Why We Use What We Do

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Why We Use What We Do

• Periodic Table, Atomic Number Isotopes

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The Periodic Table

• Mid 1800s
• 60 Different Elements were identified
• 5 were gases at room temperature (all non-metals)
• H, O, N, F, Cl
• 2 were liquids
• Hg (metal)
• Br (non-metal)
• The rest were solids

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The Periodic Table

• Construction of The Periodic Table
• Elements with similar properties were placed near
  one another.
• Dimitri Mendeleev
• In 1869 he published a periodic table

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Mendeleevs Periodic Table
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The Periodic Table

• Mendeleevs Table arranged by
• Atomic Weight (Molar Mass)
• Combining Capacity
• Chemical Properties
• NaCl vs CuCl2
• Modern Periodic Table arranged by
• Atomic Number
• Number of valence electrons
• Supports Combining Capacity Properties

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The Periodic Table

• Atomic Number
• Determined by the number of Protons in the
  nucleus
• Positive Particles (p)
• Each element has its own atomic number
• Na 11 protons (p)
• Identify every atoms as a particular element by
  this number.

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Molar Mass
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The Periodic Table

• Mass Number
• Mass (p) (n0)
• Does not include (e-)
• (e-) too small to contribute to the overall mass
  of the atom.
• Mass number changes when the number of neutrons
  change.

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The Periodic Table

• Isotopes
• Atoms with the same number of (p) but a
  different number of (n0).
• Atoms of the same element with different mass s
• 14C Radioactive
• 12C Non-radioactive
• For Example Hydrogen (H with one (p) but no (n0)
  ) and Deuterium (H with one (p) and one (n0) ).
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The Periodic Table

• Why use Atomic Number rather than Molar Mass
  (atomic weight)?
• Organization by Molar Mass (atomic weight) works
  well for small atomic weights but not large ones.
• Due to many varieties of isotopes

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The Periodic Table

• Vertical arrangement
• Elements with similar properties were placed in
  vertical Groups (columns) or Families.

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Group
Molar Mass
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Molar Mass
Group
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Molar Mass
Group
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Molar Mass
Group
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Molar Mass
Group
Etc.
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The Periodic Table

• Horizontal arrangement
• Placed by increasing atomic weights in rows
  called Periods.

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Molar Mass
Periods
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Periods
Molar Mass
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Periods
Molar Mass
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Molar Mass
Periods
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Molar Mass
Periods
Etc.
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Families/Groups

• Alkali Metals
• Group 1 Lithium, Sodium, Potassium, Rubidium,
  Cesium, Francium
• 1 electron in valence (outer) shell
• Very, VERY reactive not found free in nature
• Alkali Metal Clip

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Family/Group

• Alkaline Earth Metals
• Group 2 Beryllium, Magnesium, Calcium,
  Strontium, Barium, Radium
• 2 electron in valence shell
• Very reactive not usually found pure in nature

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Families/Groups

• Nobel Gases
• Group 18 Helium, Neon, Argon, Krypton, Xenon,
  Radon
• Full valence electron shell
• Very stable (not reactive)
• Under normal conditions do not form compounds
  with other elements
• XeF4 (xenon tetrafluoride) is the first reported
  stable compound of a noble gas - 1962

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Families/Groups

• Halogens
• Group 17 Fluorine, Chlorine, Bromine, Iodine,
  Astatine
• 7 electrons in valence shell
• Halogen means salt former
• Compounds they form are called salts

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Families/Groups

• Transition Metals
• Groups 3 to 12, periods 4 to 7
• 1, 2, or 3 electrons in valence electron shell
• Hard and have a high melting point
• Often used to form alloys (mixtures of metals)

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