Electrons Electrons Electrons

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ElectronsElectronsElectrons
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Electron Configuration Just a bunch of
circles.? Not quite!
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Electron Arrangement

• The electrons that surround the nucleus of an
  atom are arranged in shells .
• Each shell has a maximum number of electrons that
  can exist
  in that shell.

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• Up to 2 electrons can exist in the first shell
• Up to 8 electrons can exist in the second and
  third shell
• Up to 18 electrons can exist in the fourth and
  fifth shell

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2
8
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Basic Atom
Electron
Nucleus
Shell or Orbit
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Beryllium Atom
Electrons
Protons
Neutrons
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Boron Atom
Electrons
Protons
Neutrons
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Carbon Atom
Electrons
Protons
Neutrons
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Nitrogen Atom
Electrons
Protons
Neutrons
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Oxygen Atom
Electrons
Protons
Neutrons
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Fluorine Atom
Electrons
Protons
Neutrons
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Neon Atom
Electrons
Protons
Neutrons
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Sodium Atom
Electrons
Protons
Neutrons
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Drawing electron dot diagrams

• We can draw diagrams to show the arrangement of
  the electrons in each element. This is called an
  electron dot diagram
• Note the example below (the symbol is put in the
  middle and the electrons around in shells)

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Electron Configurations

• The arrangement of the electrons in the electron
  shells can be written as an electron
  configuration.
• Looking at the sodium atom below, there are 2
  electrons in the first shell, 8 electrons in the
  second shell, and 1 electron in the third shell.
• This can be written as
• 2, 8, 1

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Fact 1 Elements in the same group have the same
number of electrons in the outer shell (this
correspond to their group number)
H H He
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
K Ca Fe Ni Cu Zn Br Kr
Ag I Xe
Pt Au Hg

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Fact 2 As you move down through the periods an
extra electron shell is added.
H H He
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
K Ca Fe Ni Cu Zn Br Kr
Ag I Xe
Pt Au Hg

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Fact 3 (Most important) All of the elements in
the same group have similar properties.
H He
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
K Ca Fe Ni Cu Zn Br Kr
Ag I Xe
Pt Au Hg