John Dalton
THE FATHER OF MODERN ATOMIC THEORY
The life of John Dalton
•Born September 5th or 6th, 1766, in Eaglesfield, England. Youngest of three surviving boys
•Began his career as a teacher at age 12, which he stuck with for most of his life (worked on a
farm at age 14, but he didn’t stay with it for too long)
•After 10 years of teaching, Dalton moved to Manchester and joined the Manchester Literary and
Philosophical Society
•He and one of his brothers was born colorblind, which is what he wrote his first paper on
•Theorized that colorblindness was hereditary, which was late proven true
•He loved meteorology, which led to his research on atmospheric pressure
•Had two mentors that assisted him with learning about meteorology- Elihu Robinson and John
Gough. They helped with the science and math of it, respectively.
Discoveries & When They Happened
•In early 1800, Dalton experimented with and studied the nature and
chemical makeup of air, and learned that it was not a chemical solvent.
Instead, it was a "mechanical system composed of small individual
particles that used pressure applied by each gas independently."
•1803- Dalton discovered and created “Dalton’s Law of Partial Pressures”.
This law says that the total pressure of a mixture of non-reacting gases
amounts to the sum of the partial pressures that each individual gas
exerts while occupying the same space.
Discoveries, Part II
•In 1808, published “A New System of Chemical Philosophy”, which included
many of his findings that still influence chemistry today (including associating
atoms with weight and his atomic theory)
•1810, released an appendix for his book that expanded on atomic theory and
atomic weight
Dalton’s Atomic Theory
•All matter is made of atoms. Atoms are indivisible and indestructible.
•All atoms of a given element are identical in mass and properties.
•Compounds are formed by a combination of two or more different kinds of
atoms.
•A chemical reaction is a rearrangement of atoms.
•Atoms can neither be created nor destroyed.
Dalton’s Atomic Theory II
•A few of Dalton’s procedures for his atomic theory are known.
•All matter is made of atoms. Atoms are indivisible and indestructible – Dalton based this on
the Law of Conservation of Matter and hundreds of years of evidence. Since his time, this has
been altered to be more accurate by saying "Atoms cannot be created, destroyed, or
transformed into other atoms in a chemical change".
•All atoms of a given element are identical in mass and properties – Dalton knew that atoms of
the same element had identical weights, while atoms of different elements have different
weights. Since then, we have discovered that atoms of the same element do have slightly
different masses. We now know that "Elements are characterized by the nuclear charge of their
atoms".
Dalton’s Experiment
•Not all of Dalton’s experiments for his atomic theory are known
•There is one experiment he conducted during his meteorology studies
•Dalton wondered how air and water could exist in the same space at the same
time
•Inferred that, if the water and air were composed of different particles, then
evaporation might be seen as a mixing of air and water particles
•Developed hypothesis that the sizes of the particles making up different gases
must be different
Dalton’s Analysis and Conclusion
•Of course, John Dalton’s analysis was his thoughts about water vapor and the
air, and their different compositions.
•His conclusion was his atomic theory, the aforementioned set of five rules
regarding atoms and matter.
•Thanks to Dalton, there’s a lot of information about modern atomic theory that
otherwise could have taken much longer to discover than it did.