What is a Polar Covalent Bond?

covalent bond example

Core Concepts

In this tutorial, we will be discussing what makes a bond polar, how a polar covalent bond is defined, examples of polar covalent bonds, and finally, steps to solve a polarity question.

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What determines the polarity of a bond?

The property of polarity consists of the distribution of charge throughout a molecule or compound. A molecule or bond is polar when it has a buildup of opposite charges on opposite ends; these charges come from the unequal sharing of electrons between atoms of the molecule. Conversely, a bond is considered non polar when its electrons are equally shared throughout a molecule, resulting in an even distribution of charges. Let’s take a look at an example of unequal sharing by examining a common example of a polar molecule, water:

polar covalent bond water example
In the diagram above, oxygen is more electronegative than hydrogen. Thus, it more strongly attracts the electrons shared in the bonds between itself and hydrogen, causing the oxygen side of the water molecule to be more negative. The oxygen-hydrogen bonds in the water molecule are polar.

Electronegativity is the property that determines to what extent a particular atom wants to share its electrons with neighboring atoms. Two atoms forming a bond with different electronegativities will share their electrons unequally, resulting in a polarized covalent bond. In the extreme case one atom will completely steal an electron from another, resulting in an ionic bond.

What is a polar bond?

Let’s discuss what is a polar bond. In a polar bond, two atoms share electrons unevenly. There is a bond between the atoms, and electrons are shared, but they are pulled more closely towards one of the atoms in the bond. The atom that pulls the electrons more closely has a slight negative charge, and the other atom has a slight positive charge in the opposite direction.

When is a bond considered a polar covalent bond?

What is a polar covalent bond?

A polar covalent bond occurs when atoms are shared unequally in a covalent bond. Specifically, when the difference in electronegativities of the two atoms in the bond is between 0.4 and 1.7. The terms polar bond and polar covalent bond are generally used interchangeably.

Polar Covalent Bond Examples

BondElectronegativity difference between atomsExample in a molecule
oxygen-hydrogen3.5 – 2.1 = 1.4water, H2O
carbon-chloride3.0 – 2.5 = 0.5carbon tetrachloride, CCl4
nitrogen-hydrogen3.0 – 2.1 = 0.9ammonia, NH3
sulfur-oxygen3.5 – 2.5 = 1.0sulfur dioxide, SO2
hydrogen-bromine2.8 – 2.1 = 0.7hydrogen bromide, HBr
*Note that even though the carbon-chloride bond is polar, CCl4 is not a polar molecule, due to its geometric structure. So, molecules can be nonpolar even if they have polar bonds.

For More Help, Watch Our Interactive Video on Explaining Polar Covalent Bonds!

Is XeF2 polar?

To solve this problem, we’ll take these steps:

  1. Determine the bonds in the molecule.
  2. Determine the atoms in these bonds and the electronegativity values of each of the atoms.
  3. Find the differences between electronegativity values of the atoms in each bond.
  4. Determine what types (polarity) of bonds.
  5. Draw the Lewis structure and the dipoles to determine the polarity of the molecule.

The only bond in the XeF2 molecule is the xenon-fluoride bond. The atoms in this bond are xenon (electronegativity 2.6) and fluoride (electronegativity 4.0). Thus, the electronegativity difference = 4.0 – 2.6 = 1.4.

Because 0.4 < 1.4 < 1.7, the xenon-fluoride bond is polar covalent.

This is the lewis structure of XeF2.

The two fluoride atoms have higher electronegativity values than xenon, meaning that they both pull electrons toward themselves. Because XeF2‘s molecular geometry is linear, the dipoles cancel out.

Therefore, the XeF2 molecule is nonpolar, even though its bonds are polar-covalent.

Polar Covalent Bonds – Further Reading