Transcript History - E. R. Greenman

History of the Atom
Democritus of Abdera
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Democritus: 460-370 BCE
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Greek mathematician and philosopher
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Co-author (with Leucippus) of the idea that all
matter is made of small, indivisible particles
called atoma
Proposed that the behavior of substances were
due to the type of atom
Alchemists
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Great many 'experiments' to try to convert one
element to another
Many discoveries, but very secretive
Robert Boyle
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Robert Boyle: 1627-1691
Performed experiments with controls and
published detailed results
1661: Published claiming that Aristotle's ideas
were incorrect, and that some 'elements' (like
mercury) did not contain the 4 Aristotlean
elements (earth, air, fire, water)
Antoine Lavoisier
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Lavoisier: 1743-1794
Experimented and established the Law of
Conservation of Mass
Investigated combustion and cellular respiration
in terms of energy and mass
Charles de Coulomb
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Coulomb 1736-1806
Developed Coulomb's Law, the definition of
electrostatic force
Joseph Proust
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Proust: 1754-1826
Controversy with another scientist (Berthollet)
led him to discovery of the Law of Definite
Proportions (sometimes called Proust's Law)
A chemical compound always contains the
same proportion of elements by mass
There are exceptions, which are called nonstoichiometric (or Berthollide) compounds
John Dalton
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Dalton: 1766-1844
Law of Multiple Proportions (1803): elements
combine in mass ratios of small whole numbers.
Elements may combine with the same element
in different proportions to make a different
compound.
Atomic theory contains 4 hypotheses
Atomic Theory
1. Elements are made of small particles called
atoms. (Dalton viewed atoms as small spheres
of differing characteristics.)
2.All atoms of an element are identical. All atoms
of one element are different from atoms of other
elements.
3.Compounds are made of atoms of more than
one element. The ratio of the elements is a
simple fraction.
4.A chemical reaction involves separation,
combination or rearrangement of atoms.
James Clerk Maxwell
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1831-1879
Showed that
electricity and
magnetism were
related, and were
related to atoms
Predicted that
accelerating charges
would make waves
(electromagnetic
radiation)
Cathode Ray Tube Experiments
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Glass tube with wire at each end; as much air
pumped out as possible
Charge passed across tube makes fluorescent
glow
William Crookes
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Tube coated with fluorescent material can be made
to glow in one focused dot
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Rays travel in straight lines
Ray carries negative charge
Joseph John Thomson
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1856-1940
Used a study of the
cathode ray tube to
determine the
presence of electrons
1897
Suggested the plum
pudding model of the
atom and the
existance of isotopes
Won the Nobel Prize
in Physics in 1906
J. J. Thomson’s 4 Experiments
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Used magnetic field to show cathode rays had
negative charge
Used electric charge to show cathode rays were
particles with negative charge
Used varying electric currents to determine charge to
mass ratio
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Either particles very small or
Carried huge charge
Evidence suggested particles very small and came
from atom
Robert A. Millikan
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1858-1953
Used the 'falling drop
method' to determine the
charge of the electron (1.6022 x 10-19 C) and
mass of electron as 9.10 x
10-28 g
Investigated photoelectric
effect and spectroscopy of
elements
Won the Nobel Prize in
Physics in 1923
Wilhelm Röntgen
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1825-1943
Rays produced by
cathode ray tube
interaction with other
matter could pass
through objects, affect
photographic plates
and cause some
materials to fluoresce
(X-rays)
Nobel Prize in
Physics in 1901
Antoine Henri Becquerel
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1852-1908
Investigated possible link
between X-rays and
natural
phosphorescence
Discovered that the rays
emitted by uranium were
different from X-rays
Nobel Prize in Physics
1903 (shared with Pierre
and Marie Curie)
Marie Curie
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1867-1934
Worked with huband
Pierre to study
radioactivity
Isolated elements
polonium and radium
Shared Nobel Prize in
Physics 1903, won
Nobel Prize in Chemistry
1911 for work with
radioactive elements.
Ernest Rutherford
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1831-1937
Investigated release and
measurement of different
forms of radiation from
elements (α, β, γ)
Gold foil experiment with
Geiger and Marsden led
to new model of an atom
with dense central
nucleus and vast empty
areas
Nobel Prize in Chemistry
1938
Model of the atom in the early 1900s
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Nucleus: has positive charge, very small, but
very dense
Proton: same charge as electron, but opposite.
Mass=1.67262 x 10-24 g
Vast empty space around nucleus contains
electrons
James Chadwick
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1891-1974
Discovered the
neutron and worked
on fission of atoms
Discovery of neutron
(mass=1.67493 x 1024 g) explained the
mass problem of
many atoms
Nobel Prize in
Physics 1935
Mass and Atomic Number
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Each element's atoms have a specific number
of protons in the nucleus (Z=atomic number)
For a neutral atom, the number of protons is
equal to the number of protons
The mass number (A) is the number of protons
plus the number of neutrons (the number of
particles in the nucleus).
Some atoms of the same element have different
A values. This means they have different
numbers of neutrons. They are called isotopes.
Isotope notation
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Isotope notation is
used to represent an
isotope.
Z, A and symbol of
element are
represented.
Isotope notation can
be used to determine
the number of
protons, neutrons and
electrons in an
isotope.