Dalton's Atomic Theory (1808)

  1. Elements are made up of tiny [indivisible and indestructible] particles called atoms.
  2. Atoms of a given element are identical. Atoms of different elements differ from each other in some fundamental way.
  3. Compounds are formed when atoms of different elements combine. A given compound always has the same relative number and type of atoms. [Another phrasing -- These combinations occur in simple whole number ratios (e.g. 1;1, 1:2)]
  4. Chemical change occurs when the atoms are arranged in new ways.

Law of Conservation of Mass (or matter) - Mass is neither created nor destroyed in a chemical reaction.

Law of Definite Proportions - A given compound always contains the same proportion of elements by mass.

Law of Multiple Proportions - When two elements form more than one compound, the ratios of the masses of the second element that combines with one gram of the first element are always small whole numbers.

Avogadro's Hypothesis - At the same temperature and pressure equal volumes of gases contain the same number of particles.
bulletHypothesis proposed to explain the findings of Gay-Lussac. Gay-Lussac measured volumes of gases that would react with each other at a given temperature and pressure.


1. How does Dalton's Atomic Theory explain the law of conservation of matter, law of multiple proportions, and the law of definite proportions?

2. How has Dalton's Atomic Theory been modified?