nucleus.

As a result, valence electrons find it difficult to bind with other electrons in a shared format, such as a covalent bond.

  1. Finally, electronegativity refers to an atom’s ability to draw a shared pair of valence electrons towards itself.

It is self-evident that electronegativity is proportional to atomic size by definition. The electronegativity of the involved atoms must be high but the difference must be small in order to establish a covalent connection, making the molecule nonpolar.

Is there a covalent link between all diatomic molecules?

The diatomic molecules will be covalently linked and can be homonuclear or heteronuclear. In the case of homonuclear molecules, the valence electrons will be equally shared, resulting in a nonpolar covalent bond with zero electronegativity difference.

In the case of heteronuclear molecules, there will be a difference in electronegativity, resulting in the formation of a polar covalent bond.

Some people may believe that sodium chloride (NaCl) is not covalently linked because it is a diatomic molecule. It’s crucial to understand that ionisation causes sodium chloride to form.

Ionic bonds do not form in diatomic molecules because the crystal lattice is made up of a web of ions. In the case of sodium chloride, each ion is surrounded by six additional ions that are charged in the opposite direction, forming a crystal lattice.


The oxygen molecule is covalently bound, meaning both atoms share an equal number of valence electrons. The Lewis structure, which states that a double covalent link exists between the oxygen atoms, can be used to study it thoroughly. This double bond’s sigma bond is responsible for the molecule’s robust and stable structure.

The weak or incongruent behaviour, on the other hand, is primarily attributable to the pi bond’s bonding. Due to the fact that a single oxygen atom requires two valence electrons to complete its octet, the atom prefers to donate rather than accept.

This is why the participating two oxygen atoms share their valence electrons in order to generate one oxygen molecule.

Read more: Hybridization, Molecular Geometry, and the Lewis Structure of NH4+

Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.


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