Atomic Theory

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Atomic Theory
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Atomic Theory

• John Dalton and His Atomic Theory
• In 1803, John Dalton (17661844) forcefully
  revived the idea of atoms. Dalton linked the
  existence of elements, which cannot be decomposed
  chemically, to the idea of atoms, which are
  indivisible.

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John Daltons Theory

• Compounds, which can be broken down into two or
  more new substances, must contain two or more
  different kinds of atoms. Dalton went further to
  say that each kind of atom must have its own
  properties,including mass.This idea allowed his
  theory to account quantitatively for the masses
  of different elements that combine chemically to
  form compounds.

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Daltons Theory

• 1. All matter is composed of tiny indivisible
  particles called atoms.
• 2. Atoms of the same element are identical. The
  atoms of any one element are different from those
  of any other element.

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Daltons Theory

• 3. Atoms of different elements can combine with
  one another in simple whole number ratios to form
  compounds.
• e.g. H2O CO2 HCl
• 4. Chemical reactions occur when atoms are
  separated, joined or rearranged. Atoms of one
  element are not changed into atoms of another by
  a chemical reaction.

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Electrons

• Electrons are subatomic particles found rotating
  around the nucleus of every atom.The number of
  electrons outside the nucleus is always the same
  as the number of protons in the nucleus. This
  makes the atom electrically neutral.

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Arrangement

• The electrons which move around the nucleus of an
  atom have different quantities of energy. Those
  restricted to being closest to the nucleus have
  the least energy while those with the ability to
  be furthest away from the nucleus have the most
  energy.

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Electron Arrangement

• The electrons can therefore be regarded as
  occupying different spherical volumes of
  different sizes, these levels usually being
  referred to as shells.It is worth noting that
  within each shell the electrons are not orbiting
  the nucleus at a fixed distance but can travel
  anywhere within the spherical shape of that
  shell.

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Protons

• Protons are stable subatomic particles found in
  the nucleus of every atom.
• The number of protons in the nucleus is the
  proton number of that atom, which tells which
  element the atom belongs to.
• The proton number determines the relative
  position of the element on the periodic table.

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Proton Discovery

• Two scientists, W. Wien in 1898, and J.J.Thomson
  in 1910, concluded that a positive particle
  existed and had a mass equal to that of a
  hydrogen atom.
• In 1919, E.Rutherford demonstrated that particles
  were emitted when nitrogen was bombarded with
  alpha particles. In 1920 he proposed that these
  hydrogen nuclei were fundamental particles and he
  named them PROTONS.

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Neutrons

• Neutrons are subatomic particles found in the
  nucleus of every atom.The number of neutrons in
  the nucleus does not follow a regular pattern.The
  number of neutrons can vary even for atoms of the
  same element.(Isotope)
• Neutrons have no charge.

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Neutrons

• Discovery
• Neutrons were the last of the three main
  subatomic particles to be discovered, being first
  recorded in 1932.

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Concept Map
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Imagine This!

• If an atom were the size of a football stadium,
  the nucleus would be the size of a marble!
• If people were the size of atoms, all the people
  living on the earth today would fit on the head
  of a pin!f