Dalton’s Atomic Theory
In 1808, Dalton presented his theory of atoms:
Paraphrasing:
1) Each element is made up of tiny particles called atoms
2) The atoms of a given element are identical; the atoms of different
elements are different in some fundamental way or ways
3) Chemical compounds are formed when atoms of different elements
combine with each other. A given compound always has the same
relative numbers and types of atoms
4) Chemical reactions involve reorganization of the atoms – changes in
the way they are bound together. The atoms themselves are not
changed in a chemical reaction
Beyond this, he made an important assumption;
That nature was as simple as possible
Although this assumption was inaccurate it did lead him to some useful
results
He was able to prepare the first table of atomic masses (weights)
The large step in science was made by Joseph Gay-Lussac (1809)
He observed that at the same temperature and pressure 2 volumes of
hydrogen gas reacted with 1 volume of oxygen gas
This work was closely followed by Amadeo Avogadro (1811) who proposed
(from Lussacs’ results) that:
At the same temperature and pressure, equal volumes of different gases
contain the same number of particles (Avogadro’s Hypothesis)
Avogadro’s Hypothesis led to the following relation:
If;
2 volumes of hydrogen + 1 volume of oxygen → 2 volumes of water
