Hydrogen bonding
The dipole, reaching out. Water's O–H bond leaves the hydrogen with a strong, naked δ+ — no inner electrons to hide behind — and the next molecule's oxygen offers a lone pair (δ−). The two attract: O–H···O, a hydrogen bond. It is weak — about 20 kJ/mol, a twentieth of the covalent bond inside the molecule — but there are billions of them, and that is enough to make water liquid where it should be gas, to hold ice open so it floats, and to zip and unzip DNA. Heat it past 100° and watch them snap.
Bridge-Burners LLC · Fiddler · δ+H···lonepair · ~20 kJ/mol · one molecule → the ocean · anchor: AKASHA
State
phaseliquid
H-bonds intact~3.5 / molecule
density1.00 g/cm³
notedenser than ice
Strength ladder
| covalent O–H | ~460 kJ/mol (inside molecule) |
| hydrogen bond | ~20 kJ/mol · O···O 280 pm |
| dipole–dipole | ~5–15 kJ/mol |
| London (vdW) | ~1–5 kJ/mol |
What it buys
| boiling pt | 100°C — without H-bonds ≈ −80°C |
| ice floats | 0.92 vs 1.00 g/cm³ (open lattice) |
| DNA | A=T 2 H-bonds, G≡C 3 — zips/unzips |
Status discipline
Literalδ+ H on O/N/F–H attracts a lone pair on O/N/F; ~20 kJ/mol; each water bonds ~4 (2 donor H + 2 acceptor pairs); ice's open lattice floats; H-bonds lift water's BP ~180°C.
BridgeThe water dipole reaching the next molecule; one molecule → bulk water, ice, biology; the strong end of intermolecular forces.
SpeculativeMostly electrostatic but with some covalent/charge-transfer character (debated); point-charge cartoon schematic. Liquid water is dynamic — "4" is the ice ideal, liquid averages ~3.4–3.6 on picosecond lifetimes.