In this chemistry tutorial, we explain the difference between polar bonds and non-polar bonds. We then tell you the definition of a polar molecule, and what a non-polar molecule is. Last, but not least, you learn what a dipole moment is.
What do polar and non-polar mean?
In simple terms, polar means oppositely charged, and non-polar means equally charged. Covalent bonds can be polar or non-polar. To understand the difference between polar and non-polar bonds, it is essential to comprehend electronegativity.
What is electronegativity?
Electronegativity is the measurement of how much an atom wants to bond to another atom. Electronegativity increases from left to right and down each column on the periodic table. The Pauling scale describes the electronegativity of an element, with a scale from 0.7 to 4. Fluorine is the most electronegative element, with an electronegativity of 4. Cesium is the least electronegative element with an electronegativity of 0.7.
What makes a bond polar?
A polar bond is a type of covalent bond. A bond between two or more atoms is polar if the atoms have significantly different electronegativities (>0.4). Polar bonds do not share electrons equally, meaning the negative charge from the electrons is not evenly distributed in the molecule. This causes a dipole moment. A dipole moment occurs when one end of the bond is positive, and the other end is negative. A classic example of a polar bond is the bond in water between hydrogen and oxygen. The bond is classified as a polar bond because it has a large electronegativity difference of 1.4. The electrons in hydrogen are more attracted to the electrons in oxygen because oxygen is more electronegative.
What makes a bond non-polar?
Non-polar bonds are also a type of covalent bond. Unlike polar bonds, non-polar bonds share electrons equally. A bond between two atoms or more atoms is non-polar if the atoms have the same electronegativity or a difference in electronegativities that is less than 0.4. An example of a non-polar bond is the bond in chlorine. Chlorine contains two chlorine atoms. The electrons are shared equally because the electronegativity difference between the two atoms is zero.
What are Polar Molecules?
In chemistry, the definition of a polar molecule, is a molecule that has a charge on one side of the molecule, that is not cancelled out. It has a region of partial charge. One end is slightly positive one end is slightly negative. They are generally asymmetrical, with an uneven distribution of the electrons.
Polar molecules can have ionic or polar covalent bonds. A molecule with two poles is called a dipole. When you measure the amount of polarity of a molecule, the result is called the dipole moment.
If a molecule is non-polar, then the molecules either share the electrons evenly, e.g. they have a non-polar bond, or the polar bonds are symmetric, in the cases of carbon dioxide or carbon tetrachloride. In those molecules, there are dipoles but they cancel out due to the symmetry.
Polar molecules tend to stick together and line up in groups, which affects the properties of polar compounds like water. Water molecules can actually align themselves in the presence of an electrostatic force. Also, polar solvents tend to dissolve polar solutes, and non-polar solvents dissolve non-polar solutes.
Examples of Polar Molecules
Is HF polar?
Yes, hydrofluoric acid HF is polar because of the large electronegativity difference between hydrogen and fluorine. The molecule is polar covalent.
Is water a polar molecule?
Yes, because of the bent non-symmetrical shape of the molecule. More of the electrons are attracted to the oxygen atoms, resulting in a net charge.
Is acetone polar or nonpolar?
Because of the carbonyl group, acetone is a somewhat polar molecule. There are different degrees of polarity, and acetone is less polar than water, because only part of the acetone molecule has a polar bond.
More examples of polar molecules
Sulfur dioxide SO2, ammonia NH3, carbon monoxide CO, ethanol C2H5OH, methanol CH3OH, hydrogen sulfide H2S, chloromethane CH3Cl, ozone O3, phosphorus trichloride (because it has trigonal pyramidal geometry) PCl3
In a nonpolar molecule, there are no positive or negative poles formed in the molecule. Any charges are distributed evenly across the molecule. Nonpolar molecules are generally symmetrical, like the tetrahedral molecule carbon tetrachloride. Another example is boron trifluoride, which is trigonal planar. In symmetrical molecules, the dipole charges cancel out.
Nonpolar molecules usually will dissolve well in nonpolar solvents, but tend to be insoluble in water.
Examples of Non-polar Molecules
Is Carbon Dioxide polar?
No, CO2 is not polar, even though the bonds are polar. Because of the linear symmetry of the molecule, the negative charges around the oxygen atoms cancel out.
Is HCl polar or nonpolar?
Because chlorine is more electronegative than hydrogen, hydrochloric acid HCl forms a polar bond, and is therefore a polar molecule. There is no symmetry which could cancel out the dipole charge.
More examples of non-polar molecules
Benzene C6H6, Methane CH4, Carbon Tetrachloride CCl4, boron trifluoride (because it is has trigonal planar geometry) BF3, hexane C6H14, nitrogen N2
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Topics Covered in Other Articles
Cool Chemistry Video that is NOT about Polar Bonds
- Iodine is a common additive to drugs because of its non-polar property.