C

HAPTER

9: M

OLECULAR GEOMETRY AND BONDS

J

ANUARY

28

TH

, 2013

 Do Now: Calculate the ∆H: C 2 H 4 + HCN  CH 3 CH 2 CN

M

OLECULE SHAPE

 How do we determine the shape of a molecule?

 How are bonds related to the location of electrons?

 Draw CO 2 , how many electron domains are located on the central carbon?

VSEPR T

HEORY

 States: “Best arrangement of a given number of electron domains is the one that minimizes the repulsions among them”  Predict the difference between electron-domain geometry and molecular geometry.

 How do we use VSEPR Theory:    Draw lewis structure of molecule or ion and count number of electron domains around central atom.

Determine electron-domain geometry Using table determine (eventually *memorize*) molecular geometry

P

RACTICE

 Predict the molecular geometry of:   O 3 SnCl 3  Compare and contrast:    H 2 O CH 4 NH 3  Explain the ideal bond angles.

W

ORK IT OUT

 How are all the bond angles related to one another?

 With a partner or small group, discuss why it is possible that all these angles are so large, similar.

 In fancy terms: Non-bonding electrons give off greater repulsive forces therefore compressed bond angles.

 ** NOTE: double bonded atoms tend to exert a greater repulsive force as well.

P

RACTICE

:

 Determine the following molecular geometries:     SF 4 IF 5 BrF 3 ICl 4 -

L

ARGER THAN LIFE

…

 Large molecules need to be broken down into their smaller components:  Draw CH3COOH (use VSEPR for each central atom)

P

OLARITY

 Why is polarity important?

 How do we determine polarity?

  Bonds: Molecules:  Predict the polarity of the following:    BrCl SO 2 SF 6

E

XPLANATIONS

 How do we explain bonding?

 How is energy related to distance of covalent bonds?

 Why is there a sharp increase with shorter distance?

 All in all: bond length is distance at which the attractive forces between unlike charges are balanced by repulsive forces within the molecule