Covalent Bonding – Lewis Dot Diagrams Packet pages 3-7.
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Transcript of Covalent Bonding – Lewis Dot Diagrams Packet pages 3-7.
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Covalent Bonding – Lewis Dot Diagrams
Packet pages 3-7
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Representations of Molecules
Lewis Structures of compoundLewis Structures of compound
HH22 = Molecular Formula = Molecular Formula
H-H = Structural Formula H-H = Structural Formula
[- [- represents 1 pair of shared electronsrepresents 1 pair of shared electrons]]
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Halogens
Share 1 pair (2 electrons): form single covalent bondShare 1 pair (2 electrons): form single covalent bond
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Single Bonds• Hydrogen and Halogens for Single Bonds
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Single bond = 2 electrons are shared
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Double Bonds
Oxygen and Sulfur
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Double bond = ___ electrons shared
4
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Triple Bonds
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Triple bond = ___ electrons shared
6
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Structure of Covalent Compounds
NOT necessarily empirical - a lot are molecular….we can keep adding atoms!
glucose lipids
C6H12O6 (fats)
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STEPS for drawing Lewis Diagrams
1. Arrange symbols on paper the way think atoms are arranged
- Diatomics easy – next to each other- Hydrogens always terminal (on outside)- Atom with least attraction (lowest electronegativity) for shared electrons placed in center
H2
H2OH HH O H
CO2
O C O
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Steps for drawing Lewis Diagrams
2. Add up # valence electrons all atoms
H2 H2O
H H H O H
CO2
O C O
2 8 16
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Rules for drawing Lewis Diagrams3. Distribute electrons, start with single bonds start with single bonds
(electron pairs) between all atoms(electron pairs) between all atoms H2 H2O
H H H O H
CO2
O C O
2 8 16
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Rules for drawing Lewis Diagrams4. Test validity (2 tests)
1. A) # dots = # valence electrons found in rule 2
2. B) Every atom has octet (except H – only wants 2)
H2 H2O
H H H O H
CO2
O C O
2 8 16Bonding electrons get counted 2 times –once for each atom sharing themBonding electrons get counted 2 times –once for each atom sharing them
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Assessing Lewis Diagrams
• If dot structure passes both tests, you’re finished
• If fails one or both tests, try again
• If single bonds don’t work - try multiple bonds– Single bond = 2 electrons shared– Double bond = 4 electrons shared– Triple bond = 6 electrons shared
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CO2
O C O
16
CO2
O C O
16CHECK AGAIN1. A) # dots = # valence
electrons found in rule 2
2. B) Every atom has octet (except H – only wants 2)
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O=C=O
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Try some examples
• H2, F2, HF, O2, N2
• Step 1: Draw symbols the way think atoms are arranged
–Diatomics easy – atoms next to each other!
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Drawing Lewis Diagrams
H HH H
Step 2: Count up the Step 2: Count up the valence electronsvalence electrons
Each H has 1 valence Each H has 1 valence electron so the total = 2electron so the total = 2
Step 3: Distribute the valence electrons, Step 3: Distribute the valence electrons, starting with single bonds between all atomsstarting with single bonds between all atoms
::
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Testing Lewis Diagrams
H HH H::Test 1: Test 1: 2 dots in 2 dots in diagram = diagram = 2 valence 2 valence electronselectrons
Test 2:Test 2:Each H has 2 Each H has 2 valence electrons valence electrons (Remember H (Remember H only wants 2)only wants 2)
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Testing Lewis Diagrams
F FF FStep 1Step 1
Step 2Step 2 2 X 7 = 14 valence electrons2 X 7 = 14 valence electrons
Step 3Step 3 F FF F:: :: ::....
....
....
....
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Try HF
H FH FStep 1Step 1
Step 2Step 2 7 + 1 = 8 valence electrons7 + 1 = 8 valence electrons
Step 3Step 3 H FH F:: ::....
....
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O OO OStep 1:Step 1:
Step 2:Step 2: 2 X 6 = 12 valence electrons2 X 6 = 12 valence electrons
Step 3:Step 3: O OO O:::: ::....
....
....
Step 4: Test failedStep 4: Test failed
No Good!No Good!
Try O2
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Try O2 Again!
O OO OStep 1:Step 1:
Step 2:Step 2: 2 X 6 =122 X 6 =12
Step 3: Distribute electrons (single bond between Step 3: Distribute electrons (single bond between atoms didn't work so try a double bond)atoms didn't work so try a double bond)
::::....
....
....
....
Step 4: Test!Step 4: Test!
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Try N2
N NN NStep 1:Step 1:
Step 2:Step 2: 2 X 5 = 10 electrons2 X 5 = 10 electrons
Step 3: Distribute electrons starting with a single Step 3: Distribute electrons starting with a single bond between the nitrogen atomsbond between the nitrogen atoms
: : ....
:: .... ::
Step 4: TestStep 4: Test
No Good!No Good!
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Try N2 with a double bond
N NN N:::::: ::....
No Good!No Good!
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Try N2 with a triple bond
N NN N:::::::: ::
Step 4: TestStep 4: Test