Chapter 9 Molecular Geometry

Chapter 9 Molecular Geometry - Chapter 9 Chapter Molecular...

Info iconThis preview shows pages 1–18. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 9 Chapter 9 Molecular Geometry and Bonding Molecular Geometry and Bonding Theories Theories
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Lewis structures give atomic connectivity: they tell us which atoms are physically connected to which. However, do not show their overall shape) A molecule’s shape is determined by its bond angles. • Consider CCl 4 : experimentally we find all Cl-C-Cl bond angles are 109.5 ° . Therefore, the molecule cannot be planar. All Cl atoms are located at the vertices of a tetrahedron with the C at its center. Molecular Shapes Molecular Shapes
Background image of page 2
Molecular Shape of CCl Molecular Shape of CCl 4 4
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
In order to predict molecular shape, we assume the valence electrons repel each other. Therefore, the molecule adopts which ever 3D geometry minimized this repulsion. We call this process V alence S hell E lectron P air R epulsion ( VSEPR ) theory. • There are simple shapes for AB 2 and AB 3 molecules (see page 347). VSEPR Theory VSEPR Theory
Background image of page 4
Molecular Shape: Five Fundamental Geometries
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
When considering the geometry about the central atom, we consider all electrons (lone pairs and bonding pairs). When naming the molecular geometry, we focus only on the positions of the atoms. Naming Molecular Geometry
Background image of page 6
To determine the shape of a molecule, we distinguish between lone pairs (or non-bonding pairs, those not in a bond) of electrons and bonding pairs (those found between two atoms). We define the electron domain geometry by the positions in 3D space of ALL electron pairs (bonding or non- bonding). The electrons adopt an arrangement in space to minimize e - -e - repulsion. VSEPR Model VSEPR Model
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 8
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
To determine the electron pair geometry: draw the Lewis structure, count the total number of electron pairs around the central atom, arrange the electron pairs in one of the above geometries to minimize e - -e - repulsion, and count multiple bonds as one bonding pair. VSEPR Model VSEPR Model
Background image of page 10
Background image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 12
Background image of page 13

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
We determine the electron pair geometry only looking at electrons. We name the molecular geometry by the positions of atoms. We ignore lone pairs in the molecular geometry. All the atoms that obey the octet rule have tetrahedral electron pair geometries. The Effect of Nonbonding Electrons
Background image of page 14
By experiment, the H-X-H bond angle decreases on moving from C to N to O: Since electrons in a bond are attracted by two nuclei, they do not repel as much as lone pairs. Therefore, the bond angle decreases as the number of lone pairs increase. 104.5 O 107 O N H H H C H H H H 109.5 O O H H The Effect of Nonbonding Electrons on Bond Angles
Background image of page 15

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Similarly, electrons in multiple bonds repel more than electrons in single bonds. C O Cl Cl 111.4 o 124.3 o The Effect of Nonbonding Electrons and Multiple Bonds on Bond Angles
Background image of page 16
• Atoms that have expanded octets have AB 5 (trigonal bipyramidal) or AB 6 (octahedral) electron pair geometries. For trigonal bipyramidal structures there is a plane
Background image of page 17

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 18
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 79

Chapter 9 Molecular Geometry - Chapter 9 Chapter Molecular...

This preview shows document pages 1 - 18. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online