Intermolecular Forces: Hydrogen Bonding

Intermolecular Forces: Hydrogen Bonding

Hydrogen Bonding

Understanding Hydrogen Bonding

  • Hydrogen bonding is a special type of dipole-dipole interaction between molecules, not within a single molecule.
  • This particularly strong form of bonding only happens when hydrogen is bonded to one of three very electronegative elements: fluorine (F), oxygen (O), or nitrogen (N).
  • The large difference in electronegativity results in a polar bond, with significant charge separation and a dipole moment.
  • The hydrogen on one molecule then forms a bond with a lone pair of electrons on a neighbouring molecule (F, O or N).

Characteristics of Hydrogen Bonding

  • Hydrogen bonds are significantly stronger than other types of intermolecular forces such as London dispersion forces and dipole-dipole interactions.
  • Despite being strong, they are still much weaker than covalent bonds within a single molecule.
  • Hydrogen bonding leads to higher melting points, boiling points, and enthalpies of vaporisation for compounds compared to similar-sized compounds that do not exhibit hydrogen bonding.

Effects of Hydrogen Bonding

  • Solubility: Many compounds, like alcohols and carboxylic acids, are soluble in water due to hydrogen bonding with water molecules.
  • Boiling and melting points: Compounds exhibiting hydrogen bonding tend to have higher boiling and melting points due to the extra energy required to disrupt hydrogen bonds.
  • Structure: Hydrogen bonding influences the structure of many complex substances, such as proteins and DNA in life sciences.
  • Density of ice: Anomalous property of water is that its solid state, ice, is less dense than liquid state due to hydrogen bonding arranging molecules into a regular open lattice structure.

Remember, a robust understanding of hydrogen bonding will be key to grasping further topics in chemistry, such as properties of water, solutions, and macromolecule structure.