Early Atomic Theory

John Dalton's Atomic Model

• John Dalton: First to propose a scientific atomic model in early 19th century.

Key Points of Dalton's Model

• Atoms as Indivisible Particles:

  • Proposed that all matter is composed of extremely small, indivisible particles called atoms.

• Identical Atoms of Elements:

  • Asserted that all atoms of a given element are identical in mass and properties.

  • Atoms of different elements are distinct and differ from one another.

• Whole Number Ratios in Compounds:

  • Suggested atoms combine in simple whole number ratios to form compounds.

• Chemical Reactions:

  • Indicated that chemical reactions involve only the separation, combination, or rearrangement of atoms.

  • Claimed that atoms cannot be created or destroyed in a chemical reaction.

Validity of Dalton's Model Today

• Some Points Remain Valid:

  • The concept of atoms combines in whole number ratios to form compounds

  • Chemical reactions involve rearrangement of atoms.

• Points Discarded:

  • Indivisibility of atoms and the identical nature of all atoms of an element (later evidence showed the existence of subatomic particles and isotopes).