Formulas and Nomenclature

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Formulas and Nomenclature
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Basic Rules For Writing Formulas

• Sum of the charges MUST equal 0 in a neutral
  compound. (in a polyatomic ion it equals the ions
  charge)
• H20
• Positive ion is written first, followed by
  negative ion
• Na Cl- NaCl
• When more than 1 of the same element is in the
  compound, a subscript is written after the
  element (no paranthesis)
• H20

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• When more than 1 polyatomic ion is in a compound,
  the ion is enclosed in a parenthesis and the
  subscript follows
• Mg2 NO3- Mg(NO3)2
• Ion a charged atom
• Oxidation number ions charge
• Monatomic ion ion with only one atom
• Polyatomic ion ion with more than one atom

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• Oxidation number for a free element is zero
  (normal atom)
• There are 7 diatomic elements that occur as pairs
  when in a pure state O2, N2, I2, H2, F2, Cl2, Br2
• The oxidation for Hydrogen is usually 1 except
  in hydrides (group 1 and 2)
• The oxdation of Oxygen is -2 except as a
  peroxide (with group 1 2)

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Type 1 Binary Ionic Compounds

• Binary ionic compounds contain a positive ion
  (cation)which is always written first in the
  formula and followed by a negative ion (anion).
• (The Type 1 metal present forms only a single
  cation. This means the metals only has one
  charge or oxidation state.)

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Writing Binary Ionic Formulas

• Writing Binary Ionic Formulas is very simple. If
  the oxidation numbers or charges of the ions do
  not balance each other out, we criss-cross.
• Example Na S2- (these do not balance!)
• Na S2- Na2S
• (when the charges balance, the formula is
  complete)
• Make sure you simplify the subscripts. It is a
  ratio that is based on the Lowest common mulitple

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Type 1 Binary Ionic

• Nomenclature Rules for naming binary ionic
  formulas
• 1st elements always says its complete name
• 2nd element drops ending (uses only the root
  word) and adds an ide ending
• Example KCl Potassium chloride

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• Hydrides and peroxides form compounds with group
  1 and 2 elememts
• Ex
• MgH2 and NaH

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Type IIBinary Ionic Compounds

• Type II binary ionic compounds contain metals
  that have more than one type of cation.
• Systematic or stock system
• Example Fe 2 and Fe3
• Both ions are iron but with different oxidation
  numbers.

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Writing formulas for Type II Binary Ionic
Compounds

• These formulas are written exactly like Type I
  formulas. If the oxidation numbers do not
  balance out, you criss-cross the charges to
  form subscripts.
• Fe2 Cl- ? FeCl2

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Type II Binary Ionic Compounds

• Nomenclature Rules
• Cation says its full name
• Oxidation number is given in Roman numerals after
  the cations name
• Anion drops its ending (to the root word) and
  adds an ide ending

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Nomeclature for Type II Binary Ionic Compounds

• Examples
• FeCl2 -- Iron (II) chloride
• Cu3N2 -- Copper (II) nitride

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You dont know the charge of the cation?

• If you do not know the oxidation number of the
  cation, you can determine the charge by doing a
  little algebra. Determine the charge of the
  anion, then multiply the anions charge by the
  subscript. Take that number and divide by the
  cations subscript.
• This will determine the oxidation number of the
  cation.

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Find the charge of Carbon

• CaCO3
• You know Ca has a 2 charge and O has -2
• 1(2)X3(-2)0
• X4

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Special names for Type II Cations

• Some Type II cations have a name using the old
  system as well as the new system.
• The old system, still widely used, adds to the
  root or stem of the Latin name of the metal the
  suffixes ous and ic. These represent the lower
  and higher charges respectively.

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Old Names for Type II ions
Ion Old System New System
Fe2 Ferrous Iron (II)
Fe3 Ferric Iron (III)
Cu Cuprous Copper (I)
Cu2 Cupric Copper (II)
Sn2 Stannous Tin (II)
Sn4 Stannic Tin (IV)
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Two Polyatomic Ions with Old System Names
Ion Old System New System
NH4 Ammonium Ammonium
Hg22 Mercurous Mercury (I)
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Writing Ternary Ionic Compound Formulas

• Ternary Ionic Formulas are formed with a cation
  or an anion with two or more elements present.
  We call these anions POLYATOMIC.
• Polyatomic ions may be used with either
• Type I or Type II ions.

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Writing Formulas with Polyatiomic Ions

• Formulas are written like Type I or Type II ions.
  If the oxidation numbers or charges do not
  balance, you Criss-Cross.

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Writing Formulas with Polyatomic Ions

• Examples
• Pb2 PO43- (the charges do not balance)
• Pb2 PO43- Pb3(PO4)2
• The polyatomic ions is in parentheses whenever a
  subscript is added.

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Naming Ternary Ionic Formulas

• Nomenclature rules
• The Type I cation says its complete name, Type II
  cations give charge or use old system of naming
• The polyatomic says its complete name

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Ternary Ionic Compounds

• Examples
• PbSO4 ? lead (II) sulfate
• The charge on sulfate is a 2-, therefore the
  charge on the lead must be a 2.

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Type III Binary Covalent Formulas

• Type III compounds are nonmetalnonmetal covalent
  compounds.
• In order to form these compounds, we cannot use
  charges to predict the formula because the
  valence electrons are not transferred from one
  element to another like ionic compounds. These
  elements share.

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Binary Covalent Compounds

• In order to name the binary covalent compound, we
  must use prefixes to tell how many of each
  different element is used in the compound.
• You NEVER criss-cross charges with covalent
  compounds.

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Greek Prefixes for Covalent Compounds

• mono 1
• di 2
• tri 3
• tetra 4
• penta -- 5

• hexa 6
• hepta 7
• octa 8
• nona 9
• deca-- 10

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Binary Covalent Compounds

• Nomenclature rules for Binary Type III compounds
• The first element in compound is named first,
  using the full element name.
• The second element is named as if it were an
  anion (--ide ending)
• Prefixes are used to denote the numbers of atoms
  present.
• The Prefix mono is NEVER used for naming the
  first element.

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Naming Binary Covalent Compounds

• Example CCl4 -- Carbon tetrachloride
• 1st element is carbon
• 2nd element is chlorine (drops ine and replaces
  with ide)
• 2nd element receives prefix denoting number of
  chlorine atoms
• NOTE mono was not used with 1st element!

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Nomenclature continued

• Example N2O dinitrogen monoxide
• 1st element says its name
• 2nd element drops ending and adds ide
• Prefixes are used with both elements to denote
  quantity in molecule
• dinitrogen monoxide (prefixes are underlined
  only for emphasis)

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How do I write the formula from the name?

• In Type III compounds, writing the formula from
  the name is very simple. The prefix tells you
  exactly how many of each element is present.
• Example
• Dinitrogen pentoxide N2O5