Dalton’s Theory and the Water Molecule

Dalton’s atomic theory states that a molecule of water is composed of atoms from different elements-specifically, two hydrogen atoms and one oxygen atom. According to Dalton, all water molecules are made up of these two types of atoms in a fixed ratio: for every one atom of oxygen, there are two atoms of hydrogen

. This means:

• Water molecules always consist of two hydrogen atoms and one oxygen atom.
• All water molecules are identical in their atomic composition-no matter where the water comes from, it will always have this 2:1 ratio of hydrogen to oxygen

• The atoms themselves are indivisible and indestructible in chemical reactions, and they combine in whole-number ratios to form compounds like water

Dalton’s theory also emphasized that compounds (like water) are formed by the combination of atoms of different elements, and that the composition of a compound is always constant (law of constant composition)

. Summary Table: Dalton’s View of Water

Feature| Dalton’s Theory Description
---|---
Composition| 2 hydrogen atoms + 1 oxygen atom per molecule
Ratio| Always 2:1 (hydrogen:oxygen)
Identity| All water molecules are identical in composition
Atoms| Indivisible, indestructible, and rearranged in reactions
Law applied| Law of constant composition

Dalton’s atomic model was a foundational step in chemistry, even though his original assumption about water’s formula (initially thought to be HO) was later corrected to H₂O as more accurate measurements and Avogadro’s work clarified the true composition

. Nonetheless, Dalton’s theory correctly established that water is always made from hydrogen and oxygen atoms in a fixed, whole-number ratio