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CP Sci 9- 1st Sem.

Gen Chem - 1st Sem.

Polarity:

Objectives:

    1.    State the two factors that determine polarity of a molecule.

    2.    Explain how the structure of a molecule helps determine its properties.

Key Terms:

    dipole

Resources:

Notes: (8-2)

Just like a magnet, molecules can have distinct associated with opposite ends of the molecules.  This is called dipole (2 poles) and describes a polar molecule.  Polar molecules have certain properties that even greater support the idea of dipole.

bulletpolar molecules will align with the charge in an electric field
bulletpolar molecules will be attracted or repelled by a charged rod or magnetic field

Determining polarity requires looking at the type of bond as well as the shape of the molecule.  Examine the following molecules to see how to determine the polarity of a molecule.

bulletMolecules consisting of a single element are all nonpolar. 

        O2, O3, H2, N2, Diamond, ...

(www.cchem.berkeley.edu/.../ discussion/week15/1-2a.GIF)

bulletIf the electronegativities are dissimilar on the opposite sides of a molecule chances are that the molecule is polar.  Look at formaldehyde.

(web.centre.edu/~muzyka/che11/ 131lab/formaldehyde.gif)

        The shape is trigonal planar with oxygen being much more electronegative than the hydrogen.  This demonstrates the dipole very well with oxygen being the negative pole and the hydrogens being the positive pole.

bulletMolecules that form mirror images (symmetrical) of themselves are nonpolar even though their bonds appear polar.  Look at Carbon dioxide, methane, and boron triflouride.

            

    All three contain polar bonds but are nonpolar because the bonds are all pulled in equal and opposite directions.

bulletMolecules that contain unpaired electrons are usually polar.  Look at water and ammonia.

 

    

    The hydrogens represent the positive pole and the unpaired electrons are the negative pole.

Large Molecules:

Large molecules (macromolecules) will often have many polar and nonpolar regions.  The polarity of these regions help the molecules determine the shape (confirmation) and the function of the molecules.  

Protein:

Lysozyme, one of the primary constitutent proteins in albumen

(paulmessier.com/PM/ images/protein.jpg)

Lipid:

   

(abe.www.ecn.purdue.edu/ABE/Research/ research95/lipid.gif)

 

 

 

 

 

 

 

 

Last modified: September 05, 2004