Writing Formulas for Ionic Compounds

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Writing Formulas for Ionic Compounds
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• Oxidation Numbers for
• the Group A Elements

3
1
2
3-
2-
1-
0
NA
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• When you write ions, use the element symbol and
  the oxidation number written as a superscript.
• bromine
• sulfur
• cesium

called bromide in a compound
Br-1
called sulfide in a compound
S-2
Anions change end of name to ide.
Cs1
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• If you need the oxidation number for a transition
  or inner transition metal, it will be given to
  you because these elements typically have more
  than one oxidation number.
• Ox. for transition/inner transition metals will
  be in the form of a Roman Numeral!
• Exceptions
• Pb and Sn use Roman numerals even
  though they are NOT transition metals
• Ag and Zn do NOT use Roman
  Numerals even though they ARE transition
  metals

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• example
• nickel (II) chloride (NiCl2)

The (II) belongs to nickel
which means nickel has a 2 charge while chlorine
has a -1 charge!
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What is the oxidation number for the metal in
each compound?
Pb4

• Lead (IV) oxide
• Scandium (II) nitride

Sc2
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Monatomic Ions

• A monatomic ion is an ion made up of one element.
• examples H1 O-2 F-1 Ba2
• Monatomic ions bond to make a binary compound.
• Binary compounds are made of a monatomic cation
  and a monatomic anion.

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To Write Formulas with Monatomic Ions, use the
criss-cross method!
bromine name changed to bromide in a compound

• Write the formula for barium bromide.
• First Write each element symbol and oxidation
  number.
• Always write the positive ion first!!!
• Next Criss-cross the oxidation numbers. Swap
  the ox. s and write them as SUBSCRIPTS (lose
  the and signs)

Ba2 Br-1
Ba2 Br-1
Ba1Br
1

BaBr2
2
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Write the formulas for

• Iron (III) chloride
• Sodium oxide
• Magnesium nitride

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Polyatomic Ions

• A polyatomic ion is an ion made up of more than
  one element.
• These are on the back of your periodic table!
• The entire polyatomic ion has an oxidation number
  (NOT the individual elements).

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Polyatomic Ions

• Example PO4-3 is the polyatomic ion phosphate
  with an oxidation number of -3.
• Example SO3-2 is the polyatomic ion sulfite
  with an oxidation number of -2.
• Most polyatomic ions end in the suffix ate or
  ite.

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To write formulas with polyatomic ions

• First Write each element and polyatomic ion
  symbol and oxidation number.
• Always write the positive ion first!!!
• Next Place polyatomic ion in PARANTHESES
• Finally criss cross the oxidation numbers
• NEVER, NEVER, NEVER, EVER CHANGE THE SUBSCRIPT
  WITHIN THE POLYATOMIC ION ITSELF!

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• Write formulas for
• Calcium Phosphate
• Magnesium Nitrate

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• ONE LAST NOTE Chemical formulas must be in the
  lowest, reduced form!!!
• Write formulas for
• lead (II) oxide
• calcium sulfide

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Lets Try More!
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Nomenclature of Ionic Compounds

• Nomenclature means naming.
• Naming Ionic Compounds with Monatomic Ions
• First Name the cation (positive ion) DO NOT
  CHANGE THE CATIONS NAME IN ANY WAY and write it
  down.
• Note If the cation is a transition or inner
  transition metal, you must indicate its charge
  (the oxidation number) using Roman numerals in
  parentheses after the metals name.
• Ex iron (II) chloride its chemical formula is

FeCl2
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• Ex What would these anions be named in a
  compound?
• Oxygen ______________
• Sulfur ______________
• Nitrogen ______________
• Iodine ______________
• Phosphorus ______________
• Chlorine ______________

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Name These

• Ex NaCl ____________________
• Pb3P2 ___________________

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Naming Ionic Compounds with Polyatomic Ions

• First Name the cation ion first (NEVER CHANGE
  THE CATIONS NAME).
• Note If the cation is a transition or inner
  transition metal, you must indicate its charge
  using Roman Numerals in parentheses after the
  metals name. Ex iron (II) hydroxide (its
  chemical formula is Fe(OH)2)
• Next Name the polyatomic ion ON THE BACK OF
  THE PT (NEVER CHANGE THE POLYATOMICS NAME).
• HINT Polyatomic ions usually end in ate or
  ite!

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Try These

• Li2SO4
• (NH4)2O

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• I will do the rest with you on the board!