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Polar And Nonpolar Covalent Bonds

When two atoms combine, just like in the formation of a hydrogen molecule, the atoms are one and the same and they have the same electronegativity. But, if the two atoms that are combined via covalent bond are different, then there is unequal sharing of electrons due to the electronegativity difference between those atoms. Such a bond is called a polar covalent bond. The former case (H2 molecule) is an example of a nonpolar covalent compound. In the HBr molecule, the bonding electrons will be more attracted to the more electronegative of the two atoms, namely bromine. So the bonding electrons are likely to spend more time closer to the more electronegative atom or group. Hence, this bond is polar.


The delta+ (δ+ ) indicates the partial positive charge of the hydrogen atom, and delta (δ) indicates the partial negative charge of the bromine atom. Small and equal charges being separated by a small distance constitute a dipole. The polarity is quantitatively represented in terms of dipole moment, which is the charge times the distance between the charges. Now that you know dipole moment, let's learn how to represent this.

image\Ch 5 page 65 last graphic.png

Here the net dipole moment is as indicated by the arrow.

When there are more than two dipoles, the net effect is the vector sum of all individual dipoles in the molecule. For example, in carbon dioxide (CO2) the net dipole moment is as shown below.

image\24522 Ch 5.jpg

Since the dipoles are equal and opposite, the vectors of the dipoles cancel out.

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