Section 12.4

Structure of Molecules

B. Ionic bonding and Structures of Ionic Compounds

• Polyatomic ions work in the same way as simple ions– The covalent bonds hold the polyatomic ion together so it

behaves as a unit

Ionic Compounds Containing Polyatomic Ions

Section 12.4

Structure of Molecules

• Writing Lewis Structures for Polyatomic Ions

Section 12.4

Structure of Molecules

[SO4]2-

2-

Section 12.4

Structure of Molecules

[NO2]-

-

Section 12.4

Structure of Molecules

[NH4]+

+

Section 12.4

Structure of Molecules

1. SWBAT understand molecular structure, be able to predict molecular geometry from the number of electron pairs and to apply the VSEPR model to molecules with double bonds in a virtual laboratory.

Objectives

Section 12.4

Structure of Molecules

A. Molecular Structure

• The atoms in a molecule have a three dimensional arrangement,– Water - bent

LQHS

Section 12.4

Structure of Molecules

A. Molecular Structure

• Linear structure – atoms in a line

– Carbon dioxide

Section 12.4

Structure of Molecules

A. Molecular Structure

• Trigonal planar – atoms in a triangle

– BF3

Section 12.4

Structure of Molecules

A. Molecular Structure

• Tetrahedral structure

– Methane CH4

Section 12.4

Structure of Molecules

B. The VSEPR Model

• Valence shell electron pair repulsion (VSEPR) model – Molecular structure is determined by minimizing

repulsions between electron pairs

Section 12.4

Structure of Molecules

B. The VSEPR Model

– 180o - linear – (Note, this is an ionic compound exception AND an octet

rule exception!)

Two Pairs of Electrons

• BeCl2

Section 12.4

Structure of Molecules

B. The VSEPR Model

– 120o – trigonal planar

Three Pairs of Electrons

• BF3

Section 12.4

Structure of Molecules

B. The VSEPR Model

– 109.5o – tetrahedral

Four Pairs of Electrons

• CH4

Section 12.4

Structure of Molecules

B. The VSEPR Model

Section 12.4

Structure of Molecules

B. The VSEPR Model

Section 12.4

Structure of Molecules

C. Molecules with Double Bonds

When using VSEPR model to predict molecular geometry of a molecule

• a double bond is counted the same as a single electron pair

LQHSVirtual Lab