What is a non polar formula?

Before determining if a compound is polar, you need to determine whether or not the bonds in that compound are polar. You also have to determine the molecular geometry of the bonds and any electron lone pairs.

Before talking about whether or not an entire compound is polar, take a look at what determines whether or not a bond is polar. You can then apply these rules to determine if each molecule is polar or nonpolar.

What Makes a Bond Polar?

A molecule is polar if one part of it has a partial positive charge, and the other part has a partial negative charge.

When in a bond, atoms can either share electrons (covalent) or give them up (ionic). The atom that holds the electrons closer will thus be more negatively charged than the other atom.

Electronegativity is a measure of how much a particular element wants electrons. In the Resources section you will find a periodic table which reports the electronegativity of each element. The higher this number, the more an atom of that element will "hog" the electrons in a bond. For example, fluorine is the most electronegative element.

Electronegativity values can help you determine what kind of bond exists between two atoms. Is the bond likely to be ionic or covalent? To do this, find the absolute value of the difference between the electronegativities of the two atoms. Based on this value, the following table tells you if the bond is a polar covalent bond, covalent bond or ionic bond.

Think about water. What is the electronegativity difference between atoms in water? The electronegativity difference between H (2.2) and O (3.44) is 1.24. As such, the bond is polar covalent.

Bond Polarity and Molecule Polarity

As you saw above, a bond within a molecule can be polar. What does this mean for the whole molecule?

When determining molecule polarity, all bonds must be considered. This means that the vector partial charge from each bond must be added up. If they a cancel out, then the molecule may not be polar. If there are vector components left, then the bond is polar.

In order to find the direction of these vectors, you have to examine the molecular geometry of the bonds. You can find this via valence shell electron-pair repulsion (VSEPR) theory.

The theory starts with the idea that electron pairs in the valence shell of an atom repel each other (since like charges repel). As a result, the electron pairs around an atom will orient themselves to minimize repulsive forces.

Take a look at water again. Water is bound to two hydrogens and also has two lone pair electrons. It has a tetrahedral bent shape.

To determine whether or not the molecule is polar, you have to look at the partial charge vectors on the two bonds in the molecule.

First, there are two electron pairs on the molecule, which means there will be a large negative partial charge vector in that direction.

Next, oxygen is more electronegative than hydrogen and will hog the electrons. This means that the partial charge vector on each bond will have a negative component pointing toward the oxygen.

The inward component of the vector on each bond will cancel. The portion pointing toward the oxygen will not cancel. As a result, there is a net partial negative charge toward the oxygen side of the molecule. There is also a net partial position toward the hydrogen side of the molecule.

This analysis reveals that water is a polar molecule.

What about CH4?

First, CH4 has no lone pairs since all the electrons are involved in a single bond between C and H. CH4 has a tetrahedral molecular geometry.

Next, the C-H bond is covalent as the difference in electronegativities is 0.35. All the bonds are covalent, and there will not be a big dipole moment. Thus, CH4 is a nonpolar molecule.

The difference between polar and nonpolar molecules can thus be found by the vectors of partial charge resulting from each bond.

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

Nonpolar Molecules

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

Our New Interactive Periodic Table

The best way to view properties & trends of the elements, including electronegativity, is with our new super-cool interactive periodic table. It has amazing colors, and you can view dozens of properties and see articles on all the elements!

Topics Covered in Other Articles

• Ionic vs Covalent bonds
• Molecule vs Compound
• Acid-Base Chemistry
• Polar-Covalent Bonds

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