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Building Three Dimensional Molecules Name: Date: Introduction: A single covalent bond is formed when 2 atoms share a pair of electrons. Each atom provides one of the electrons of the pair. If the two atoms are identical, the bond is said to be nonpolar covalent. If the atoms are different, one exerts a greater attractive force on the electrons and the bond is polar covalent. More than one pair of electrons can be shared. This results in a double or triple bond. A group of atoms held together by covalent bonds is called a molecule. Molecules can be either polar or nonpolar. If bonds are nonpolar, the molecule is nonpolar. If bonds are polar, molecules ean still be nonpolar if the charge distribution throughout the molecule is symmetrical. A molecule’s symmetry depends on its shape, that is the positions in space of the atoms making up the molecule. Some possible shapes are linear, angular (bent), pyramidal, and tetrahedral. Although we represent molecules on paper as being 2 dimensional for convenience, they are actually 3 dimensional. By building molecular models, chemists come to understand the bonding, shapes and polarity of even the most complex molecules. Purpose: Build 3 dimensional models of some simple covalent molecules. Predict their shapes and polarities from knowledge of bonds and molecule polarity rules. Procedure: 1) Obtain a molecular model building set. Study the color code identifying the different kinds of atoms. a) Hydrogen= yellow b) Halogens=green c) Carbon=black d) Oxygen; Sulfur= red e) Nitrogen=blue 2) Observe the number of bonding sites: a} One Bonding Site: Hydrogen, Fluorine, Chlorine, Bromine and Jodine b) Two Bonding Sites: Oxygen and Sulfur c) Three Bonding Sites: Nitrogen d) Four Bonding Sites: Carbon 3) Construct models of the following molecules and have your teacher sign off on the finished model before disassembly. 4) Fill in the data table with the Lewis Structure, Bond Angle and Molecular Shape, and three dimensional drawing. Remember, in three dimensional drawings, a) dashed lines indicate the atom is pointing away from you. b) solid lines indicate the atom is in the plane of the paper. ¢) bold lines indicate the atom is pointing toward you. 48 
