Transcript Chapter 18 section 1

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
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atoma
Proposed that the behavior of substances was
due to the type of atom
Aristotle
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Greek Philosopher: 384-322 BCE
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Not an ‘atomist’
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Proposed all matter made up of 5 elements:
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Fire
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Air
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Water
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Earth
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Aether
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
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Some 'elements' (like mercury) did not contain the 4
Greek 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
John Dalton
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Dalton: 1766-1844
Law of Multiple Proportions (1803): elements
combine in mass ratios of small whole numbers.
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Small whole numbers reflect the atoms involved
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Elements may combine with the same element in
different proportions to make a different compound.
Atomic theory contains 4 hypotheses
Dalton’s 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.
Joseph John Thomson
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1856-1940
Used a cathode ray
tube to determine the
presence of electrons
1897
Suggested the plum
pudding model of the
atom and the
existence of isotopes
Won the Nobel Prize
in Physics in 1906
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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1825-1923
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 husband
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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1871-1937
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
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Model:ruther14.swf
Nobel Prize in Chemistry
1908
Model of the atom in the early 1900s
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Nucleus: has positive charge, very small, but
very dense
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Proton: same charge as electron, but opposite.
Mass=1.67262 x 10-24 g
Vast empty space around nucleus contains
electrons
Where are the electrons?
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Niels Bohr: 1885-1962
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Collaborated with Rutherford
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Used emission spectra to
propose Bohr model of atom
1913
Electrons found in specific
‘orbits’ around nucleus
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Most of atom is empty space
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Nobel Prize Physics 1922
James Chadwick
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1891-1974
Discovered the
neutron and worked
on fission of atoms
Discovery of neutron
(mass =
1.67493 x 10-24 g)
explained the mass
problem of many
atoms
Nobel Prize in
Physics 1935
Current Model
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Based on the previous work, as well as
Einstein, Heisenberg, Born, Schrödinger and
others
Nucleus contains p+ and no
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Made of smaller particles called quarks
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uud, ddu (baryons)
Electron cloud
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e- are in areas of probability, predicted by wave
equations
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leptons
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 electrons
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.