The Periodic Table

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The Periodic Table

• 1868
• Was organized according to the properties of the
  known elements
• Dmitri Mendeleev noticed that when the elements
  were put into order by their atomic mass, some
  of their properties repeated periodically

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Dmitri Mendeleev

• Noticed that properties repeat, e.g. melting
  point, react with oxygen, density, mass

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Periodic Table

• So he put them in columns with others that are
  similar.
• Didnt know anything about protons, electrons,
  etc. Just made observations!
• Even made some guesses about ones that were
  missing and their properties. He was correct!

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Guesses

• Eka-Aluminum
• Atomic Mass 68, density 5.9
• Gallium (Ga)
• Atomic mass 69.7, density 5.94
• Eka-Silicon
• Atomic Mass 72, density 5.5
• Germanium (Ge)
• Atomic Mass 72.6, density 5.7

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Atomic Theory

• Democritus 5th century
• BCE
• Matter is made up of atoms
• Atoms are solid
• No internal structure
• Different sizes
• Space in between them (void)

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Atomic Theory

• John Dalton 1800s
• Father of modern atomic theory
• Discovered atomic weights and symbols for
  elements
• elements made of atoms
• atoms of an element same mass
• different elements have different masses
• Atoms combine in small, ratios such as 11, 12,
  23
• atoms cant be created or destroyed

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Atomic Theory

• JJ Thompson 1897
• Discovered electron (first subatomic particle)
• Believed atoms had negative charges floating in
  a sea of positive ones, like chocolate chips in
  a cookie
• Called plum pudding
• model

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Atomic Theory

• Earnest Rutherford 1911
• Discovered nucleus of atom and said it was
  positive
• Electrons orbit through empty space around
  positive nucleus

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Atomic Theory

• Niels Bohr 1914
• Discovered energy levels for electrons
• Farther away from nucleus, higher energy level
• Planetary model like planets orbiting sun

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Atomic Theory

• Quantum theory
• Current theory
• Electrons dont have orbits like planets
• They move to fast to know exactly where they
  are, but we can tell where they probably are
• Electron cloud is place where they probably are

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Electron cloud

• Broken down into energy levels
• Energy levels have sublevels called orbitals
• Energy levels and orbitals only hold a certain
  number of electrons maximum
• Called s p d f

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