Bond Length & Angle in Chemical Compounds

Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

In this lesson, we will learn about the structure of chemical compounds and chemical bonds. We will learn about the bond length and angle of chemical bonds.

Chemical Structures

Water is something that we typically think of as a daily part of life, but it is also a chemical. The structure of water (and all chemicals) will play a big part in how it will react with other chemicals, and in the stability of those reactions. For example, water is simply hydrogen and oxygen bonded together. Other compounds similar to water (such as other compounds of similar molecule size as water) are in a gaseous state at room temperature.

Yet water is a liquid at room temperature. Also, when many compounds freeze, the frozen state will sink under the liquid state. But with water, the frozen ice floats on top of the liquid water. These amazing properties of water are all due to the unique chemical structure of water.

The unique structure of water allows the frozen ice to float on top of the liquid water.
ice floats

So the atoms that make up a chemical or molecule are not the only things that are important; the chemical structure is also important. Chemical structure is the way that atoms are bonded together to form the molecule. Molecules are made up of several atoms bonded together. A chemical bond is what binds two atoms together. Two important aspects of this chemical bond are the bond length and the bond angle.

Bond Length

Bond length is the distance between the nuclei (the center) of two atoms. Generally speaking, the longer the bond length, the easier it is to break apart those two molecules. We say 'generally' because there are other things to take into consideration than just the length of the bond.

For example, if we have a carbon and a nitrogen connected with a single bond, the average bond length is 147 pm (picometers), and the energy it takes to break that bond is 308 kJ/mol. If we have a single bond between two carbons, the average bond length is 154 pm, and the energy it takes to break that bond is 348 kJ/mol. The carbon-carbon bond is longer, but it takes more energy to break it because the carbon-carbon bond is stronger than the carbon-nitrogen bond.

This becomes more apparent when we look at an example with the same atoms connected together. Let's look at a carbon-carbon single bond, double bond, and triple bond:

  • Single bond: length is 154 pm and energy to break is 348 kJ/mol
  • Double bond: length is 134 pm and energy to break is 614 kJ/mol
  • Triple bond: length is 120 pm and energy to break is 839 kJ/mol

You can see that the shorter the bond length, the more energy it takes to break that bond.

There are many things that can affect the bond length. For example, the size of the atoms. The bigger the atoms, the bigger the bond length will be. Imagine you have a string attached to the inner center of two balls. Let's imagine both of these balls are basketballs, and let's imagine another set where both balls are golf balls. Even if the length of the string outside of the two balls is the same, the entire length of the string will need to be longer for the basketballs because it needs to go all the way into the middle of the basketball. In the same way, the bigger the atom is, the longer the bond length is.

Other things that affect bond length are: hybridization (more s-character means shorter bond length), the number of bonds (more bonds means shorter bond length), and the type of bond (polar bonds are shorter than non-polar bonds).

Hybridization is a theory that explains chemical bonds by explaining where the electrons are in a bond. The number of bonds includes single, double, and triple bonds. The types of bonds are polar, ionic, and covalent.

Bond Angle

Bond angle is the angle between two bonds that are connected to the same atom. A molecule with only two atoms doesn't have a bond angle; there needs to be at least three atoms before we start to see bond angles.

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