Hydrogen bonding is a special type of intermolecular force (attraction between molecules) that occurs when a hydrogen atom covalently bonded to a highly electronegative atom is attracted to another electronegative atom in a nearby molecule.
Key Features of Hydrogen Bonding:
- Requirement – It forms when hydrogen is attached to strongly electronegative atoms like fluorine (F), oxygen (O), or nitrogen (N).
- Partial charges – The electronegative atom pulls electrons strongly, leaving hydrogen with a partial positive charge (δ+) and the electronegative atom with a partial negative charge (δ–).
- Attraction – The δ+ hydrogen is attracted to a lone pair of electrons on another electronegative atom, creating a hydrogen bond.
- Strength – Stronger than Van der Waals forces but weaker than covalent or ionic bonds.
- Types –
- Intermolecular hydrogen bonding: between molecules (e.g., between water molecules).
- Intramolecular hydrogen bonding: within the same molecule (e.g., in o-nitrophenol).
Examples:
- Water (H₂O): Extensive hydrogen bonding gives water its high boiling point and surface tension.
- Hydrogen fluoride (HF): Forms strong hydrogen bonds, leading to higher boiling points.
- DNA: Base pairs (A–T and G–C) are held together by hydrogen bonds.
- In simple words: Hydrogen bonding is the “extra strong attraction” between a hydrogen atom attached to F, O, or N and another nearby F, O, or N atom.