Intramolecular Force & Potential Energy (College Board AP Chemistry)

• A potential energy diagram represents the potential energy as a function of internuclear distance
  • The distance at which the potential energy is at a minimum is the bond length of the covalent bond
  • The difference between the minimum potential energy and zero is the bond energy, the amount of energy required to break the covalent bond

Potential Energy Diagram

Potential energy diagram of hydrogen gas (H₂) showing a minimum potential energy of -436 kJ/mol which corresponds to a bond length of 74 pm

• When two atoms are far away
  • There is little attraction between the positively charged nucleus of one atom and the negatively charged electrons of the other atom
  • The potential energy is near zero
• When two atoms are very close
  • The two positively charged nuclei and the two negatively charged electron clouds strongly repel one another
  • The potential energy is very high
• When two atoms form a stable covalent bond
  • The attractive and repulsive forces between the two atoms are balanced
  • The potential energy is at a minimum.

• As atomic radius increases, bond length increases
  • Bond length is typically reported in units of picometers (pm)
  • A picometer is 1 x 10^-12m

Bond length in halogens

Diagram showing that the bond length of diatomic halogen molecules increases with increasing atomic radius

• Bond order indicates the number of electron pairs that are shared between two atoms
• As bond order increases, bond length decreases while bond energy increases