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Dalton
What They Knew by1800
• Elements were defined as substances
which could not be broken down
further by chemical means. (Lavoisier 1775)
• There was a law of definite proportions
(elements for a given compound always
combined in the same ratio)
• There was a law of conservation of
mass. (In a chemical reaction mass is
never created or destroyed.
John Dalton
• Was born in 1766
• Was a school teacher
and later a University
Professor
• Used pre-existing laws
and his own experiments
to come up with the first
atomic theory
• Came up with the first
modern atomic theory
Dalton’s Atomic Theory 1808
• All matter is made up of small particles called
atoms.
• Atoms cannot be created or destroyed, or cut
into smaller particles
• All atoms of the same element are identical in
mass and size, but they are different in mass
and size from the atoms of other elements.
• Compounds are created when atoms of different
elements link together in definite proportions
Billiard Ball Model
• The atom, according to Dalton, was
much like a tiny billiard ball.
• An element is a substance made up
of many very tiny particles (or many
tiny billiard balls) which are all
identical.
• You could physically cut large
chunks of element into smaller
pieces (like cutting small chips of
Iron off an anvil) but you could not
chemically break that element apart.
Relative Masses
• Using electrolysis of water Dalton found
that the mass of evolved oxygen was
always 8 times that of evolved hydrogen.
• He reasoned that because Hydrogen was
the lightest element (known), he could
measure the relative masses of all the
known elements in relation to Hydrogen
• Dalton had symbols
for all the known
elements, as well as
a very primitive table
for showing the
elements in order of
increasing atomic
mass.
Last Facts
• Dalton was a reclusive character
• He rarely read any writings from other scientists
because he believed that they might “lead him
astray”
• He never got married
• 40,000 people came to his funeral
• He was colour blind
• He had a weather diary with 200,000 entries
from the time he was 22 to the time he died.