John Dalton (1766-1844) began teaching at age 12 at his Quaker boarding school in Kendal, England. Ten years later, he moved to Manchester where he delivered his first scientific paper. The paper was on color blindness, an affliction that affected Dalton himself. In fact, even today red-green color blindness is referred to as “Daltonism”.
Dalton possessed exceptional observational skills. In fact, for a time he became so interested in the weather that he began tracking and documenting it on a daily bases from 1787 until his death. He was not, however, known for being overly skilled in the laboratory. Sir Humphry Davy, another famous chemist at the time once said that Dalton “almost always found the results he required, trusting to his head rather than his hands.”
In 1808, John Dalton published a “New System of Chemical Philosophy”. In it, he combined all of his theories into what we now call, “Dalton’s Atomic Theory”. Dalton’s atomic theory is based on three big ideas:
(1) The Conservation of Mass Law
Mass cannot be created or destroyed in a chemical reaction.
(2) The Law of Definite Proportions
Any sample of a given compound will always contain the same proportion of elements by mass.
(3) The Law of Multiple Proportions
When atoms of two elements combine to form different compounds, their mass ratios are small whole number multiples of each other.
Dalton’s Atomic Theory
(1) Matter is made up of tiny, indivisible particles called atoms.
(2) Atoms of a kind, meaning atoms having the same size, mass, and chemical properties, make up the elements.
(3) Atoms of different elements can combine with atoms of other elements to form chemical compounds.
Long before Dalton’s Atomic Theory, a Greek philosopher named Democritus first proposed the idea of atoms. He noticed that the sand on the beach appeared to be continuous until he became close enough to it where he could observe that it was actually made up of tiny individual particles. From this simple observation, he reasoned that maybe the entire physical world is also made up of tiny particles.
2000 years later, John Dalton had laid out the definitive proof that the atoms that Democritus had imagined were in fact real. In doing so, he laid a firm foundation for our understanding of the microscopic world today.