Atomic Theory

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Atomic Theory
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Throughout history man has attempted to explain
the nature of matter.
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Democritus, an early Greek, proposed that matter
was composed of tiny indivisible particles called
atoms, meaning indivisible.
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It was not until 1807 that the atomic theory was
thoroughly revised by John Dalton.
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Daltons theory stated

• All matter is made up of tiny particles called
  atoms that cannot be split into smaller particles
  (wrong).
• Atoms cannot be created or destroyed
• All atoms of the same element have the same
  properties and atoms of different elements have
  different properties.
• Atoms of different elements can combine to form
  new substances.

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His ideas marked the beginning of the modern
atomic theory.
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The work of later scientists such as JJ Thomson,
Lord Rutherford and Neils Bohr established a
workable model of the atom.
Thomson
Rutherford
Bohr
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Dalton stated that the atom is a hard, dense
sphere.
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Thomson in 1903 stated that the atom is a mass of
positive charge and contained negative electrons.
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Rutherfords Model in 1911 described the atom as
having a dense nucleus surrounded by electrons.
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Bohr developed a model in 1913 that had a dense
nucleus and electrons that move in fixed orbits
(shells) around the nucleus in a cloud of
activity

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http//micro.magnet.fsu.edu/electromag/java/ruther
ford/http//particleadventure.org
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James Chadwick (1885 - 1962) developed a new
model of the atom in 1932. Similar in many ways
to other models, his showed the nucleus made up
of particles called neutrons.
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10,000,000 atoms placed side by side would
measure only 1 cm.
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The particles inside atoms are called subatomic
particles. In the middle of every atom is its
nucleus.
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The nucleus is made of the proton and neutron. A
third type of subatomic particle spins around the
nucleus, it is called the electron.
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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Proton
Neutron
Electron
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The electron is by far the smallest of these
subatomic particles. Their mass is only 1/1840th
the mass of a proton.
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Even though protons are much larger than
electrons, they both have the same amount of
electrical charge.
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Protons have a positive charge ().Electrons
have a negative charge (-).Neutrons have no
charge (0).
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Particles with opposite electrical charges are
attracted to each other, in the same way that
magnets with opposite poles stick together.
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Got a problem, ask a chemist, they have solutions.
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A small piece of sodium which lived in a test
tube fell in love with a bunsen burner. Oh
bunsen, my flame, I melt whenever I see you the
sodium said.Its just a phase youre going
through replied the Bunsen burner.
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Particles with the same electrical charges repel
each other, in the same way that magnets with the
same poles push apart.
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Atoms have the same number of protons as
electrons, so their electrical charges cancel
each other out, and are called neutral.
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Atoms are normally neutral and have no overall
electrical charge. This is not the case with
ions.
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Ions are charged atoms that have gained or lost
electrons. When atoms are unbalanced, it causes
them to combine or react.
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Electrons travel in shells. The first shell
contains 2 electrons, the second 8, third 8, the
fourth 18 and so on.
N
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If an atom gains an electron it becomes
negatively charged. If an atom loses an electron
it becomes positively charged.
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The number of neutrons of an atom can vary. The
different atoms caused by varying numbers of
neutrons is called an isotope.
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Different electrons can contain different amounts
of energy.
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The farther an electron is from the nucleus, the
more energy it contains.
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The number of protons an atom has determines the
type of element. If the number of protons
change, the type of atom changes.