Chp 19'2

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Chp 19.2

• Chemical Formulas

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Oxidation Numbers

• An oxidation number indicates how many electrons
  are lost or gained during the bonding process.
• Mg loses 2 electrons so it
• has an oxidation number
• of 2
• Oxygen gains 2 electrons
• so it has an oxidation
• number of 2.

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• The periodic table show the common oxidation
  numbers for groups on the periodic table.

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Element with variable oxidation numbers

• Some elements have variable oxidation
• numbers.
• In that case roman
• numbers are used to distinguish the oxidation
  numbers.

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Writing chemical formulas

• All compounds have an electrical charge of zero
  that is, they are neutral.
• Write the symbol for the positive ion first
• Write the symbol for the negative ion second.
• Add subscripts so that the sum of the positive
  and negative oxidation numbers equals zero.

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Polyatomics Ions

• Some molecules contain compound groups. These
  groups are called polyatomic ions

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Using Polyatomics

• How would you write the chemical formula for
  Calcium with Hydroxide.
• Ca is located in Group 2 so it
• has a 2 oxidation number
• OH is a polyatomic ion with a charge of 1
• In order to make the total charge 0 you need
• (Ca2) x (1) 2
• (OH-) x (2) -2
• 0

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Naming Formulas

• Write the name for the first element in the
  compound.
• Write the root name of the second element.
• Add the ending ide to the root name
• Naming BaF2
• First element is Barium
• Second element is Fluorine (root is fluor)
• The name is Barium Fluoride

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Naming Polyatomic Ions

• For polyatomic ions (use chart)
• Write the name for the first positive ion.
• Write the name for the negative ion
• Naming MgCO3
• Positive ion is Magnesium
• Negative ion is Carbonate (see chart)
• The name is Magnesium Carbonate