Tutorials

Bond Order vs. Bond Length

Core Concepts – Bond Length

In this tutorial, you will learn about the definition of a chemical bond, and the key differences between bond order and bond length. You will also learn about how these characteristics relate to each other, to then be able to apply them to a chemical structure.

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Vocabulary

Covalent Bond: An atomic linkage through the sharing of electrons between 2 atoms (typically non-metals).

Molecule: A compound formed through the bonding of 2 or more atoms.

What is a Bond?

A chemical bond is a force between molecules or atoms, that allows for the formation of chemical compounds. Bonds arise from the attractive forces that are present in between atoms.

What is Bond order?

Bond order is the number of covalent bonds existing between a pair of atoms. It is also used to determine the stability of a bond, as a higher bond order indicates a more stable bond. This is due to an increased attraction between electrons, making the atoms in the molecule being held more tightly together.

Steps on determining bond order:

Bond order between 2 atoms:

  1. Draw a Lewis structure for a given molecule
  2. Count the number of bonds between the two atoms (Single bond=1, Double bond=2, Triple bond=3)
  3. Since there is only one bond group between 2 atoms, the bond order is the same as the total number of bonds.

Example:

\chemname{\chemfig{H-[:0]O^\ominus}}{hydroxide}

Since there is a single bond between the hydrogen and oxygen atoms in hydroxide, the total bond order is 1.

Bond order for a Polyatomic molecule:

  1. Draw a Lewis structure for a given molecule
  2. Count the total number of bonds between all bonding groups (Single bond=1, Double bond=2, Triple bond=3)
  3. Divide the total number of bonds by the number of bonding groups.

Example:

\chemname{\chemfig{^\ominus O-[:30]N(-[:20,0.25,,,draw=none]^\oplus)(=[:90]O)(-[:-30]O^\ominus)}}{nitrate}

Since there are a total of 4 bonds between the oxygen atoms and nitrogen in nitrate, with 3 bonding groups present, the total bond order is 4/3.

What is Bond length?

Bond length describes the distance between the nuclei of bonded atoms. The length of a bond is inversely proportional to the bond order; the higher the bond order, the shorter the length of the bonds. This occurs as the higher bond order causes an increased amount of attraction between the atoms, resulting in a shortened bond. Bond length is measured in pm ( 1 picometer → 10-12 meters), or Å ( 1 angstrom→10-10 meters).

Bond Length Example:

What is bond length

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