Polar and Non-Polar Molecules

Molecules can be grouped as polar or non-polar molecules. Some are also in between.

The arrangement or geometry of the atoms in some molecules is such that one end of the molecule has a positive electrical charge and the other side has a negative charge. If this is the case, the molecule is called a polar molecule, meaning that it has electrical poles. Otherwise, it is called a non-polar molecule.

Whether molecules are polar or non-polar determines if they will mix to form a solution or that they don't mix well together. Also, polar molecules are water soluble, while non-polar molecules are fat soluble.

Questions you may have include:

• What is a polar molecule?
• What is an example of a non-polar molecule?
• What rule is there to determine if substances will form solutions?

This lesson will answer those questions.

Polar molecules

Chemical bonding is the result of either an atom sharing one or more outer orbit electrons with another atom or an atom taking outer orbit electrons from the atom with which it is bonding. Normally, an atom has an even distribution of electrons in the orbits or shells, but if more end up on one side that the other in a molecule, there can be a resulting electrical field in that area.

Water is polar

Water is a polar molecule because of the way the atoms bind in the molecule such that there are excess electrons on the Oxygen side and a lack or excess of positive charges on the Hydrogen side of the molecule.

Water is a polar molecule with positive charges
on one side and negative on the other

Examples of polar molecules

Examples of polar molecules of materials that are gases under standard conditions are:

• Ammonia (NH₃)
• Sulfur Dioxide (SO₂)
• Hydrogen Sulfide (H₂S).

Also, Ethanol is polar, since its oxygen molecule draws electrons towards it due to its high electro-negativity, causing a negative charge around itself.

Non-polar molecules

A non-polar molecule is one that the electrons are distributed more symmetrically and thus does not have an abundance of charges at the opposite sides. The charges all cancel out each other.

The electrical charges in non-polar Carbon Dioxide are evenly distributed

Examples of non-polar liquids

Most hydrocarbon liquids are non-polar molecules. Examples include:

• Toluene
• Gasoline

Alkynes are non-polar because they cannot be dissolved in water, as do polar molecules. However, alkynes but do dissolve in other non-polar substances. A rule is that like substances dissolve in like substances.

Examples of non-polar gases

Common examples of non-polar gases are the noble or inert gases, including:

• Helium (He)
• Neon (Ne)
• Krypton (Kr)
• Xenon (Xe)

Other non-polar gases include:

• Hydrogen (H₂)
• Nitrogen (N₂)
• Oxygen (O₂)
• Carbon Dioxide (CO₂)
• Methane (CH₄)
• Ethylene (C₂H₄)

Since Chloroform is more soluble in fats than in water, it is also classified as non-polar.