Polyatomic Ions Writing Formulas / Naming Compounds

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Polyatomic IonsWriting Formulas / Naming
Compounds

• A polyatomic ion is a covalent molecule that has
  an ionic charge. (As opposed to being a neutral
  molecule.)
• Poly many
• Atomic atoms
• Ion charged particle
• A charged particle that consists of more than one
  atom.

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Polyatomic Ions

• Examples
• Sulfate SO4-2
• Nitrate NO3-1
• Phosphate PO4-3
• Chlorate ClO3-1
• Carbonate CO3-2
• Notice the ending has changed to ate.

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Writing Formulas

• Sodium Sulfate
• Write the formula for the metal. Add the
  oxidation number from the periodic table.
• Na1
• Write the formula for the polyatomic ion from the
  ion chart. Add its oxidation number.
• SO4-2

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Sodium SulfateNa 1 SO4-2

• Determine the common factor of the two oxidation
  numbers. In this case, 2.
• Decide how many of each ion is needed to equal
  the common factor. In this case, 2 sodium ions
  and 1 sulfate ion.
• Write these numbers as the subscript for each
  ion.
• Na2SO4

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Calcium Phosphate

• Write the formula for the metal. Add the
  oxidation number from the periodic table.
• Ca2
• Write the formula for the polyatomic ion from the
  ion chart. Add its oxidation number.
• PO4-3

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Calcium PhosphateCa 2 PO4 -3

• Determine the common factor of the two oxidation
  numbers. In this case, 6.
• Decide how many of each ion is needed to equal
  the common factor. In this case, 3 calcium ions
  and 2 phosphate ions.
• Write these numbers as the subscript for each
  ion.
• Ca3(PO4)2
• Notice that the polyatomic ion must be placed in
  parenthesis or, instead of 2 phosphate ions, you
  would have 42 Oxygen atoms and 1 Phosphorus
  atom. Ca3PO42

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Naming Compoundsw/ Polyatomic Ions

• KClO3
• Write the name of the metal.
• Potassium
• Write the name of the polyatomic ion from the ion
  chart.
• Chlorate
• Name the compound.
• Potassium Chlorate

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Mg3(SO4)2

• Name the metal.
• Magnesium
• Name the polyatomic ion from the ion chart.
• Sulfate
• Name the compound.
• Magnesium Sulfate

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Some Additional Examples

• Calcium Hydroxide
• Ca2 OH-1
• The least common factor is 2. Therefore, 1
  calcium ion will bond with 2 hydroxide ions to
  form a neutral compound.
• Ca(OH)2
• If you omitted the parenthesis, you would not
  have 2 hydroxide ions. Instead you would have 2
  hydrogen atoms and one oxygen atom. CaOH2

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Try these

• Write names for the following compounds.
• CaCO3
• Al2(SO4)3
• Ca(ClO3)2
• K3PO4
• Mg(OH)2

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Answers

• Calcium carbonate
• Aluminum sulfate
• Calcium chlorate
• Potassium phosphate
• Magnesium hydroxide

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Now, these!

• Write formulas for the following compounds.
• Lithium sulfate
• Calcium acetate
• Aluminum nitrate
• Magnesium phosphate
• Sodium carbonate

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Answers

• Li2SO4
• Ca(C2H3O2)2
• Al(NO3)3
• Mg3(PO4)2
• Na2CO3