Chapter 9: Covalent Bonds

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Chapter 9 Covalent Bonds
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What is a Covalent Bond?

• Covalent Bond -The result of sharing valence
  electrons. The shared electrons are part of the
  complete outer shell of both atoms.
• Occurs when elements are close together on the
  periodic table
• Between nonmetallic elements
• Molecule-formed when two or more atoms bond
  covalently.

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Covalent Bonds

• Can exist as gases, liquids, or solids depending
  on molecular mass or polarity
• Usually have lower MP and BP than ionic compounds
• Do not usually dissolve in water
• Do not conduct electricity

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Types of Bonds

• Nonpolar covalent (also called pure covalent)
  equal sharing of electrons between atoms
  example O2
• Polar covalent unequal sharing of electrons
  between atoms example H2O
• Ionic complete transfer of electrons example
  NaCl
• electronegativity (EN) indicates how strongly
  an atom wants to gain an electron

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Diatomic Molecules

• Contains only two atoms. 7 naturally occurring in
  nature
• H H2
• O O2
• F F2
• Br Br2
• I I2
• N N2
• Cl Cl2

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TO PREDICT BOND TYPE

• Look at table of EN values and subtract the
  values for the 2 atoms involved in the bond
• take the absolute value
• If EN difference is
• 0 0.4 ? nonpolar covalent bond
• 0.5 1.6 ? polar covalent bond
• gt1.7 ? ionic bond

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TO DETERMINE MOLECULAR SHAPE

• Use VSEPR (valence shell electron pair repulsion)
  rules
• 1) Draw the Lewis dot structure for the molecule
• 2) Identify the central atom
• 3) Count total of electron pairs around the
  central atom
• 4) Count of bonding pairs of electrons around
  the central atom
• 5) Count of lone pairs of electrons around the
  central atom
• 6) Look at summary chart, identify shape

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Practice

• Determine the shape.1. BCl32. CaO

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Polarity

• TO DETERMINE THE POLARITY OF A MOLECULE, not a
  bond, you must know the type of bond and the
  shape.
• POLAR MOLECULES must meet 2 criteria
• Must have a polar covalent bond (EN difference
  between 0.5 and 1.6) AND

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Determining Polarity

• Must have an asymmetrical shape
• trigonal pyramidal or
• angular, or
• 2 element linear
• If both criteria are not met, it is not a polar
  molecule, it is either a nonpolar molecule or an
  ionic compound.

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Practice

• Label the following MOLECULES as polar or
  nonpolar.
• 1. NH3
• 2. CH4
• 3. HCl

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Practice

• What type of bond that will occur between each of
  the following?
• 1. BCl3
• 2. CaO

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Lewis Structures for Molecules

• Single Covalent Bonds
• Hyrdrogen Bromine
• Carbon Chlorine

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Naming Molecules

• Binary molecules-Rules
• Name the first element using the entire name
• The second element is named using the root and
  the suffix (ending) ide
• Prefixes are used to indicate the number of each
  type of atom. (Table 9-1)
• Exception-the first element will never have the
  prefix mono

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TO DETERMINE STATE OF MATTER

• 1. Determine if compound is ionic, polar, or
  nonpolar.
• 2. Calculate molar mass of compound by adding
  the mass of each of the elements in the
  compound.
• 3. Look at the state of matter chart.

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Practice

• What is the state of matter of the following
  compounds?
• 1. HBr
• 2. NH3
• 3. CaCl2

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Chapter Review Quiz

• Take the online review quiz from the textbook to
  get an idea of how you might perform on the
  multiple choice portion of the test.
• If you scored less than 14 of 20 correct 70 you
  need to spend more time studying.