What is Dalton’s atomic theory?
Dalton’s atomic theory explains the concepts of atoms, matter, the composition of matter, and laws of chemical combinations resulting in the formation of compounds.
These concepts are summarised in the 6 postulates of Dalton’s atomic theory.
What are the Six postulates of Dalton’s atomic theory?
Postulate 1: All matter is made up of very tiny particles called Atoms.
When we divide matter into smaller and smaller sections, at the end, we get atoms.
Postulate 2: Atoms are indivisible particles which cannot be created or destroyed in a chemical reaction.
In a chemical reaction, atoms may combine together to form new units. However, no new atoms can be created, and the existing ones cannot be destroyed.
Postulate 3: Atoms of a given element are identical in mass and chemical properties.
No atom of the same element can have different physical or chemical properties.
Postulate 4: Atoms of different elements have different masses and chemical properties.
This means, atoms of different elements are different.
Postulate 5: Atoms combine in a ratio of small whole numbers to form compounds.
We will never find half or three fourth atoms combining with the other.
For example, one unit of water always consists of two Hydrogen atoms and one oxygen atom. Also, one unit of carbon dioxide consists of one carbon and two oxygen atoms.
Postulate 5 Examples
Postulate 6: The relative number and kinds of atoms are constant in a given compound.
The number of atoms will always be constant in the unit of a particular compound.
For example, one unit of water, carbon dioxide, carbon monoxide or ammonia will always have a constant number of atoms.
Postulate 6 Examples