Molecular Compounds: Formulas

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Molecular Compounds Formulas Naming

• Ch 6.3b - Covalent Bonds

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What type of bond?

• Covalent
• Electrons are shared between atoms
• Forms between non-metals
• Covalent Bonds ? Molecular Compounds
• Which elements are non-metals?

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Describing Molecular Compounds

• What information do the name and formula of a
  molecular compound provide?
• Ionic Bonds (Ionic Compounds) -
• The name distinguishes the compound from other
  ionic compounds containing the same elements.
• The formula of an ionic compound describes the
  ratio of the ions in the compound.

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Describing Molecular Compounds

• Covalent Bonds (Molecular Compounds)
• The name and formula of a molecular compound
  describe the type and number of atoms in a
  molecule of the compound.

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Naming Molecular Compounds

• Naming Order
• Step 1 Element that is farthest to the left side
  of the periodic table is typically named 1st.
  (left to right)
• The most metallic element appears first in the
  name. These elements are farther to the left in
  the periodic table.
• If both elements are in the same group, the more
  metallic element is closer to the bottom of the
  group.
• Formulas are written same way
• Example
• Sulfur is named before chlorine ? SCl2

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Naming Molecular Compounds

• Exception Oxygen Halogens
• Oxygen comes 2nd when combined with
  lower-electronegativity halogens (Group 17)
• Example ClO2 (electronegativity Cl 3.0 O
  3.5)
• Step 2 Second element name is changed to end in
  ide (like the anion in an ionic compound)
• Examples
• Chlorine becomes chloride
• Oxygen becomes oxide

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Naming Molecular Compounds

• There may be more than one molecular compound
  that can exist with the same two elements.
• Greek prefixes are used to name molecular
  compounds.
• Step 3 Add prefixes to elements names to specify
  the number of atoms of each element in the
  compound.

• mono - one
• di - two
• tri - three
• tetra - four
• penta - five

• hexa - six
• hepta - seven
• octa - eight
• nona - nine
• deca - ten

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Naming Molecular Compounds

• Example
• Both Compounds contain Nitrogen and Oxygen
• N2O ?
• Dinitrogen monoxide
• N4O5 ?
• Tetranitrogen pentoxide

• Prefixes
• mono - one
• di - two
• tri - three
• tetra - four
• penta - five

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Naming Molecular Compounds

• Exception to Step 3 No prefix is used if there
  is only one atom of the 1st element in the
  compound.

• CO ? Carbon monoxide
• CO2 ? Carbon dioxide
• SO10 ? Sulfur decaoxide

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Naming Molecular CompoundsMore Examples

• N2Cl5 ?
• Dinitrogen pentachloride
• N2O5 ?
• Dinitrogen pentoxide

• P5Cl6 ?
• Pentaphosphorous hexachloride
• SO10 ?
• Sulfur decaoxide

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Writing Molecular Formulas

• Step 1 Write the symbols for the elements in the
  order the elements appear in the name.
• Step 2 Write the numerical value of the prefixes
  as subscripts for the corresponding element in
  the formulas.
• The prefixes indicate the number of atoms of each
  element in the molecule.
• If there is no prefix for an element in the name,
  there is only one atom of that element in the
  molecule.

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Writing Molecular Formulas

• Examples
• Diphosphorus Pentoxide ? P2O5
• Silcon Dioxide ? SiO2
• Carbon Tetrachloride ? CCl4
• Trineptunium Octoxide ? Np3O8

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You Try

• Give the formula for
• Oxygen Difluoride ?
• Phosphorus Tribromide ?
• Trisilicon Tetranitride ?
• Give the Name for
• NO2 ?
• N2O3 ?
• SO3 ?

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You Try - Answers

• Give the formula for
• Oxygen Difluoride ? OF2
• Phosphorus Tribromide ? PBr3
• Trisilicon Tetranitride ? Si3N4
• Give the Name for
• NO2 ? Nitrogen Dioxide
• N2O3 ? Dinitrogen Trioxide
• SO3 ? Sulfur Trioxide