Bond Energy and Bond Length — Overview & Importance

Bond Energies and Bond Lengths:

• Bond Energy: The amount of energy required to break a chemical bond.

• For an ionic bond, the bond energy is called the lattice energy. It's determined by the Born-Haber cycle.

• For covalent bonds, you will sometimes see it called bond dissociation energies.

• Bond Length: The distance between the nuclei of two bonded atoms.

$\color{#3db917}{Important}$ $\color{#3db917}{note}$: The smaller the bond length, the greater the bond energy!

Bond Energy:

• To determine the bond energy, we measure the heat required to break the molecule/compound into its individual atoms.

• It is measured at standard temperature and pressure (STP), with the substance in the gas phase.

• Computational chemists will sometimes calculate the value at absolute zero instead of STP.

• The units of bond energy are kilojoules per mole (kJ/mol).

• Bond energy relates to enthalpy. It typically requires energy to break a bond and releases energy to form a bond.

• Bond energy is the reverse of the standard enthalpy of formation.

• Average bond energy is the average of individual bond energies of a specific bond across numerous molecules.

Bond Length:

• On the periodic table, bond length increases down a group, and decreases across a period.

• Bond length depends on both the elements involved in the bond as well as the type of bond (as in single, double, or triple bonds).

• Having more bonds between two atoms causes the atoms to be pulled closer together.

• In order from shortest to longest: Triple bonds < double bonds < single bonds Measured in Ångstrom (Å) or picometers (pm) (1 Å = 100 pm).

• Bond length directly relates to bond strength.

Bond Energy and Bond Length

(Video) Bond Order, Bond Length and Bond Strength

By: chemistNATE

This video goes into detail about the differences between different types of chemical bonds (single, double, and triple bonds) and their energies. This video also goes into detail about bond order which helps better distinguish between the different types of bonds. This video does a great job of explaining these topics in detail! He'll show you an example comparing the carbon-oxygen bonds in carbon monoxide, carbon dioxide, and methanol. He also shows you an example of acetic acid and the acetate ion to demonstrate resonance.

After watching this video, you'll have an excellent understanding of this topic. For extra practice, try thinking about considerations required to determine the bond energy of water molecules (hint! think about resonance).

Bond Energy and Bond Length: Connection between bond energy, bond length, and bond strength

The triple bond is shorter than a double bond, and a double bond is shorter than a single bond. Weaker bond strength results in the bond having less bond energy. On the other hand, stronger bond strength results in the bond having stronger bond energy.