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 SO4

2-

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!