2.2 Intramolecular Force and Potential Energy

Bond energy and distance

Intramolecular forces (bonds within a molecule) create a potential energy well: as two atoms approach, energy decreases until reaching a minimum at the bond length (most stable distance). Pushing atoms closer than this causes strong repulsion between nuclei, sharply raising potential energy again.

Bond strength vs. bond length

Bond energy is the energy required to break a bond, equal to the depth of the potential energy well. Stronger bonds have shorter bond lengths and lower (more negative) potential energy at equilibrium. Comparing single, double, and triple bonds between the same atoms: as bond order increases, bond length decreases and bond energy increases.

Coulomb's law connection

Bond strength depends on the attraction between nuclei and shared/transferred electrons, described qualitatively by Coulomb's law: force is proportional to the product of charges and inversely proportional to the square of distance. Smaller atoms with higher charges form stronger, shorter bonds because opposite charges are closer together.

Key terms

Bond length

The internuclear distance at the potential energy minimum; the most stable distance between bonded atoms.

Bond energy

The energy required to break a bond; equal to the depth of the potential energy well.

Potential energy curve shape

Decreases as atoms approach, reaches a minimum at bond length, then rises sharply due to nuclear repulsion at shorter distances.

Effect of bond order on length/energy

Higher bond order (single→double→triple) means shorter bond length and greater bond energy.

Coulomb's law and bonding

Attractive force is proportional to charge magnitude and inversely proportional to distance squared; smaller, more charged atoms form stronger bonds.

Try an AP-style question

On a potential energy curve for two atoms, what does the minimum represent?

1. The point where the atoms repel most
2. The ionization energy
3. The bond length at the most stable separation
4. The point where no bond exists