Polarity of CO2: Why Does Non-Polar CO2 Dissolve In Polar H2O?

The polarity of a molecule determines how the molecule will interact with other molecules in a chemical reaction. Molecules like CO2 have several applications, from biological to industrial. Perhaps the versatility of CO2 can be traced to its polarity.

Another striking thing about the polarity of CO2 is that it is a polar molecule yet is soluble in water. The nature of CO2 largely influences its physical and chemical properties.

However, to fully understand the polarity of CO2, you will need to first understand its molecular geometry – shape, bond angles, bond length, and the polarity of the individual bonds. These are some of what you will get to learn in this article. Keep reading.

About CO2

Carbon dioxide, CO2, is a covalent molecule with one carbon atom and two oxygen atoms. It is a tetravalent atom, that completes its valency by sharing covalent double bonds with the oxygen atoms. CO2 has a molar mass of 44 g/mol and a density of 1.977 g/mol.

It is a stable gas at room temperature. CO2 is a colorless gas with a mildly sharp odor. At high concentrations, the gas has a sharp and acidic smell. It is a non-flammable gas with a melting point of -68.08°F (-56.6°C) and a boiling point of -109.3°F (-78.5°C).

Carbon dioxide is a versatile gas with several applications across sectors and industries. It is the universal source of carbon to the carbon cycle and several life processes that occur on the Earth.

Through biological processes that require the addition and removal of this gas, CO2 is always present in the atmosphere and on the Earth. Photosynthesis and cellular respiration are two biological processes that use up and produce CO2 for the sustenance of life. 

By the influence of human and non-human activities, the original 281 parts per million (ppm) CO2 present in the atmosphere has increased to 421 ppm.

Additionally, CO2 is a key greenhouse gas and is responsible for global climate change. It creates the greenhouse effect in combination with methane, water vapor, and other gases.

What is the polarity of CO2?

CO2 is a non-polar molecule. The carbon and oxygen atoms are symmetrically arranged in a linear molecular geometry with a bond angle of 180°.

However, the polarity of CO2 seems to be strange because the C=O bonds are polar considering the electronegativities of the carbon and oxygen atoms. Carbon has an electronegativity of 2.55 and oxygen has an electronegativity of 3.44.

If you find the difference, you will see that there is an electronegativity difference of 0.89. According to the electronegativity guidelines for determining polarity, the bond between atoms is polar if the electronegativity difference is greater than 0.4 and non-polar if the difference is less than 0.4.

So, the deduction that the C=O bonds are polar is true. However, the two polar bonds cannot successfully make the overall molecule polar because of the symmetrical arrangement of the atoms in the molecule and the electron pair repulsion in the valence shell (according to the VSEPR theory).

If you consider the Lewis structure of CO2, you will see that the molecule has two sigma bonds and no lone pair of electrons. The bonding pair of electrons around the carbon atom repel each other and pull the oxygen atoms to the ends of the molecule, maintaining the linear shape.

CO2 would have been polar if it had a lone pair of electrons that could exert a greater repulsion on the bond and alter the shape to a bent structure.

Furthermore, the dipole moments on the two polar C=O bonds cancel out each other, resulting in a zero net dipole moment. There is no net shifting of electrons in any direction. As a result, there is no accumulation of charges on either the carbon or oxygen atom, which is typical of a non-polar molecule.

Is CO2 an ionic or covalent molecule?

CO2 is a covalent molecule. First, the constituent atoms are nonmetals that share electrons. In ionic compounds, the constituent elements are usually a metal and a nonmetal, and one loses electrons while the other gains electrons to form a bond.

Why does CO2 dissolve in water despite being non-polar?

The solubility of CO2 in water despite being a non-polar molecule is a result of its polar C=O bonds and the formation of the intermediate carbonic acid.

The polar C=O bond interacts with the polar bonds of the water molecule and forms carbonic acid. The presence of carbonic acid in the system increases the chances of CO2 dissolving in water.

This phenomenon is explained by Le Chatelier’s principle (or the equilibrium law) which states that a change in one of the variables (temperature or pressure) that describe a system at equilibrium produces a shift in the position of the equilibrium that counteracts the effect of this change.

The solubility of CO2 in water is dependent on temperature, pressure, and concentration.

The reaction is as follows:

CO2 (g) + H2O (l) ⇌ H2CO3 (aq)

The solubility of CO2 decreases with increasing temperature. The dissolution of CO2 in water is an exothermic process. An increase in the temperature of the system will cause a shift in the equilibrium to the left. As a result, carbonic acid will be converted back to carbon dioxide and water to reduce the temperature of the system.

Conversely, an increase in pressure in the system will favor the forward reaction. More carbonic acid will be formed to reduce the pressure. However, this can only occur when there is an increase in the concentration of CO2 in the system.

In essence, a system at equilibrium will always produce a shift in its position to counteract the effect of a change in variables – temperature, pressure, and concentration.

How does the polarity of CO2 affect its reactions?

The non-polar nature of CO2 affects its solubility in water, its behavior in chemical reactions, and its role as a greenhouse gas in the atmosphere.

The partial solubility of CO2 in water is due to the weak attraction between the non-polar CO2 and polar H2O. However, it favors the formation of carbonic acid which is a crucial compound in biological systems and the carbon cycle.

Also, as a non-polar gas, CO2 mixes well with other gases in the atmosphere. As a result, it diffuses well into the atmosphere and impacts the climate on the Earth. This can be both an advantage and a disadvantage.

For the advantage, sufficient levels of CO2 in the atmosphere improve the growth of green plants and strengthen food security. Plants become more drought-resistant as they learn how to use water well. Other benefits are better ventilation and the production of energy.

Some disadvantages of CO2 in the atmosphere are climate change, deforestation, ocean acidification, and air pollution.


Why is SO2 polar and CO2 is non-polar?

SO2 is polar and CO2 is non-polar because of their structures. SO2 has a bent structure, while CO2 is linear. In the linear structure of CO2, dipole moments cancel out each other. But dipole moments do not cancel out each other in the bent structure of SO2.

The above phenomenon is the explanation for the non-polar nature of CO2 and the polar nature of SO2.

Does CO have the same polarity as CO2?

CO and CO2 are both oxides of carbon and tend to look identical except for the extra oxygen atom in CO2. However, CO is polar while CO2 is non-polar. This is because of the electronegativity difference between carbon and oxygen.

But in the case of CO2, the dipole moments from the individual polar C=O bonds cancel each other and make the molecule non-polar.

What is the formal charge of CO2?

To get the overall formal charge of CO2, you need to determine the formal charge of the individual atoms in the molecule.

To determine formal charge (FC), subtract the number of bonding electrons and half the number of non-bonding electrons from the number of valence electrons. That is, FC = V – N – B/2.

Following this formula, the formal charge of C can be determined as follows:

C = 4 – 0 – 8/2

C = 0

The formal charge for each oxygen atom,

O = 6 – 4 – 4/2

O = 0

The overall formal charge,

CO2 = 0 + (0 x 2)

CO2 = 0.


CO2 is a non-polar molecule with polar C=O bonds. The overall non-polar nature is due to the annulment of the dipole moments on the two C=O bonds to generate a zero net dipole moment. The annulment of dipole moments is because of the symmetrical arrangement of the atoms.

Despite the non-polar nature of CO2, about 30% of it is soluble in water due to the polar C=O bonds. CO2 is indeed a unique molecule with various applications, which is directly or indirectly a result of its polarity – of bonds and the overall molecule.  

Also, learn about the polarity of a unique molecule BCl3 (boron trichloride).

Thanks for reading.