Standard 3.2

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Standard 3.2

• Covalent Compounds

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Everybody on the left side of the room will be an
atom of sulfur. Everybody on the right side of
the room will be fluorine. Please hold your
elements valence electrons in your hand.
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Everybody on the left side of the room will be an
atom of sulfur. Everybody on the right side of
the room will be fluorine. Please hold your
elements valence electrons in your hand.

• Walk around the room and exchange electrons with
  your classmates in such a way that both you and
  your classmates end up being stable. Stay with
  your trading partner(s) when everyone in your
  trading group has become stable.

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Formation of covalent compounds

• Covalent compounds form when nonmetals share
  electrons.

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Formation of covalent compounds

• Covalent compounds form when nonmetals share
  electrons.
• Because all nonmetals tend to gain valence
  electrons, the valence electrons must be shared
  to complete the octets.

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Formation of covalent compounds

• Covalent compounds form when nonmetals share
  electrons.
• Because all nonmetals tend to gain valence
  electrons, the valence electrons must be shared
  to complete the octets.
• When electrons are shared between atoms, the
  bonds are relatively weak.

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Weak bonds mean

• Low melting and boiling points.

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Weak bonds mean

• Low melting and boiling points.
• Generally gases at room temperature.

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Weak bonds mean

• Low melting and boiling points.
• Generally gases at room temperature.
• Some are liquids or solids.

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Weak bonds mean

• Low melting and boiling points.
• Generally gases at room temperature.
• Some are liquids or solids.
• The solids have soft crystals.

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Weak bonds mean

• Low melting and boiling points.
• Generally gases at room temperature.
• Some are liquids or solids.
• The solids have soft crystals.
• Strong odor

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Weak bonds mean

• Low melting and boiling points.
• Generally gases at room temperature.
• Some are liquids or solids.
• The solids have soft crystals.
• Strong odor
• Flammable

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Weak bonds mean

• Low melting and boiling points.
• Generally gases at room temperature.
• Some are liquids or solids.
• The solids have soft crystals.
• Strong odor
• Flammable
• Non-electrolytes

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Polar vs nonpolar covalent molecules

• The smallest unit of a covalent compound is
  called a molecule.

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Polar vs nonpolar covalent molecules

• The smallest unit of a covalent compound is
  called a molecule.
• Molecules can be polar (a negative and positive
  region) or nonpolar.

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Polar vs nonpolar covalent molecules

• The smallest unit of a covalent compound is
  called a molecule.
• Molecules can be polar (a negative and positive
  region) or nonpolar.
• The more polar a molecule, the stronger its bonds
  are.

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Polar vs nonpolar covalent molecules

• The smallest unit of a covalent compound is
  called a molecule.
• Molecules can be polar (a negative and positive
  region) or nonpolar.
• The more polar a molecule, the stronger its bonds
  are.
• Compounds with similar polarities will dissolve
  one another (like dissolves like)

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Determining Polarity

• To determine whether a compound is polar or
  nonopolar, we need to first look at the
  difference in electronegativity between the atoms
  being bonded (table on p.265).

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Determining Polarity

• To determine whether a compound is polar or
  nonopolar, we need to first look at the
  difference in electronegativity between the atoms
  being bonded (table on p.265).
• If the difference is less than 0.40, the molecule
  is nonpolar (CH4 as an example).

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Determining Polarity

• To determine whether a compound is polar or
  nonopolar, we need to first look at the
  difference in electronegativity between the atoms
  being bonded (table on p.265).
• If the difference is less than 0.40, the molecule
  is nonpolar (CH4 as an example).
• If the difference is greater than 0.40, a Lewis
  structure is needed (CO2).

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Drawing a Lewis structure

• Begin by determining how many bonds the molecule
  contains.

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Number of bonds

• Add the total number of valence electrons needed
  by the atoms in the molecule.

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Number of bonds

• Add the total number of valence electrons needed
  by the atoms in the molecule.
• Example CO2

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Number of bonds

• Add the total number of valence electrons needed
  by the atoms in the molecule.
• Example CO2
• carbon needs 4 electrons

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Number of bonds

• Add the total number of valence electrons needed
  by the atoms in the molecule.
• Example CO2
• carbon needs 4 electrons
• each oxygen atom needs 2 electrons

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Number of bonds

• Add the total number of valence electrons needed
  by the atoms in the molecule.
• Example CO2
• carbon needs 4 electrons
• each oxygen atom needs 2 electrons
• 4 2 2 8 valence electrons needed

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Number of bonds

• Add the total number of valence electrons needed
  by the atoms in the molecule.
• Example CO2
• carbon needs 4 electrons
• each oxygen atom needs 2
• 4 2 2 8 valence electrons needed
• Divide the total by 2 (8 / 2 4 bonds)

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Drawing a Lewis structure

• Begin by determining how many bonds the molecule
  contains.
• Connect the atoms with lines representing the
  bonds. Make it symmetrical if possible.

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In this case, placing carbon in the middle with
double bonds between the carbon and each oxygen
makes it symmetrical.

• O C O

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Drawing a Lewis structure

• Begin by determining how many bonds the molecule
  contains.
• Connect the atoms with lines representing the
  bonds. Make it symmetrical if possible.
• Finally, add any unshared valence electrons as
  pairs of dots.

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Oxygen 6 valence electrons, two of which are
shared, 4 unshared electrons.
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Oxygen 6 valence electrons, two of which are
shared, 4 unshared electrons.Carbon 4 valence
electrons, all of them are shared, 0 unshared
electrons.
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Analyzing the structure

• At least one of two things in a Lewis structure
  will make it polar

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Analyzing the structure

• At least one of two things in a Lewis structure
  will make it polar
• 1) the molecule is not symmetrical

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Analyzing the structure

• At least one of two things in a Lewis structure
  will make it polar
• 1) the molecule is not symmetrical
• 2) unshared electrons on the central atom

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Analyzing the structure

• At least one of two things in a Lewis structure
  will make it polar
• 1) the molecule is not symmetrical
• 2) unshared electrons on the central atom
• If neither of the above are true, the molecule is
  nonpolar.

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CO2 is nonpolar, because the molecule is
symmetrical and there are no unshared electrons
on the central atom.
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Is H2O polar or nonpolar?
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Is H2O polar or nonpolar?

• First, we must check the difference in
  electronegativity between H and O.

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Is H2O polar or nonpolar?

• First, we must check the difference in
  electronegativity between H and O.
• 3.44 2.20 1.24 (a Lewis structure will be
  needed)

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Is H2O polar or nonpolar?

• First, we must check the difference in
  electronegativity between H and O.
• 3.44 2.20 1.24 (a Lewis structure will be
  needed)
• Calculate the number of bonds.

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Is H2O polar or nonpolar?

• First, we must check the difference in
  electronegativity between H and O.
• 3.44 2.20 1.24 (a Lewis structure will be
  needed)
• Calculate the number of bonds.
• each H needs 1 electron, O needs 2 electrons
• 4 / 2 2 bonds

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Is H2O polar or nonpolar?

• Try to draw a symmetrical molecule containing 2
  bonds.
• H O H

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Is H2O polar or nonpolar?

• Try to draw a symmetrical molecule containing 2
  bonds.
• Add dots for any unshared valence electrons.
• hydrogen, 1 valence electron, 1 shared electron
• oxygen, 6 valence electrons, 2 shared electrons

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Is H2O polar or nonpolar?

• Even though the molecule is symmetrical, there
  are unshared electrons on the central atom (O)
  making water a polar molecule.

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Is PF3 polar or nonpolar?
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Is PF3 polar or nonpolar?

• Electronegativity difference of 1.79, a Lewis
  structure is needed.

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Is PF3 polar or nonpolar?

• Electronegativity difference of 1.79, a Lewis
  structure is needed.
• 3 bonds

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Is PF3 polar or nonpolar?

• Electronegativity difference of 1.79, a Lewis
  structure is needed.
• 3 bonds
• 2 unshared electrons on P, 6 unshared electrons
  on each F.
• Molecule is polar.

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Is AsH3 polar or nonpolar?
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Is AsH3 polar or nonpolar?

• Electronegativity difference of 0.02, molecule is
  nonpolar.

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Is SO2 polar or nonpolar?
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Is SO2 polar or nonpolar?

• Electronegativity difference is 0.86, a Lewis
  structure is needed.

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Is SO2 polar or nonpolar?

• Electronegativity difference is 0.86, a Lewis
  structure is needed.
• 3 bonds
• O S O

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Is SO2 polar or nonpolar?

• Electronegativity difference is 0.86, a Lewis
  structure is needed.
• 3 bonds
• O S O

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Is SO2 polar or nonpolar?

• Electronegativity difference is 0.86, a Lewis
  structure is needed.
• 3 bonds
• add the unshared electrons
• O S O
• When two electrons are left unpaired, one of them
  must be moved.

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Is SO2 polar or nonpolar?

• Electronegativity difference is 0.86, a Lewis
  structure is needed.
• 3 bonds
• add the unshared electrons
• O S O
• Always move the electron to the more
  electronegative element.

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Is PCl5 polar or nonpolar?
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Is PCl5 polar or nonpolar?

• Electronegativity difference tells us a Lewis
  structure will be needed.

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Is PCl5 polar or nonpolar?

• Electronegativity difference tells us a Lewis
  structure will be needed.
• With a total of 8 electrons needed, we calculate
  4 bonds are present, but 4 bonds are not enough.

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Is PCl5 polar or nonpolar?

• Electronegativity difference tells us a Lewis
  structure will be needed.
• With a total of 8 electrons needed, we calculate
  4 bonds are present, but 4 bonds are not enough.
• When this happens, you will only have single
  bonds and you use the minimum number of bonds
  possible (5 in this case).

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Structures such as this require an expanded
octet, meaning the central atom ends up with more
than 8 valence electrons.
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Unshared electrons are distributed just like in a
regular Lewis structure.
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Unshared electrons are distributed just like in a
regular Lewis structure. This molecule is
nonpolar.
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Is BF3 polar or nonpolar?
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Is BF3 polar or nonpolar?

• Electronegativity difference indicates that a
  Lewis structure is needed.

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Is BF3 polar or nonpolar?

• Electronegativity difference indicates that a
  Lewis structure is needed.
• With 8 electrons needed, 4 bonds should be needed.

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Is BF3 polar or nonpolar?

• Electronegativity difference indicates that a
  Lewis structure is needed.
• With 8 electrons needed, 4 bonds should be needed.

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Is BF3 polar or nonpolar?

• Boron should be involved in all 4 bonds, but it
  only has 3 valence electrons to donate. Only 3
  bonds can exist in this molecule.

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Is BF3 polar or nonpolar?

• Molecules in which boron is the central atom will
  have an incomplete octet for the boron.

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Is BF3 polar or nonpolar?

• Molecules in which boron is the central atom will
  have an incomplete octet for the boron.
• This molecule is nonpolar.

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