The Periodic Table

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The Periodic Table
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Development of the Periodic Table

• 1829 Dobereiners Triads classified elements
  into groups of 3 based on similar chemical
  properties
• 1869 Mendeleev published his table of elements
  based on increasing atomic mass.
• Came up with idea called periodicity (tendency
  to recur at regular intervals).

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The Modern Periodic Table

• Ordered based on atomic number and NOT mass.
• Periodic Law physical chemical properties of
  elements repeat in a regular pattern when they
  are arranged in order of increasing atomic number.

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Using the Periodic Table

• Modern PT is arranged according to atomic number.
• Remember that Atomic Electrons, therefore
  they are also lined up according to the of
  electrons they have.

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• Why does the 1st period have only 2 elements?
• Because only 2 electrons can occupy the 1st
  energy level in an atom.
• What happens when an element has more than 2
  electrons?
• They occupy the next energy level.

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• How many electrons can occupy the 2nd energy
  level?
• 8
• Lets go back and look again at the periodic table

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• What happens when the maximum number of electrons
  (8) occupy the outermost energy level?
• They are unreactive
• These elements are unreactive.

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• Because elements in the same group have the same
  of valence electrons, they have similar
  properties.

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Groups 1 2 Group Valence
electronsGroups 13-18 2nd digit in group
valence electrons
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• Because elements in the same group have the same
  of valence electrons, they have similar
  properties.
• Because the PT relates group period numbers to
  valence electrons, its useful to predict atomic
  structure, and therefore chemical properties.

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Classifying Elements

• Elements are classified as metals, nonmetals, and
  metalloids
• Majority of elements are metals

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Metals

• Have strength durability
• Have luster, conduct heat electricity
• Usually bend without breaking
• With the exception of tin, lead, bismuth, they
  have 1, 2 or 3 valence electrons
• All except mercury are solids at room temp
• Most have extremely high melting points
• Most are not main group elements
• Most located in groups 3-12 and are called
  TRANSITION ELEMENTS
• Chemistry of transition elements is unpredictable

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Metals continued

• Inner transition elements are the Lanthanides and
  Actinides
• Lanthanides make up less than 0.01 of the Earth
  so they are called RARE EARTH metals
• Actinides are radioactive and none beyond 92
  occur in nature
• Chemistry of Rare Earth metals is unpredictable
  because of their complex atomic structures

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Nonmetals

• Many nonmetals are abundant in nature
• Most do not conduct electricity
• Are poorer conductors of heat than metals
• Are brittle when solid
• Many are gases at RT
• Those that are solids lack the luster of metals
• MP tend to be lower than those of metals
• With the exception of carbon, have 5, 6, 7, or 8
  valence electrons

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Properties of Metals Nonmetals

• Bright metallic luster
• Solids are easily deformed
• Good conductors of heat electricity
• Loosely held valence electrons

• Non-lustrous, various colors
• Solids may be hard or soft, usually brittle
• Poor conductors of heat electricity
• Tightly held valence electrons

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Metalloids

• Have some chemical physical properties of
  metals other properties of nonmetals
• Best known is silicon
• A semiconductor is an element that does not
  conduct electricity as well as a metal, but does
  conduct slightly better than a nonmetal.
• The ability of a semiconductor to conduct
  electricity can be increased by adding a small
  amount of other elements
• How is silcon used in todays society?

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Semiconductors
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Different types of semiconductors
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Doping

• Addition of a small amount of another element to
  a crystal of a semiconductor
• If phosphorus is added, its 5 valence electrons
  are free to move throughout the crystal to form
  an electric current. This creates a n-type
  semiconductor
• If boron is added, its 3 electrons creates
  holes where the electrons in silicon can go to
  produce an electric current.

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Diodes

• Many semiconductor devices are made by combining
  n- and p- type semiconductors to form a diode
• This permits electrical current to flow in only 1
  direction, from the negative terminal to the
  positive terminal
• Transistors are the key components in electrical
  circuits in computers, calculators, hearing aids,
  and TVs. They are used to amplify (increase)
  electrical signals.
• Transistors, diodes other semiconductor devices
  are incorporated into thin slices of silicon to
  form integrated circuits

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Integrated Circuit