To understand molecular structure and bond angles
15
Section 12.4 Structure of Molecules 1. To understand molecular structure and bond angles 2. To learn to predict molecular geometry from the number of electron pairs 3. To learn to apply the VSEPR model to molecules with double bonds Objectives
description
Objectives. To understand molecular structure and bond angles To learn to predict molecular geometry from the number of electron pairs To learn to apply the VSEPR model to molecules with double bonds. - PowerPoint PPT Presentation
Transcript of To understand molecular structure and bond angles
Section 12.4
Structure of Molecules
1. To understand molecular structure and bond angles
2. To learn to predict molecular geometry from the number of electron pairs
3. To learn to apply the VSEPR model to molecules with double bonds
Objectives
Section 12.4
Structure of Molecules
Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red cells of the blood in mammals and other animals. Hemoglobin transports oxygen from the lungs to the rest of the body, such as to the muscles, where it releases the oxygen load.
Section 12.4
Structure of Molecules
Draw possible structures that you can think of for the molecules below. Think in three dimensions.
A2, AB, AB2, AB3, AB4, AB5, AB6
Section 12.4
Structure of Molecules
Structures for some simple molecules
Section 12.4
Structure of Molecules
A. Molecular Structure
• Three dimensional arrangement of the atoms in a molecule
– Water, H2O - bent
Section 12.4
Structure of Molecules
A. Molecular Structure
• Linear structure – atoms in a line
– Carbon dioxide, CO2
Section 12.4
Structure of Molecules
A. Molecular Structure
• Trigonal planar – atoms in a triangle
– Boron Trifluoride, 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 – Pairs of electrons in bonds and “lone pairs” influence
the molecular structure
2 balloons 3 balloons 4 balloons 5 balloons 6 balloons
Section 12.4
Structure of Molecules
B. The VSEPR Model
– 180o - linear
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
Predicting Molecular Structure using the VSEPR model1.Draw the Lewis structure2.Count the pairs of electrons and arrange to minimize repulsions3.Determine the positions of the atoms4.Name the molecular structure according to the position of the atoms not the lone electron pairs
e.g. NH3 has four pairs of electrons surrounding the N atom which form a tetrahedron. The molecule is named however as a trigonal pyramid
Section 12.4
Structure of Molecules
B. The VSEPR Model
molecular shapes 2
H2O
Predicting molecular shapes
molecular shapes
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 as the same as a single electron pair
ethylene
H-C-H angle is 120o
