What it shows
In a water molecule the oxygen pulls the shared electrons towards itself, so each H is slightly positive and the O slightly negative, with two lone pairs. The slightly positive H of one molecule is attracted to a lone pair on the O of the next: that attraction is a hydrogen bond, drawn here as a dashed blue line from H to O. It is much weaker than the O–H bond inside the molecule, but strong enough to change how water behaves.
- In liquid water the molecules move and turn all the time. Hydrogen bonds keep breaking and re-forming; the colder the water, the more of them hold at any moment.
- In ice every molecule is locked in place with four hydrogen bonds: it gives two (through its H atoms) and takes two (on its lone pairs). That holds the molecules apart in an open lattice, so the same box holds fewer molecules: ice is less dense than water and floats.
The second card sorts molecules: a hydrogen bond needs an H on N, O or F and a lone pair on N, O or F.
It follows hydrogen bonding in chemical bonding and states of matter in Class 11 chemistry, and the unusual properties of water met in Classes 9 and 10. The states of matter particle box shows solids, liquids and gases in general, dipole polarity shows why the O–H bond is polar, and the heating curve shows how much energy it takes to break all those bonds when water boils.
How to use it
- Slide the temperature. Above 0 °C you see liquid water; at 0 °C and below, ice. The big line counts the hydrogen bonds in the box right now.
- Pause to freeze the picture and count bonds yourself. The facts show molecules in the box and bonds per molecule.
- Tap a molecule in the sorter to see whether it can hydrogen bond, and why.
Worked example
In the ice picture the box holds 6 × 6 = 36 molecules. Each gives 2 hydrogen bonds, so there are 36 × 2 = 72 bonds, and each molecule takes part in 4 of them (2 given + 2 taken). The liquid box holds 40 molecules, about 11% more, because molecules that are not locked in the lattice can pack closer. (In real water the difference is about 9%.)
Water boils at 100 °C. Hydrogen sulfide, H₂S, is heavier but has no real hydrogen bonds and boils at about −60 °C. The hydrogen bonds in water are why it is a liquid at room temperature.
Check yourself
Three questions: whether a molecule can hydrogen bond, how many bonds each molecule has in ice, and why ice floats. Nothing is saved.
FAQ
Is a hydrogen bond a real bond? It is an attraction between molecules, about a tenth as strong as an O–H bond, but the strongest of the forces between neutral molecules.
Why is the ice drawn as squares? Real ice is a 3D lattice of tetrahedra. A flat screen cannot show four neighbours at 109.5°, so the model squares them off; the bond count is the same.
Is this from my textbook? It covers the standard school topic with its own examples and pictures. It is an independent study aid, not part of NCERT.
Where the numbers come from
- Standard chemistry: hydrogen bonds between H on N, O or F and a lone pair on N, O or F; the open hydrogen-bonded lattice of ice (each molecule giving two and taking two bonds); ice about 9% less dense than water. Written for fibub; the model is a flat teaching picture, not a molecular simulation. No textbook text, figures or exercises are used.
- Bond-counting geometry checked by hand: in the flat ice model every molecule gives exactly 2 and takes exactly 2 hydrogen bonds (2N bonds in a box with wrap-around), and the donor/acceptor sorting matches the standard textbook list.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-09.