Question

Explain Dalton's atomic theory.

Answer 1

Dalton's Atomic Theory

• John Dalton proposed a theory that gives a simple description of matter as composed of atoms.
• Dalton's theory was the first to describe all matter in terms of atoms and their properties.
• His theory is based on the law of conservation of mass and the law of constant composition.
• Some parts of Dalton's theory had to be modified based on the discovery of subatomic particles and isotopes.

Law of conservation of mass

• The law says that Matter is not created or destroyed in a closed system.
• In a chemical reaction, the mass of each element must be the same as in the starting materials and the products.

Law of constant composition

• The law states that pure compounds will always have the same proportion of the same elements.

Postulates

• All matter in the universe is made of very tiny particles known as atoms.
• Atoms cannot be created or destroyed in a chemical reaction.
• Atoms are indivisible particles.
• In a given element, atoms are identical in mass and chemical properties but atoms of two different elements differ in mass and chemical properties.
• Atoms combine in the ratio of small whole numbers to form a compound.
• The relative number and kinds of atoms are constant in a given compound.

Limitation

• It failed to explain the existence of allotropes.
• Atoms can be subdivided into electrons, protons, and neutrons.
• Smallest unit capable of independent existence is not an atom, but a group of atoms.