LEWIS STRUCTURES

Lewis Dot Diagrams

Show the valence electrons for an element.

Steps.1. Draw element Symbol2. Place the number of electrons around

the symbol. One dot per electron. Ex. Carbon

Examples

Silicon

Oxygen

Fluorine

Lewis Structures

Combining of the dot diagrams to show bonding and to predict shape.

Steps for Lewis Structures

1. Add up total number of valence electrons.2. Draw a skeleton (Carbon, the solo element,

or the most electronegative element goes in the middle)★Hydrogen and the Halogens CANNOT be in the center.

3. Distribute the electrons as PAIRS. Start from the outside and move inward.

4. Count and adjust electrons till each element has 8. (except Hydrogen)

Examples

CF4

PH3

H2O

O2(Careful)

Polyatomics

Same as compounds but you must add/subtract the charge from the electrons in step 1.

And place the structure in brackets with the charge outside.

Ex. Hydroxide. How many electrons in a neutral OH?7 How many in OH-?8

Examples

SO42-

NH4+

CO32-

Review Draw the Lewis structures for:

CO2

F2

CH2Cl2

SO32-

VSEPR THEORY (A FANCY WAY TO PREDICT SHAPES)

VSEPR

Stands for “Valence shell Electron pair Repulsion”

V-Valence S-Shell E-Electron P-Pair R-Repulsion Basically Electrons don’t like each other

very much!

5 Shapes

Tetrahedral- four single bonds Trigonal Pyramidal- 3 single bonds and 1

lone pair Trigonal planar – 2 single, 1 double Bent- 2 bonds (any type) and lone pairs Linear- 2 bonds no lone pairs or just 2

atoms

PracticeDraw the Lewis structure and predict the shape

CF4

Tetrahedral

PH3

Trigonal Pyramidal

SO3

Trigonal Planar

H2O Bent

Predict the shape of the following PF3

Trigonal Pyrimidal

NO3-

Trigonal Planar

SO42-

Tetrahedral

SF2

Bent

SiO2

Linear

LAB TIME!