Electron Dot Structures

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.

Drawing Lewis Structures for Covalent Drawing Lewis Structures for Covalent CompoundsCompounds

Let’s 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 H’s have two electrons and all other nonmetals satisfy the “Octet Rule”5) Make sure your final structure has same number ofelectrons as you had in step 1

Electron-dot formula for Methane (CH4)

CH

H

H

HHere is a Carbon atom (4 val e-’s) and four Hydrogen atoms (1 val e- each)

Electron-dot formula for Methane (CH4)

CH

H

H

H

Now they have formed a stable molecule. Each C atom “feels” like it has a stable octet.

Each H atom “feels” like a stable “He” atom with 2e-s

Electron-dot formula for Ammonia (NH3)

NH

H

HHere is a Nitrogen atom (5 val e-’s) and three Hydrogen atoms (1 val e- each)

Electron-dot formula for Ammonia (NH3)

NH H

H

“N” now feels like it has a stable octet

Each “H” feels like it has 2 e- like Helium.

Write the electron-dot formula for CF4

CF

F

F

F

Because “F” is a halogen, it has 7 valence e-s, so you must show all 7 red dots around each “F” atom!

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.

Se F

F

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

Resonance StructuresOzone, O3

Resonance - Bonding in molecules cannot be correctly representedby a single Lewis structure

Actual structure of ozone is an average of these two structures

Benzene: Classic Case of Resonance

kekule's dream

Yes, we can see molecules!

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

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

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

Bond Energy vs Bond Length

Ionic Structure

Calcium Sulfide