Polarity and Molecule Shape Lab

Statement of the Problem:

• Construct Models of Molecules
• Determine Molecule Shapes
• Predict Polarity of Molecules

1. Background Information:
• The most common type of bond between two atoms is a covalent bond. A covalent bond is formed when two atoms share a pair of electrons. If both atoms have the same electronegativity or tendency to attract electrons the bond is nonpolar covalent. When atoms have different electronegativity the electrons are attracted to the atom with the higher electronegativity. The bond that forms is a polar covalent
• Molecules made up of covalently bonded atoms may themselves be polar or nonpolar. If the polar bonds are symmetrical around the central atom, the bonds offset each other and the molecule is nonpolar. If the polar bonds are not symmetrical, the electrons will be pulled to one end of the molecules and the molecule will be polar. (If the polar end is "sticking out" it will be a polar molecule)
• Many physical properties of matter are the result of the shape and polarity of molecules. Water, for example, has unusual properties that can be explained by the shape of its molecule and the distribution of charge on the molecule.

Hypothesis:

• The polarity of molecules that we build will show nonpolar/polar characteristics depending on electronegativity.

Materials:

• Molecule Model Kit

Procedure:

1. Build a model for each of the molecules listed on the date table on the back of the page given us.
2. Draw the 3D structure of each molecule in table 1. Use solid lines to represent bonds in the plane of the paper, dashed lines for bonds that point back from the plane on the paper, and wedged lines for bonds that point out from the plane of the paper toward the viewer.
3. Note the shape of each molecule in third column of table 1, the bond angles in column 4, whether or not they will be polar in column 5, and whether or not they exhibit resonance structure in column 6.

Results:

Lewis Structure- -Model- -Shape- -Bond Angle- -Polarity- -Resonance-

CH4

-[Model Unavailable]- -Tetrahedral- 109.5 degrees- -No- -No-

BF3

-Pyramidal- -90-109.5 degrees- -Yes- -No-

C3H8

-Tetrahedral- -109.5 degrees- -No- -No-

H20

-Angular- -90-109.5 degrees- -Yes- -No-

Si2H6

-Tetrahedral- -109.5 degrees- -No- -No-

HF

-Linear- -180 degrees- -Yes- -No-

CH3NH2

-Terahedral/pyramidal- -109.5/90-109.5 degrees- -No/Yes- -No/No

H202

-Angular- -90/109.5 degrees- -Yes- -No-

N2

-Linear- -180 degrees- -No- -No-

SeF4

-Tetrahedral- -109.5 degrees- -Yes- -No-

C2H4

-Pyramidal- -90/109.5 degrees- -No- -No-

SiH20

-Trigonal Planar- -120 degrees- -Yes- -No-

IF3

-Pyramidal- -90/109.5 degrees- -Yes- -No-

SF6

-Square Pyramidal- -90 degrees- -Yes- -No-

CO2

-Linear- -180 degrees- -Yes- -No-

SO3 [-2]

-SeeSaw- -120/90 degrees- -Yes- -Yes-


Conclusion:

• Each atom followed the octet rule and the shapes of the adjacent molecules corresponded with this action.
  

Questions and Answers:

Q- Explain how water's Shape causes it to be polar.
A- The negative and the positive elements are on the opposite ends of the molecule thus causing it to be polar.

Q- Describe how water's properties would be different if the molecules were linear instead of bent.
A- It would "just float away" as Mr. Howell said, respectively.

Q- Based on the results of this experiment, list the molecules that would be water-soluble.
A- H20, HF, C2H4