Transcript CHEM121 Lecture Ch4 student

CHEM 121
Chapter 4
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Ionic v. Covalent Substances
• Ionic substances:
•
•
• Ionic bonds:
•
- + - + - +
+ - + - + - + - + - +
+ - + - + -
• Covalent substances:
•
• Covalent bonds:
•
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Covalent Bonds
• Form when atoms share electrons to form molecules
• Usually between nonmetal and nonmetal
• Atoms with….
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•
•
•
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Covalent Bonding
H
F
+
+
H
F
H H
F F
H
F
H
F
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More Covalent Compounds
C + H
C
+4 H
Carbon atom:
•
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Another Covalent Compound
N + H
N
+3 H
Nitrogen atom:
•
•
•
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One more Covalent Compound
O + H
O
+2 H
Oxygen atom:
•
•
•
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Lewis Dot Structure Hints
• Draw only the ____________ electrons
• Carbon group elements want ____________
• Nitrogen group elements want ___________
and…
• Oxygen group elements want ____________
and…
•
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Drawing Lewis Dot Structures
1. Count the total number of valence electrons
2. Arrange atoms so that at least one bond
connects them
3. How many electrons are left?
These are lone pairs!
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3-minute review
Draw the Lewis Structures for each of the
following covalent compounds:
CH3Cl
PH3
H2O2
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Lewis Dot Structures for Ions
• Polyatomic ions are ________________ bonded
• When counting valence e-, include _____________
How many valence e- total in each of the following?
NO3-
SO42-
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3-minute review
How many valence electrons should be used to
draw the Lewis Structure of acetate (C2H3O2-)?
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Multiple Bonds
O + C + O
N +
N
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3-minute review
Draw the Lewis Structures for each of the
following covalent molecules:
C2F6
C2F4
C2F2
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Resonance Structures
Molecules with more than one Lewis Structure
• Usually involves swapping double bond e- with lone
pair e- or other double bond e• True structure is a _______________
O3
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3-minute review
Draw 2 resonance structures for the nitrate ion:
NO3-
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Exceptions to the Octet Rule
• Hydrogen
•
• Group 3A Elements
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•
•
• Third Row (and later) Elements
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•
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Examples: PCl3 and PCl5
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Shapes of Molecules
VSEPR:
Minimize e- repulsion
e- groups pushed as far apart as possible
Electron groups:
•
Note: double, triple bonds count as ONE group
•
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Basic Molecular Shapes
2 electron groups
3 electron groups
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Basic Molecular Shapes: 4 electron groups
bent
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Electronegativity
Electronegativity:
(EN)
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Electronegativity & Bond Type
________________________ tells us whether a bond is
more ionic or more covalent
• Ionic bond:
• Covalent bond:
• Some difference in electronegativity:
• No difference in electronegativity:
• Polar bonds create a
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Polarity of Molecules
Polar bond: difference in electronegativities of bonded atoms
H-H
F-F
H-F
O
H
H
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Polarity of Molecules
H
H
C
Add polar bonds (head to tail)
H
H
Molecules with polar bonds may not be polar overall!
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Covalent Compounds
• Combination of two different elements
Rules for Naming
1. ______________________ element first;
______________________ element is second.
2. Second element: “root”-ide
3. Add Greek numerical prefixes
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Naming Covalent Compounds
Example: CS2
1. Which element is less EN?
2. Second element is root-ide
3. Add prefix
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Naming Covalent Compounds
Example: N2O
1. Which element is less EN?
2. Second element is root-ide
3. Add prefix
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3-minute practice
Write the name for the following compounds:
• CF4
• P2O5
• SCl6
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Acetaminophen
Draw in lone pairs.
How many single bonds are in this molecule?
How many double bonds?
Are some bonds nonpolar?
Are some bonds more polar?
(Assume C and H have similar electronegativities.)
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