“The Shapes of Small Molecules”

Honors ChemistryChapter 8.1 notes

Legos:Does this bring back any good memories???

A. Structural Formula

1. Ex: Ammonia NH3

2. Boring, 2 Dimensional…

B. Ball and Stick Model1. Def – Ball represents atom’s nucleus

and inner electrons. Sticks represent bonds between atoms.

2. 3-Dimensional!3. Shapes are symmetrical.

a. Equal distance separating atoms

I. Molecular Geometry

b. Why?

*electrons repel other electrons to form symmetry

4. VSEPR Theory

a. Valence-shell electron pair repulsion theory

b. Def – in a small molecule, the pairs of electrons are arranged as far apart from each other as possible.

*Note: this does not apply in all situations!

Ex: transition metals

II. Molecular GeometryContinued…

A. Linear

1. Def – straight line angles (180°)

2. Ex: O2, HCl, CO2

B. Trigonal Planer

1. Def – Triangular and flat (120°)

2. Ex: BCl3,

3. Usually 1 central atom

C. Tetrahedral

1. Def – means shape with 4 surfaces (109.5°)

2. Ex: CH4

3. Angle is not 90°! (Fig 8-7)

D. Pyramidal or Trigonal Pyramidal

1. Def – 3 corners with 1 pair of unshared electrons

2. Bond Angle = 107°

3. why? Unpaired electrons take up more room.

4. Ex: NH3

E. Bent

1. Def – Not linear !

2. Bond Angle = 105°

3. Ex: H2O

F. Others…

1. T-shaped ClF3

2. Square Planar XeF4

3. Trigonal Bipyramidal PF5

4. Octahedral SF6

1. Identify the following molecular shapes and bond angles:

a. H2O

b. CF4

c. NCl3d. CO2

e. NF3

f. BF3

g. HCNh. NO3

8.1 assignment

Bent – 105

Tetrahedral – 109.5 Trigonal pyramidal – 107

Linear – 180 Trigonal pyramidal – 107

Trigonal Planer – 120

Linear – 180 Trigonal Planer – 120