Polar Covalent Bond

A polar bond is a type of chemical bond. It can be said that it is the line between the formation of a pure chemical bond and an electrovalent bond. However, if we would like to define it more accurately, a polar chemical bond is a bond that exists between two atoms consisting of electrons that are unevenly distributed. Due to this state, the molecules tend to possess some electrical moment wherein the 2 ends are either slightly positive or negative.

Electronegativity plays a significant role in determining the different types of covalent bonds. Electronegativity is the tendency of an atom to draw in a shared pair of electrons towards itself. It has no units. The chemical bond formed between two atoms in molecules whose electronegative difference exists is understood as a polar chemical bond. Before discussing the polar covalent bond, let us understand the properties of covalent bonds. 

Properties of Covalent Bond

Some properties of covalent bonds are discussed below.

• Covalent bonds are very powerful chemical bonds that exist between atoms.

• Covalent bonds do not form new electrons. The bond only pairs electrons.

• Covalent bonds very rarely break spontaneously after being formed.

• Covalent bonds are directional where the atoms that are bonded showcase specific orientations relative to at least one another.

• Most compounds that have covalent bonds have relatively low melting points and boiling points.

• Compounds with covalent bonds usually have lower enthalpies of vaporization and fusion.

• Covalent compounds don’t conduct electricity due to the shortage of free electrons.

• Covalent compounds are not soluble in water.

Polar Covalent Bond- Explanation

Polar covalent bonds are formed between two nonmetal atoms that have different electronegativities. Let us consider A and B with an electronegativity difference that is not equal to zero having a chemical bond between them. The shared pair of electrons forming a bond between A and B move towards electronegative B.

Then B gets partial charge and attains ‘A’.  A gets partially charged, with two charges (Poles are formed and it's referred to as Dipolar molecular or dipole or polar covalent molecule) as in H – Cl. In this molecule, the shared pair of electrons move towards a high electronegative chlorine atom. Then the H-atom gets a partial positive charge, and the Cl atom gets a partial negative charge, hence a dipole is formed.

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What are the Properties of Polar Covalent Compounds?

• Physical State 

These compounds can exist as solids due to a greater force of interaction.

• Melting and Boiling Points 

They have greater melting and boiling points than non-polar compounds.

• Conductivity

They conduct electricity within the solution state due to the mobility of ions.

• Solubility

These are highly soluble in polar solvents like water.

Examples of Molecules with Polar Covalent Bonds

Water (H2O) is a molecule having a polar covalent bond. The electronegativity value for oxygen is 3.44, whereas the electronegativity value for hydrogen is 2.20. The difference in the distribution of electrons accounts for the best shape of the molecule. The oxygen "side" of the molecule features a net charge, while the 2 hydrogen atoms (on the opposite "side") have a net charge.

Hydrogen fluoride (HF) is another example of a molecule that features a polar chemical bond. Fluorine is the more electronegative atom, therefore the electrons within the bond are more closely related to the fluorine atom than with the hydrogen atom. A dipole forms with the fluorine side having a net charge and therefore the hydrogen side having a net charge. Hydrogen fluoride may be a linear molecule because there are only two atoms, so no other geometry is feasible.

The ammonia molecule (NH3) has polar covalent bonds between the nitrogen and hydrogen atoms. The dipole is such that the nitrogen atom is more negatively charged, with the three hydrogen atoms all on one side of the nitrogen atom with a positive charge.

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Which Elements Form Polar Covalent Bonds?

Polar covalent bonds form between two non-metal atoms that have a sufficient electronegativity difference. The electronegativity values are marginally different, the bonding electron pair is not equally shared between the atoms. For example, polar covalent bonds are normally formed between hydrogen and any other non-metal. The difference in electronegativity values between metals and non-metals is very large, therefore, they form ionic bonds with each other.