Friday, Feb. 21st:

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Friday, Feb. 21st A DayMonday, Feb. 24th
B DayAgenda

• Go over 6.1 quiz
• Review Lewis structures
• Finish Section 6.2
• Lewis structures with double and triple bonds,
  naming covalent compounds
• Homework
• Practice pg. 205 1, 2
• Section 6.2 review, pg. 207 1-10
• Concept Review Drawing and Naming Molecules
• Next time Lewis structures on iPads

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Homework Questions?

• Practice pg. 202 1,2
• Practice pg. 203 1,2

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Sec. 6.1 quiz Covalent Bonds

• Which statement is true about a molecule of H2?
• Each atom has an electron configuration like that
  of helium.
• It is less stable than either of the hydrogen
  atoms by itself.
• The electrons from both atoms travel within the
  molecular orbital.
• Both (a) and (c)

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Sec. 6.1 quiz Covalent Bonds

• Which statement is true about a molecule of H2?
• Each atom has an electron configuration like the
  of helium.
• It is less stable than ether of the hydrogen
  atoms by itself.
• The electrons from both atoms travel within the
  molecular orbital.
• Both (a) and (c)

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Sec. 6.1 quiz Covalent Bonds

• A single covalent bond involves the sharing of
  how many electrons?
• 2 HH
• If two covalently bonded atoms move closer than a
  distance of the bond length, the potential energy
  of the atoms
• Increases
• (the bond length is measured when the atoms are
  at their lowest potential energy any other
  distance would be an increase in energy)

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Sec. 6.1 quiz Covalent Bonds

• The electrons involved in the formation of a
  covalent bond are
• Valence electrons
• Bond energy is the energy
• Required to break one mole of similar bonds in a
  compound

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Sec. 6.1 quiz Covalent Bonds

• Bond length between two bonded atoms is
• the separation at which their potential energy is
  minimum
• Which compound most likely has the greatest bond
  energy?
• HF
• (shorter bond length stronger bond)

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Sec. 6.1 quiz Covalent Bonds

• Nonpolar covalent bonds are not common because
• one atom usually attracts electrons more strongly
  than the other

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Sec. 6.1 quiz Covalent Bonds

• The bond between which pair of elements listed in
  the table will most likely have the least ionic
  character?
• O and H
• Find difference in electronegativity,
• smallest difference least ionic
• Na and Cl 2.3
• H and Cl 1.0
• O and H 0.8
• Na and O 2.1

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Sec. 6.1 quiz Covalent Bonds

• Which of the following substances has the lowest
  boiling point?
• CuF
• H2O
• CO
• NaCl

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Sec. 6.1 quiz Covalent Bonds

• Which of the following substances has the lowest
  boiling point?
• CuF (ionic compound)
• H2O (liquid at room temperature)
• CO (gas at room temperature)
• NaCl (ionic compound)

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Lewis Structure Review

• Determine the number of valence electrons in each
  atom and in the compound.
• Arrange the atoms.
• Remember, carbon likes to be in the middle and
  likes to bond with itself. Hydrogen can only
  have 1 bond! Compounds like to be symmetrical.
• Distribute the dots.
• Draw the bonds. Change each shared pair of dots
  between symbols to a line.
• Verify the structure!

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Lewis Structure Review

• Draw the Lewis dot structure for the following
• H2S
• C2H6
• CH3OH
• 4. BF3 (Hint boron DOES NOT
• obey the octet rule)

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Multiple Bonds

• Atoms can share more than 1 pair of electrons in
  a covalent bond.
• Consider the Lewis structure for oxygen, O2.
• Each oxygen atom has 6 valence electrons for a
  total of 12 electrons.
• If you distribute the dots around the oxygen
  atoms, the octet rule will not be satisfied and
  oxygen will not be happy.

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Double Bonds

• To make an octet, each oxygen atom needs two more
  electrons.
• The two atoms share four electrons.
• Double bond a covalent bond in which two atoms
  share two pairs of electrons.
• Carbon, oxygen, and nitrogen atoms like to form
  double bonds.

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Sample Problem C, pg. 205

• Draw a Lewis structure for formaldehyde, CH2O.
• 1. Determine the number of valence electrons.
• 4 1 1 6 12 total
• 2. Arrange the atoms so that carbon is the
  central atom.
• O H C H

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Sample Problem C, pg. 205 (Cont.)

• 3. Distribute one pair of dots between each of
  the atoms and the rest, in pairs, around the
  atoms. Carbon does not have an octet. To get an
  octet, move an unshared pair from the oxygen to
  between the oxygen and the carbon.
• Change each bonding pair to a long dash. Two
  pairs of dots represent a double bond.
• Verify the structure!

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Additional Double Bond Examples

• Draw the Lewis structures for the following
  molecules
• C2H4
• N2F2
• O2

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Triple Bonds

• Consider the Lewis structure for nitrogen, N2.
• Each nitrogen atom has 5 valence electrons for a
  total of 10 electrons.
• If you distribute the dots around the nitrogen
  atoms, the octet rule will not be satisfied and
  nitrogen will not be happy.

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Triple Bonds

• For N2 to make an octet, each atom needs three
  more electrons.
• The two atoms share six electrons.
• Triple bond a covalent bond in which two atoms
  share three pairs of electrons.
• Carbon and nitrogen atoms like to form triple
  bonds.

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Additional Practice

• Draw the Lewis structure for HC2Cl.
• Determine number of valence electrons 16
• Arrange the atoms so that carbon is in the
  middle.
• H C C Cl
• Distribute the dots
• H C C Cl
• Carbon is NOT happy, each C atom needs
• 2 more electrons.

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Additional Practice (cont.)

• To get an octet around carbon, move 2 pairs of
  electrons in-between the 2 carbon atoms
• H C C Cl
• Draw the bonds
• H C C Cl
• 5. Verify the structure!

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Resonance Structures

• Some molecules, such as ozone, O3, cannot be
  represented by a single Lewis structure.
• When a molecule has two or more possible Lewis
  structures, the two structures are called
  resonance structures.

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Resonance Structures

• Resonance Structure any one of 2 or more
  possible configurations of the same compounds
  that have identical geometry but different
  arrangements of electrons.
• When drawing resonance structures, a
  double-headed arrow is placed between the
  structures to show that the actual model is an
  average of the possible structures.

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Resonance Structure Example

• Draw the Lewis structure for the nitrite ion,
  NO2-
• Count the valence electrons
• 5 6 6 1 18 electrons total
• Arrange the atoms
• O N O
• 3. Distribute dots and draw bonds
• O N O
• N does not have a complete octet ?

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Resonance Structure Example

• In order for N to have a complete octet, we need
  a double bond, but where do we put it?
• O N O
• or
• O N O
• The actual structure is a combination of these
  two structures

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Resonance Structure Example

• This is how the Lewis structure for NO2 - would
  be shown
• -
• O N O O N O
• Draw each structure and put between
  them.
• (The brackets are needed because NO2 is an ion)

-
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Naming Covalent Compounds

• The first element named is usually the first one
  written in the formula. It is usually the
  less-electronegative element.
• The second element named has the ending
• -ide.
• Unlike the names for ionic compounds, the names
  for covalent compounds must often distinguish
  between two different molecules made of the same
  elements.
• CO carbon monoxide
• CO2 carbon dioxide

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Naming Covalent Compounds

• This system of prefixes is used to show the
  number of atoms of each element in the molecule.

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Naming Covalent Compounds

• Prefixes can be used to show the numbers of each
  type of atom in diphosphorus pentasulfide.

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Naming Covalent Compounds

• Prefixes are added to the first element only if
  the molecule has more than 1 atom of that
  element.
• N2O dinitrogen oxide
• SO3 sulfur trioxide
• Vowels a and o are dropped from a prefix if the
  word begins with a vowel.
• CO carbon monoxide NOT carbon monooxide
• N2O4 dinitrogen tetroxide NOT dinitrogen
  tetraoxide

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Homework

• Practice pg. 205 1, 2
• Section 6.2 review, pg. 207 1-10
• Concept Review Drawing and Naming Molecules
• Next Time
• Lewis Dot practice on iPads
• Lewis Dot Quiz