4.2 Names and Formulas of Compounds

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4.2 Names and Formulas of Compounds
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Chemical Names

• All ionic compounds are composed of positive and
  negative ions
• The chemical name indicates which elements are
  present in the compound
• Each name has two parts
• One for the positive ion
• One for the negative ion

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Chemical Names

• To Name an Ionic Compound
• Name the positive ion
• - its the same as on the periodic table
• Name the negative ion
• -drop the end of the element name and add ide

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Examples

• NaCl
• KBr
• CaF2
• 4. MgO

Sodium chloride
Potassium bromide
Calcium fluoride
Magnesium oxide
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Chemical Formulas

• Symbols represent the elements in the compound
• Subscript numbers following the symbol show how
  many of each element are present.
• Example
• Sr3P2
• - Contains 3 atoms Sr (strontium) and 2 atoms P
  (phosphorus)

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Chemical Formulas

• The ion charge shows what ion each element forms
  to complete their valence shell of electrons
• Al has an ion charge of 3, therefore it loses 3
  electrons
• Br has an ion charge of -1, therefore it gains
  one electron
• For Al and Br to form a compound Al needs to give
  away 3 electrons and Br needs to accept them.
• But wait!!! Br only needs to accept one, so how
  does this work??

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• Complete the Chemical Formulas worksheet to
  help you figure out how to determine the chemical
  formula for an ionic compound.

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Chemical Formulas

• Each Br can accept only 1 electron, so 3 Br atoms
  are needed to combine with 1 Al
• The overall formula needs to show this ? AlBr3

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Chemical Formulas

• What would the Ionic Formula be for a compound
  made of Aluminum and Sulphur?
• Al has an ion charge of 3
• S has an ion charge of -2

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• For all elements to end up with full valence
  shells, 2 atoms of Al and 3 of S are required.
• Formula Al2S3

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Shortcut to write the formula

1. Write the symbol and ion charge of the positive
   ion
2. Write the symbol and ion charge of the negative
   ion
3. Criss-cross the charges and write as subscripts
4. Reduce numbers (if possible)

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Examples

• Aluminum sulphide
• Al3 S-2
• Al S
• Al2S3

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Examples

• Magnesium Oxide
• Mg2 O-2
• Mg O

Mg2O2
REDUCE!!
MgO
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Assignment

• Complete the practice problems on pages 86 and 87

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Compounds Containing a Multivalent Metal

• Multivalent metals have more than one possible
  ion charge.
• The name must indicate which ion charge is used
  in the formation of the compound
• We use roman numerals to indicate ion charge

I 1 VI 6 II 2 VII 7 III
3 VIII 8 IV 4 IX 9 V 5 X 10
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Compounds Containing a Multivalent Metal

• Examples
• V4 Vanadium (IV)
• Ni3 Nickel (III)
• Writing formulas is identical to other ionic
  compounds, simply use the roman numeral to
  determine the ion charge of the cation!

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Compounds Containing a Multivalent Metal

• Example
• Manganese (IV) sulfide
• Mn4 S2-
• Mn2S4
• MnS2
• Complete the practice problems on page 89

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Compounds Containing a Multivalent Metal

• Naming these types of compounds requires an extra
  step.you must UNCRISSCROSS!!

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Compounds Containing a Multivalent Metal

• Example Name PdS2
• 1. Look up the metal on the periodic table and
  confirm that it is multivalent.
• 2. Uncrisscross so that the subscripts become
  charges once again

Pd1S2
Pd2 S1-
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Compounds Containing a Multivalent Metal

• Check the ion charge of the non-metal to make
  sure its correct. If not, multiply both charges
  to make it correct.
• Pd2 S1-
• - wait!! Sulfur should have an ion charge of
  -2!!
• -to fix this, multiply both ion charges by 2
• Pd4 S2-

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Compounds Containing a Multivalent Metal

• Name the metal, using roman numerals to indicate
  its ion charge
• Palladium (IV)
• Name the non-metal, swapping ending for ide.
• Palladium (IV) Sulphide

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Compounds Containing a Multivalent Metal

• Name these compounds
• SnCl2
• PbS2
• Complete the practice problems on page 90!

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Polyatomic Ions

• Some special molecules lose or gain electrons as
  a group
• These ionic molecules are called polyatomic ions

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Polyatomic Ions

• You can recognize that a compound has a
  polyatomic ion in it because it will be made up
  of MORE THAN 2 TYPES OF ATOMS!
• Naming
• Example NaNO3
• Name the cation
• Sodium
• 2. Name the polyatomic ion
• Nitrate
• Sodium Nitrate

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• Writing Formulas
• Write the symbol and ion charge for both parts of
  the name
• Criss Cross the charges
• - put brackets around the polyatomic ion if
  necessary
• 3. Reduce if possible
• Example Calcium Bicarbonate
• Ca2 HCO3-

Ca HCO3
Ca(HCO3)2
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Complete the practice problems on page
91Complete Check Your Understanding page 95 1-6