Chemical Names and Formulas

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Chapter 6

• Chemical Names and Formulas

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Intro to Chemical Bonding

• Molecules and Molecular Compounds
• In nature, only the noble gas elements, tend to
  exist as isolated, single atoms (monatomic).
• A molecule is the smallest electrically neutral
  unit of a substance that still has the properties
  of that substance.
• Oxygen is an example of a diatomic molecule O2
• Ozone is an example of a triatomic molecule O3

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Intro to Chemical Bonding (cont)

• Ions and Ionic Compounds
• Ions are atoms or groups of atoms that have a
  positive or negative charge
• An ion forms when an atom or group of atoms gains
  or loses an electron.
• A cation is any atom or group of atoms that has a
  positive charge.
• Metallic
• Symbol -
• An anion is any atom or group of atoms that have
  a negative charge.
• Nonmetallic
• Symbol
• Name change to end in -ide

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Intro to Chemical Bonding (cont)

• Ionic compounds are compounds composed of anions
  and cations.
• Usually composed of metal cations and nonmetal
  anions
• Are electrically neutral
• The total positive charge of the cations equals
  the total negative charge of the anions.
• See table 6.1 p. 137

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Representing Chemical Compounds

• Chemical Formulas
• Shows the kinds and numbers of atoms in the
  smallest representative unit of the substance
• See figure 6.5 for diatomic molecules
• Molecular Formulas
• Shows the kinds and numbers of atoms present in a
  molecule of a compound
• See figure 6.7 and 6.8 for formulas and models

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Representing Chemical Compounds (cont)

• Formula Units
• The lowest whole-number ratio of ions in an ionic
  compound
• Ionic compounds exist as collections of
  positively and negatively charged ions arranged
  in repeating three dimensional patterns (NOT
  molecules)
• The Law of Definite Proportions
• In samples of any chemical compound, the masses
  of the elements are always in the same
  proportions
• The Law of Multiple Proportions
• Whenever 2 elements form more than 1 compound,
  the different masses of one element that combine
  with the same mass of the other element are in
  the ratio of small whole numbers

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Ionic Charges

• Monatomic Ions
• The ionic charges can often be determined by
  using the periodic table
• The metals in Group 1A, 2A, 3A, lose electrons
  when they form cations. Thus the ionic charge is
  positive and is numerically equal to the group
  number.
• See table 6.2 p. 143
• Many of the cations of transition metals have
  more than one common ionic charge.
• See table 6.3 p. 144 for naming of ions w/ more
  than one ionic charge

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Ionic Charges (cont)

• Polyatomic Ions
• Are tightly bound groups of atoms that behave as
  a unit and carry a charge
• See table 6.4 p. 147
• Most polyatomic ions end in ite or ate
• The ite ending indicates one less oxygen atom
  that the ate ending
• 3 exceptions
• The positively charged ammonium cation (NH4)
• 2 that end in ide cyanide ion (CN-) and the
  hydroxide ion (OH-)

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Ionic Compounds

• Writing Formulas for Binary Ionic Compounds
• Compounds composed of two elements
• The positive charge of the cation must balance
  the negative charge of the anion the net charge
  must be zero
• Crisscross method
• Fe3 O2-
• Fe2O3

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Ionic Compounds (cont)

• Naming Binary Ionic Compounds
• Write the name of the metal (cation) followed by
  the nonmetal (anion), then add the ending ide
• CaS Calcium sulfide
• For ions with more than one charge, you must
  specify which ion is in the compound with a roman
  numeral
• Cu2 O2- CuO copper(II) oxide

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Ionic Compounds (cont)

• Ternary Ionic Compounds
• A compound that contains atoms of three different
  elements
• Usually they contain a polyatomic ion
• First write the symbol and charge for each ion
  and balance the charges using the crisscross
  method.
• When more than 1 polyatomic ion is needed to
  balance the charges, parentheses are used to set
  off the polyatomic ion.
• Name the cation first, then the anion.

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Molecular Compounds and Acids

• Binary Molecular Compounds
• Composed of 2 nonmetallic elements
• See table 6.5 p. 159 for naming
• The prefixes tell how many atoms of each element
  are present in each molecule.
• If there is a single atom of the first element,
  drop the mono-.
• The vowel at the end of the prefix is dropped if
  the element starts with a vowel.
• The names of all binary molecular compounds end
  in ide.

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Molecular Compounds and Acids (cont)

• Naming Common Acids
• Acids are compounds that produce hydrogen ions
  when dissolved in water.
• When naming acids and writing formulas, you can
  consider them to be combinations of anions with
  as many hydrogen ions (H) as are needed to make
  the molecule electrically neutral.
• Copy the names and formulas on p. 160

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Summary of Naming and Formula Writing

• See figure 6.21 p. 161
• Rules
• In an ionic compound, the net ionic charge is
  zero.
• An ide ending generally indicates a binary
  compound.
• An ite or ate ending means there is a
  polyatomic ion that includes oxygen in the
  formula
• Prefixes in a name generally indicate that the
  compound is molecular. They show the of each
  atom present in the compound.
• A Roman numeral after the name of a cation shows
  the ionic charge of the cation.
• See figure 6.23 p. 162