John Dalton was an English chemist, meteorologist and physicist. He
is best known for his pioneering work in the development of modern atomic
theory, and his research into colour blindness. |
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In 1800 he became a secretary of the Manchester Literary and
Philosophical Society, and in the following year he orally presented an
important series of papers, entitled "Experimental Essays" on the constitution
of mixed gases; on the pressure of steam and other vapours at different
temperatures, both in a vacuum and in air; on evaporation; and on the thermal
expansion of gases. These four essays were published in the Memoirs of the Lit
snd Phil in 1802. |
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The most important of all Dalton's investigations are those
concerned with the atomic theory in chemistry, with which his name is
inseparably associated. |
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In his first published table of relative atomic weights six
elements appear in this table, namely hydrogen, oxygen, nitrogen, carbon, sulfur, and phosphorus, with the atom of hydrogen
conventionally assumed to weigh 1. Dalton provided no indication in this first
paper how he had arrived at these numbers. However, in his laboratory notebook
under the date 6 September 1803 there appears a list in which he sets out the
relative weights of the atoms of a number of elements, derived from analysis of
water, ammonia, carbon dioxide, etc. by chemists of the time. |
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Despite the uncertainty at the heart of Dalton's atomic theory, the
principles of the theory survived. To be sure, the conviction that atoms cannot
be subdivided, created, or destroyed into smaller particles when they are
combined , separated, or rearranged in chemical reactions is inconsistent with
the existence of nuclear fusion and nuclear fission, but such processes are
nuclear reactions and not chemical reactions. In addition, the idea that all
atoms of a given element are identical in their physical and chemical properties
is not precisely true, as we now know that different isotopes of an element have
slightly varying weights. However, Dalton had created a theory of immense power
and importance. Indeed, Dalton's innovation was fully as important for the
future of the science as Antoine Laurent Lavoisier's oxygen-based chemistry had
been. |
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