Transcript John Dalton - SchoolRack

The Scientists of the Atomic
Theory
Period 1
John Dalton
(1766-1844)
Dalton
• An English chemist, meteorologist, and
physicist, from England.
• He was a teacher & public lecturer.
• Began his village school at the age of 12.
Dalton’s atomic theory
• In the early 1800’s Dalton came up with
his theory of the atom.
• He stated that elements are made up of
atoms. The reason an element is whole is
because all atoms of an element are the
exact same.
• Different atoms have different mass
• Compound have different atoms of
different elements combined together.
Atom Model
1803
Theory
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matter is composed of atoms
Atoms cannot be made or destroyed
All atoms of the same element are identical
Different elements have different types of atoms
Chemical reactions occur when atoms are
rearranged
• Compounds are formed from atoms of the
constituent elements
Errors he made
He made a mistake in assuming that the simplest
compound of two elements must be binary. He
formed atoms of each element in a 1:1 ratio.
His system of atomic weights was not very
accurate either.
• Some of Dalton's original atomic theory are now
known to be wrong, but the basic concepts
- chemical reactions can be explained by the
union and separation of atoms is what laid more
foundation of basic physics.
J.J. Thomson
Period 1
J.J. Thomson
When The Discovery Occurred
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Discovered the electron in 1897
How The Discoveries were made…
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Thomson built a cathode ray tube ending in a pair of metal
cylinders with a slit in them. These cylinders were in turn
connected to an electrometer. He wanted to see if, by bending the
rays with a magnet, he could separate the charge from the rays.
He found that when the rays entered the slit in the cylinders, the
electrometer measured a large amount of negative charge, but it
didn’t register much electric charge if the rays were bent so they
would not enter the slit. Thomson discovered that the negative
charge could not be separated from the rays (by the application of
magnetism), and that the rays could be deflected by an electric
field. He concluded that these rays, rather than being waves, were
composed of negatively charged particles.
In 1904, Thomson suggested a model of the atom as a sphere of
positive matter in which electrons are positioned by an electron
field
The Model
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In this model, the atom is composed
of electrons surrounded by a soup of
positive charge to balance the
electron's negative charge, like
plums surrounded by pudding.
Summary of his discoveries
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His experiments led to the fact that
in 1897 that atoms were made of
negatively charged particles that are
now known as electrons
Additional Info
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J.J. Thomson won the Hughes Metal
for his discovery of the electron.
He also won the Noble Peace Prize in
Physics Laureate
Credited for the discovery of the
electron and the isotope
Thomson called electrons corpuscles,
the name electron came from G. J.
Stoney.
Ernest Rutherford
Known as the “Father of nuclear physics”
Rutherford’s Experiment
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Rutherford took a radioactive substance put it in a
lead box and placed a thin piece of gold foil in the
middle of a detecting screen.
When Rutherford was performing his experiment he
saw that many particles went through the screen; but
some of the particles would bounce back (hitting the
nucleus), not going straight through the screen.
Rutherford performed his experiment in 1911
Rutherford’s Experiment
Concluding
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Rutherford determined that because most of
the particles went through the atom, it was
made of a “hollow space.”
Concluding that atom was an “empty space”
but there was a + charged nucleus in the atom.
“Planetary Model”
Niels Bohr
Makeda Smith Chemistry I 10.23.07
Bohr’s Atomic Discovery
 Niels Bohr discovered the quantum model which is explained the
theory that electrons were found in energy levels (orbits) around the
atom’s nucleus.
 Bohr made this discovery in the year 1913 and is said to have won a
Nobel Prize in 1922.
 Bohr also suggested: that the electrons don’t continuously lose
energy as they travel; they can only gain and lose energy by
jumping from one allowed orbit to the next; and atoms don’t radiate.
- This picture is of Bohr in Einstein discussing the
atomic model.
Quantum Model
The quantum model basically shows
that the atom’s electron are in orbits
(or energy levels) around the nucleus
of the atom.
How was this discovery found?!
Bohr actually used Ernest Rutherford’s
Gold Foil experiment. He then
discovered that Rutherford’s idea had
few problems.
Other Information
 In 1911 Niels Bohr followed experimental
work going on under the supervision of Sir
JJ Thomson.