Water is a molecular compound made from two hydrogen atoms and one oxygen atom. The molecule is bent rather than linear. That geometry, together with polar O–H bonds, gives water a molecular dipole and underlies much of its intermolecular chemistry.
The three atoms in a water molecule are not arranged in a straight line. Oxygen sits at the vertex of a bent H–O–H shape. That simple piece of geometry is enough for a first reading; the numerical angle belongs one level deeper.
Each O–H bond is polar because oxygen attracts the bonding electrons more strongly than hydrogen. Because the two bonds point in different directions rather than directly opposite one another, their dipole contributions do not cancel. Water therefore has a net molecular dipole.
The angle is measured at oxygen between the two O–H bond directions. Experimental gas-phase data give an equilibrium angle very close to 104.5°. The symbol ≈ is deliberate: 104.5° is a rounded experimental value, not a mathematical constant for every instantaneous water geometry in every environment.
It is the angle between the two O–H bonds at oxygen. It should not be interpreted as a fixed angle between neighbouring molecules in liquid water. In the liquid, hydrogen bonding and molecular motion continually perturb local geometries.
The subscripts count atoms in one molecule: two H atoms for every one O atom. The mass percentages look very different from the atom percentages because oxygen atoms are much heavier than hydrogen atoms.
An O–H bond inside one H₂O molecule is covalent. A hydrogen bond is an attractive intermolecular interaction involving the hydrogen of an O–H group and an electron-rich site on another molecule. Keeping those two bond types separate prevents a common conceptual error.
Water molecules can both donate and accept hydrogen bonds. The resulting network changes continuously in the liquid, yet it strongly influences boiling, surface behaviour, solvation and the structures adopted by ice.
These are collective properties of many interacting molecules; they cannot be inferred from a single H₂O formula alone.
Proton transfer between water molecules produces hydronium and hydroxide ions. The equilibrium lies very far toward neutral water under ordinary conditions, but it is chemically fundamental.
A tetrahedral electron-domain picture is a useful starting model, but lone-pair electron density and the details of the molecular wavefunction alter the equilibrium geometry. Experiment gives an angle close to 104.5° for gas-phase H₂O.
Electrostatics are important, but modern descriptions also include polarization and orbital contributions. “Partial charges attract” is useful at introductory level, not a complete quantum-mechanical account.
No. Four is a useful tetrahedral-network motif, especially in ice and local liquid structures, but the liquid network fluctuates continuously and individual molecules do not carry a permanently fixed set of four hydrogen bonds.
| Molecular formula | H₂O |
|---|---|
| Molar mass | 18.0153 g/mol |
| CAS Registry Number | 7732-18-5 |
| PubChem CID | 962 |
| Standard InChI | InChI=1S/H2O/h1H2 |
| Molecular geometry | Bent; experimental H–O–H angle ≈104.5° in the gas phase |
Two hydrogen atoms form the O–H bonds in each water molecule.
Oxygen forms the two O–H bonds and carries the lone-pair electron density central to water's geometry and hydrogen bonding.
See why polar bonds produce no net molecular dipole when a molecule is linear and symmetric.