Molecular Polarity (Simplified) - Online Tutor, Practice Problems & Exam Prep

Molecular Polarity (Simplified) Concept 1

Recall that the polarity of chemical bonds arises from the unequal sharing of electrons between atoms based on electronegativity. We're going to say here that when we mention molecular polarity, we are talking about polarity that arises from an entire covalent molecule. With this idea, we have nonpolar versus polar molecules. Nonpolar molecules are any hydrocarbon, so compounds composed of only carbons and hydrogens, and any non-hydrocarbon with a perfect shape. Now, a compound has a perfect shape when the central element has 0 lone pairs and the same surrounding elements. If you break either one of those, then you are classified as a polar molecule. So that's any Lewis dot structure that doesn't have a perfect shape. Looking at the examples here, where there are 2 to 4 electron groups, in the first column, all of these shapes have 0 lone pairs on the central element, and it's assumed that all the surrounding elements would be the same. In these situations, all these molecules would be nonpolar. Once we start encountering cases where the central element has 1 lone pair, 2 lone pairs, etc., then all of these are classified as polar molecules. They no longer have perfect shapes. So, to be a perfect shape, your central element has to have 0 lone pairs, and the surrounding elements must be the same.

Molecular Polarity (Simplified) Example 1

Determine if carbon tetrachloride CCl₄ is polar or nonpolar. Alright. So we have carbon which is in group 4A, and chlorine which is in group 7A, and there are 4 of them, giving us 32 valence electrons total. Carbon will go in the center. It will form single bonds with the chlorines. Remember the surrounding elements have to follow the octet rule, so we put enough electrons around them to do that. And that takes care of our 32 valence electrons. Now we're going to say here that we have a molecule basically that we've drawn that has 4 bonding groups. Remember, bonding groups are just your surrounding elements, and it has 0 lone pairs. Here, our central element has no lone pairs, and we have the same surrounding elements. So this is a perfect shape. Since it's a perfect shape, that means the molecule will be nonpolar.

Determine if the compound of BCl₂F is polar or nonpolar.

• A. polar
• B. nonpolar

Determine if phosphorus trihydride, PH₃, is polar or nonpolar.

• A. polar
• B. nonpolar

Determine if difluorine selenide, F₂Se, is polar or nonpolar.

• A. polar
• B. nonpolar

Determine if carbon dioxide, CO₂, is polar or nonpolar.

• A. polar
• B. nonpolar

Here’s what students ask on this topic:

What determines the polarity of a molecule?

The polarity of a molecule is determined by the distribution of electron density across the molecule. This is influenced by the electronegativity of the atoms involved and the geometry of the molecule. If the central atom has no lone pairs and is surrounded by identical atoms, the molecule is typically nonpolar. However, if the central atom has lone pairs or is surrounded by different atoms, the molecule is likely polar due to an uneven distribution of electron density.

How do lone pairs on the central atom affect molecular polarity?

Lone pairs on the central atom affect molecular polarity by creating regions of negative charge that disrupt the symmetry of the molecule. This asymmetry leads to an uneven distribution of electron density, making the molecule polar. For example, in water (H₂O), the lone pairs on the oxygen atom create a bent shape, resulting in a polar molecule.

Why are hydrocarbons considered nonpolar molecules?

Hydrocarbons are considered nonpolar molecules because they consist solely of carbon and hydrogen atoms, which have similar electronegativities. This results in an even distribution of electron density. Additionally, hydrocarbons typically have symmetrical shapes, further contributing to their nonpolarity. Examples include methane (CH₄) and ethane (C₂H₆).

What is the significance of molecular polarity in chemical reactions?

Molecular polarity is significant in chemical reactions because it affects how molecules interact with each other. Polar molecules tend to dissolve well in polar solvents (like water), while nonpolar molecules dissolve in nonpolar solvents (like oil). Polarity also influences the strength and type of intermolecular forces, such as hydrogen bonding, which can affect reaction rates, solubility, and the physical properties of substances.

How can you predict if a molecule is polar or nonpolar?

To predict if a molecule is polar or nonpolar, follow these steps: 1) Draw the Lewis structure of the molecule. 2) Determine the shape of the molecule using VSEPR theory. 3) Check the electronegativity of the atoms involved. 4) Assess the symmetry of the molecule. If the central atom has no lone pairs and is surrounded by identical atoms, the molecule is likely nonpolar. If there are lone pairs or different surrounding atoms, the molecule is likely polar.