Electron Dot Structures

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Electron Dot Structures
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Lewis Structures
- Diagrams that show the bonding between atoms of
a molecule, and the lone pairs of electrons that
may exist in the molecule.
- Introduced by Gilbert Lewis in 1916.
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Drawing Lewis Structures for Covalent Compounds
Lets try SiH4 (silane)
1) First count all the valence electrons
2) Decide which atom will be your central atom
-Carbon is always in the center -Hydrogen is
never in the center -If no carbon, least
electronegative element is placed in center
3) Decide which atom will be your central atom
and then connect the atoms by electron-pair bonds
4) Make sure all Hs have two electrons and all
other nonmetals satisfy the Octet Rule
5) Make sure your final structure has same number
of electrons as you had in step 1
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Electron-dot formula for Methane (CH4)
H
H
C
H
H
Here is a Carbon atom (4 val e-s) and four
Hydrogen atoms (1 val e- each)
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Electron-dot formula for Methane (CH4)
H
Now they have formed a stable molecule. Each C
atom feels like it has a stable octet.
H
C
H
Each H atom feels like a stable He atom with
2e-s
H
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Electron-dot formula for Ammonia (NH3)
H
N
H
Here is a Nitrogen atom (5 val e-s) and three
Hydrogen atoms (1 val e- each)
H
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Electron-dot formula for Ammonia (NH3)
N now feels like it has a stable octet
Each H feels like it has 2 e- like Helium.
N
H
H
H
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Write the electron-dot formula for CF4
Because F is a halogen, it has 7 valence e-s,
so you must show all 7 red dots around each F
atom!
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Write the Electron-Dot Formula for SeF2
Because F is in Group 17, they have 7 valence
e-s, so they must have 7 red dots around them.
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Formaldehyde CH2O
Some elements, especially C, N, and O can share
more than one pair of electrons!!
Two pairs of electrons shared double bond
Three pairs of electrons shared triple bond
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Resonance StructuresOzone, O3
Resonance - Bonding in molecules cannot be
correctly represented by a single Lewis structure
Actual structure of ozone is an average of these
two structures
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Benzene Classic Case of Resonance
kekule's dream
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Yes, we can see molecules!
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Bond Energy vs Bond Length
Bond Bond length (ppm) Bond Energy (kJ/mol) Bond Bond length (ppm) Bond Energy (kJ/mol)
H-H 74 436 C-C 154 346
F-F 141 159 C-N 147 305
Cl-Cl 199 243 C-O 143 358
Br-Br 228 193 C-H 109 418
I-I 267 151 C-Cl 177 327
H-F 92 569 C-Br 194 285
H-Cl 127 432 N-N 145 163
H-Br 141 366 N-H 101 386
H-I 161 299 O-H 96 459
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Bond Energy vs Bond Length
Bond Bond length (ppm) Bond Energy (kJ/mol) Bond Bond length (ppm) Bond Energy (kJ/mol)
H-H 74 436 C-C 154 346
F-F 141 159 C-N 147 305
Cl-Cl 199 243 C-O 143 358
Br-Br 228 193 C-H 109 418
I-I 267 151 C-Cl 177 327
H-F 92 569 C-Br 194 285
H-Cl 127 432 N-N 145 163
H-Br 141 366 N-H 101 386
H-I 161 299 O-H 96 459
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Bond Energy vs Bond Length
Bond Bond length (ppm) Bond Energy (kJ/mol) Bond Bond length (ppm) Bond Energy (kJ/mol)
H-H 74 436 C-C 154 346
F-F 141 159 C-N 147 305
Cl-Cl 199 243 C-O 143 358
Br-Br 228 193 C-H 109 418
I-I 267 151 C-Cl 177 327
H-F 92 569 C-Br 194 285
H-Cl 127 432 N-N 145 163
H-Br 141 366 N-H 101 386
H-I 161 299 O-H 96 459
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Ionic Structure
Calcium Sulfide