Transcript Key Scientistsx

Chapter 4
Sections 1 and 2
Atomic History and Structure
Of the 11 key scientists discussed,
which do you believe had the most
important contribution? Why?
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Do Now
• Smallest particle of an element
• All matter is created of atoms
• Comes from the Greek word atomos
• “indivisible”
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The Atom
• Greek philosopher
• First to propose the
idea of the atom’s
existence
• Theorized that the
atom is indivisible
and indestructible,
but had no
experimental
evidence
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Democritus (460 – 370 B.C.E.)
• English chemist and
teacher
• Pioneered the
modern discovery
process about atoms
• Transformed
Democritus’s
theories on atoms
into an actual
scientific theory
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John Dalton (1766-1844)
Dalton’s Atomic Theory
1. All elements are made up of atoms, which are small
invisible particles
2. Atoms of the same element are identical
3. Atoms of different elements can chemically
combine in whole-number ratios to form
compounds
4. Chemical reactions occur when atoms are
separated, joined together, or rearranged; but
atoms cannot change into another element because
of a reaction
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Published 1808
• Studied the way
elements combined
in chemical reactions
and the ratio in
which they combined
• Ex: Liquid mercury
• All drops have the
same properties
• All drops are made of
the same atoms
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How did Dalton create his theory?
• Mostly!
• However atoms are now known to be divisible
• They are comprised of smaller subatomic
particles known as protons, neutrons, and
electrons
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Is Dalton’s theory accepted today?
• A Russian chemist
and teacher
• Arranged the then 60
known elements in
order by increasing
atomic mass
• Created the first
periodic table in
1869
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Dmitri Mendeleev
• Discovered the
electron in 1897
• Passed electric
current through a
tube filled with gas
and observed a
glowing beam known
as a cathode ray
• Concluded all atoms
contained electrons
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J. J. Thomson (1856-1940)
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Cathode
Ray
• Electrons pass from the negatively charged cathode to the
positively charged anode
• Created a glowing beam of light
• Proved that negative particles (electrons!) were being
attracted to the positive anode
• Thomson believed
electrons were
evenly distributed
throughout the atom
• The atom was also
filled with positively
charged material
• This model was later
disproved
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“Plum-Pudding Model” of the Atom
• U.S. Physicist
• Calculated the charge
of an electron in
1909
• 1.60 x 10-19 Coulomb
• Also calculated the
mass of the electron
• 1/1840 the mass of a
hydrogen atom
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Robert A Milikan (1868-1953)
• Discovered positively
charged subatomic
particles called
protons in 1886
• Used a variation of the
cathode ray
• Calculated the mass
of the proton
• 1840 times the mass
of the electron
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Eugen Goldstein (1850-1930)
• Confirmed the
existence of neutrally
charged particles, the
neutron, in 1932
• Calculated that
neutrons had a mass
equal to the mass of
a proton
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James Chadwick (1891-1974)
How do we describe the structure
of the atom?
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• Atoms are made of protons, neutrons, and
electrons
• How are they put together to make an atom?
• Former student of
J. J. Thomson
• Devised the gold-foil
experiment in 1911
• Created a new
atomic model based
on his findings
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Ernest Rutherford (1871-1937)
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Gold Foil
Experiment
• Alpha particles (Helium atoms without two electrons)
were shot at a sheet of gold foil
• Some particles passed through the foil but a few were
deflected
• Why??
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The nuclei of the gold atoms in the foil deflects the small
alpha particles; the empty space surrounding the nuclei
lets other alpha particles pass through.
• The atom is mostly empty space
• All the positive charge and almost all the mass of the
atom is contained in the nucleus
• The nucleus is made of the protons and neutrons
• Electrons are distributed around the nucleus
• Electrons occupy almost all of the atoms volume
• Rutherford’s model is still being revised today!
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The Rutherford Atomic Model
• Danish student of
Rutherford
• In 1913 he proposed
that an electron is
found only in specific
circular paths known
as orbits around the
nucleus
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Niels Bohr (1885-1962)
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The Bohr Model
• French Physicist
• In 1923, he proposed
that all moving
particles, including
electrons, had
properties of waves
• Influenced
Schrödinger's work
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Louis de Broglie (1892 – 1987)
• Austrian physicist
• Devised and solved a
mathematical
equation to describe
the true behavior of
electrons in atoms in
1926
• Known as the
quantum mechanical
model
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Erwin Schrödinger (1887-1961)
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Modern Day Model of the Atom
Scientist Pamphlet Project!
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Where they were born/where they lived
Family life
How they got interested in science
Any other discoveries they may have made
Prizes, awards, honors, and recognitions they got before and after
death
• Any fun facts!
• Make sure that your information and drawings cover the
entire pamphlet!
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• Choose one of the 11 key scientists you researched today
to create a pamphlet on
• Do further research and include lots of information on
your chosen scientist such as