# LEWIS STRUCTURES. Lewis Dot Diagrams  Show the valence electrons for an element. Steps. 1. Draw element Symbol 2. Place the number of electrons around.

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LEWIS STRUCTURES

Lewis Dot Diagrams  Show the valence electrons for an element. Steps. 1. Draw element Symbol 2. 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  CF 4  PH 3  H 2 O  O 2 (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  SO 4 2-  NH 4 +  CO 3 2-

Review Draw the Lewis structures for:  CO 2  F 2  CH 2 Cl 2  SO 3 2-

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

Practice Draw the Lewis structure and predict the shape  CF 4  Tetrahedral  PH 3  Trigonal Pyramidal  SO 3  Trigonal Planar H2OH2O  Bent

Predict the shape of the following  PF 3  Trigonal Pyrimidal  NO 3 - Trigonal Planar  SO 4 2-  Tetrahedral  SF 2  Bent  SiO 2  Linear

LAB TIME!

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