1) H2 2) O2 3) N2. 4) HCl 5) H2O CHEMISTRY LAB MODELING COVALENT MOLECULES BOND TYPE(S) LEWIS STRUCTURE POLARITY OF MOLECULE ELECTRONIC SHAPE

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1 CHEMISTRY LAB MODELING COVALENT S NAME: PER: FORMULA MOLECULAR 1) H2 hydrogen gas 2) O2 oxygen gas 3) N2 nitrogen gas 4) HCl hydrochloric acid 5) H2O dihydrogen oxide

2 FORMULA MOLECULAR 6) CO2 carbon dioxide 7) NH3 ammonia nitrogen trihydride 8) CCl4 carbon tetrachloride 9) CH3Cl methyl chloride 10) CH3OH methanol

3 FORMULA MOLECULAR 11) IF5 iodine pentafluoride 12) SCl6 sulfur hexachloride 13) PBr5 phosphorus pentabromide 14) AsI3 arsenic triodide 15) SeF4 selenium tetrafluoride

4 BUILDING MODELS OF COVALENT S PURPOSE: To construct models of covalent substances in order to show how their shapes and structure determine their polarity. PROCEDURE: Complete the data table by: 1) Drawing the Lewis structure of the molecule. 2) Determine the bond type (polar covalent, nonpolar covalent) by calculating the electronegativity difference between the elements. 3) Make a model of each substance. Have the instructor check off that the model is correct before continuing. 4) Make a sketch of the model and determine the molecular shape of the substance. 5) Determine the polarity of the molecule. MATERIAL: Obtain a model set and colored pencils. Each model set includes the following (the element(s) the different colors represent are given as well) 12 bonds 8 white (small 1 prong): hydrogen 6 green or white (4 prongs): halogens 3 red: oxygen 2 blue: nitrogen 1 yellow: sulfur 3 black: carbon 1 purple (5 prongs): phosphorus, iodine, sulfur or selenium 1 silver (6 prongs): iodine, sulfur or noble gas BACKGROUND INFO: A covalent bond consists of a pair of shared electrons. Such a pair of electrons is shared equally between identical atoms (or two different atoms with the same electronegativity) producing a bond which is pure (nonpolar) covalent. The unequal sharing of the electron pair between two different atoms produces a bond which is more or less polar. The polarity of the bond may be described in terms of its percentage of ionic character. This depends on the electronegativity difference between the two bonded atoms. The electronegativity of an atom (element) is a measure of its tendency to attract the electrons forming a bond between it and another atom. Molecules of covalent substances may be nonpolar or polar. A diatomic molecule of an elementary gas is nonpolar. A diatomic molecule of a compound is linear and may be polar. More complex compounds have molecules which may be polar or nonpolar depending the symmetry of the bonds to the central atom and consequently on the symmetry of the molecular structure. A molecular structure, even though its bonds are polar bonds, will be nonpolar if the bonds are arranged evenly about the central atom. When the arrangement of the polar bonds is unsymmetrical, the resultant molecule is polar and is called a dipole. Representative molecules may be bent (nonlinear) or trigonal pyramidal. A dipole acts as if it has a positively charged portion and a negatively charged portion equal in magnitude of charge(s) and separated by some distance. When constructing the models in this lab, any prong not involved in the bonding can be considered a lone pair of electrons.

5 NAME: PER: 1) Calculate the electronegativity difference and bond type (nonpolar covalent, polar covalent, ionic) for each of the following bonds. electronegativity difference bond type a) H O b) H N c) H Cl d) Br Cl e) H S f) H C g) Cl Cl h) C O i) K Br j) Na O 2) Classify each of the following as an ionic crystal, polar molecule or a nonpolar molecule. a) Br2 b) MgCl2 c) CCl4 d) HI e) CO2 f) H2O g) N2 3) Both water and carbon dioxide are tri-atomic molecules. Explain why one of these is polar and the other is nonpolar.