Atom's structure

Dalton's atomic model

Dalton's atomic model

According to Dalton's atomic theory, the matter is made up of indivisible particles called atoms. The atoms of different chemical elements are different from each other. According to this atomic theory, compounds are formed due to the combination of two or more elements in a simple proportion. Dalton also found the relative masses of the atoms.

In 1808, John Dalton developed and published his theory of the atom, which took up the old ideas of Leucippus and Democritus. However, this time it was based on a series of scientific laboratory experiences.

Dalton was a member of the Manchester Literary and Philosophical Society since 1793. His book “A New System of Chemical Philosophy” was the first application of atomic theory to chemistry.

Modern atomic theory is based on Dalton's theory, but parts of it have been changed.

What is John Dalton's atomic theory based on?

Dalton's atomic theory is based on four assumptions;

  • Chemical elements are made up of tiny, indivisible, and indestructible particles called atoms.

  • All the atoms of a particular element are identical with the same atomic mass.

  • The atoms of different elements vary in size and atomic mass.

  • Atoms of different elements can combine to form other chemical compounds.

  • Chemical reactions consist solely of the separation, union, or rearrangement of atoms.

Dalton's atomic theory also allows a better description of the problems of chemical change:

  • Law of conservation of mass: The sum of the masses of the substances that react in a chemical reaction is equal to the sum of the masses of the substances (products) released. The sum of the atomic weights remains constant.

  • The Dalton’s law of multiple proportions: If two elements make up more than one compound, there is a simple relationship between the different amounts of the two elements combined, which can be expressed as whole numbers by weight. For example: in H2O, while 2g of hydrogen atoms and 16g of oxygen atoms are combined, in OH, 1g of hydrogen and 16g of oxygen are combined. If we compare 2g of hydrogen and 1g of hydrogen combined with the same amount of oxygen in both compounds, we get the number 2.

What shortcomings and errors did Dalton's atomic theory have?

  • Not all the atoms of an element are the same since an atom can have several isotopes.

  • The atoms are not filled inside.

  • The smallest known particle is not an atom.

  • Just as not all the atoms of an element are the same, not all the compound molecules are the same.

  • Atoms can break down as a result of nuclear reactions.

  • One of the events that contradict the view that atoms cannot be fragmented and rebuilt is that atoms radiate alpha particles.

Publication Date: April 22, 2021
Last Revision: April 22, 2021