Chapter 8

Shape of molecules

VSEPR-

• Stands for: Valence-shell electron pair repulsion theory.

• States that pairs of valence e- arrange as far apart as possible.

Ball-and-stick models-

• 3D physical model – ball = atom– Sticks/spring = single bonds– curved springs/more then one spring =

multiple bonds.

Bond angle-

• The geometric angle between 2 adjacent bonds in a molecule.

Drawing 3D

• Single

• Double

• Triple

• Lone Pairs

CH4

Common Shapes: – Linear -atoms connect in a straight line.

– Lewis Dot Diagram:

Common Shapes:

– Bent molecules have a lone pair • Involves O or S

• Lewis Dot Diagram: 104.5°

Common Shapes:

– Trigonal planar- triangular and flat shape.• Involves B or Al

– Lewis Dot Diagram:

Common Shapes:

– Tetrahedral –3 sided pyramid w/ four surfaces.

• Involves C or Si

– Lewis Dot Diagram:

Common Shapes:

– Pyramidal -central atom bonded to 3 other atoms and has an unshared pair of valence e-

• Involves N or P

– Lewis Dot Diagram:107.5°

All geometries in book w/ names and angles – section 8-1

LinearTetrahedral

Trigonal planar

Pyramidal

Bent

104.5°

107.5°

Bond length-

• Down a group bonds lengthen

• Multiple bonds (double/triple) are shorter than single.

Skagen’s Homepage Chemistry Resources 1st slide

Chapter 8

Shape of molecules

8-2 PolarityDipole-

• One side of a molecule has a negative charge and the other side has a positive charge

Polarity-

• Is determined by the shape of a molecule and polarity of its bonds

Polar

Non-polar

Determining Polarity

Polar

• Non symmetrical

• Pyramidal and Bent are always polar - other shapes can be as well

• Symmetrical

• Linear, trigonal planer, and tetrahedral are possible non polar molecules

Non-Polar

Non-symmetric, Polar

Symmetric, Non-polar

If the molecule is:If the molecule is:

CovalentCovalent

The bonds are polar. If the shape is

The bonds are polar. If the shape is

Non-symmetricNon-symmetricSymmetricSymmetric

The molecule is polarThe molecule is polarThe molecule is non-polar

The molecule is non-polar

The molecule is non-polar

The molecule is non-polar

Ionic or two of the same element

Ionic or two of the same element