Binary compounds

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Binary compounds

• Chapter 6 part I

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Chemical Formulas

• Chemical formulas inform as to the type of
  elements that make up the compound and in what
  ratios.
• Chemical formulas describe both ionic compounds
  and molecules.

• Example
• H2O 2 hydrogens for every 1 oxygen
• This is a molecule.
• CaCl2 2 chlorines for each calcium.
• This is an ionic compound.

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Molecular formulas

• Molecular formulas have 2 nonmetals bound
  together.
• Molecules are held together by sharing electrons,
  not by charge.
• Hydrogen is a nonmetal!!

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Formula Units

• Chemical formulas for ionic compounds are called
  formula units.
• Each unit is part of a larger structure.
• Consist of a metal and a nonmetal.
• They are held together by charge.

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Ions and valence electrons

• To write chemical formulas one needs to
  understand how these elements combine.
• Electrons are the key!
• Valence electrons (outer shell electrons) may be
  determined by the group on the periodic table.

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Lewis dot

• The number of valence electrons is represented by
  dots outside the atomic symbol.
• Hydrogen has one valence electron and therefore
  one dot.
• Lithium has one valence electron and therefore
  one dot
• Berylium would have two dots and so on.
• These are the same numbers as found in the
  representative elements.

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Lewis Dot

• Practice Lewis Dot on your worksheet.
• What happens to the number of dots if the element
  forms an ion?

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Ionic compounds and Lewis Dot

• When Ions lose an electron they have a complete
  shell, but they have a charge.
• These charged ions are attracted to the opposite
  charge forming salts.

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Molecular Bonding and Lewis Dot

• Except for H and He, how many electrons do the
  elements in a molecule want around them?
• s2p6 8 electrons to mimic the noble gases.
• This is called the octet rule. Octet8

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Bonding and Lewis Dot

• Double bonds and single bonds are also
  represented by Lewis dot.
• Try bonding on your worksheet.