Molecular Geometry and VSEPR Theory Worksheet

Chem 06.100 Lab: Molecular Geometry and VSEPR TheoryThere is no lab notebook preparation or quiz for this experiment. The lab report for this experiment is this completed packet in
addition to the post lab questions (End of the document). Print or redraw the questions on a blank sheet of paper. Then complete
this packet by the due date.
INTRODUCTION
Most molecules in chemistry obey the octet rule. Their Lewis- structures are straightforward. To draw the Lewis structure of a molecule
obeying the octet rule, eight electrons on each atom (except hydrogen and a few others) are arranged in four pairs. Each pair either
participates in a covalent bond or is present as a lone pair. Some molecules have an odd number of valence electrons or may have an
expanded octet.
According to the Valence Shell Electron Pair Repulsion (VSEPR) Theory, areas of high electron density are arranged as far apart from
each other as possible. The repulsion of electron pairs determines the geometry or molecular structure of the molecule. The molecular
shape is determined by the positions of the atoms in a molecule, not the positions of the electrons.
Objective: To predict structure and polarity of a compound based on its Lewis Dot structure and VSEPR Theory.
Number of
Electron domains
2
3
4
5
6
Number of Nonbonding electron pairs
0
0
1
0
1
2
0
1
2
3
0
1
2
Electron Domain
Geometry
Linear
Trigonal Planar
Tetrahedral
Trigonal
bipyramidal
Octahedral
Molecular Geometry
Approximate Bond angles
Linear
Trigonal Planar
Bent (V shaped)
Tetrahedral
Trigonal pyramidal
Bent (V shaped)
Trigonal bipyramidal
Seesaw
T-shaped
Linear
Octahedral
Square pyramidal
Square planar
180 °
120 °
95 °
109.5 °
< 109.5 ° 104.5 ° 90 °(ax) & 120°(eq) < 90° (ax) < 120° (eq) < 90 ° (ax) 180 ° 90 ° < 90 ° 90 ° Page 1 of 7 Chem 06.100 Lab: Molecular Geometry and VSEPR Theory Knowing the geometry of a molecule allows one to predict whether it is polar or nonpolar. Molecular polarity can also be determined by subtracting the electronegativity values of the individual atoms in a bond. A bond that is polar has a positive and negative end. A bond between two identical atoms or two atoms with similar electronegativities is nonpolar. The symmetry of a molecule with polar bonds determines the molecular polarity. 15 Molecules, 6 points each. Procedure: Complete the table and determine the molecular geometry of the molecules below. Some marshmallows and toothpicks (or the like) can be used as a molecular modeling set. If you have access to a molecular modeling set, build the molecule. then complete the chart. This activity is best accomplished by moving from left to right and filling in columns 1-8 for each molecule, then moving downwards in the table. Column 1: Determine the total number of valence electrons in the compound, molecule or ion, and write the number in the space provided. Column 2: Draw the Lewis electron dot structure. Use —to indicate bonds. Show ALL lone electron pairs with ●●. Label bonding pairs and Label Lone pairs. Column 3 and 4: Using VSEPR, identify electron domain geometry and molecular geometry of the molecule, respectively, around each central atom. If there is no central atom, write “no central atom” (ex: NaCl has no central atom). Column 5: If using a model kit, build the model using the model kits & diagram what you build. Identify Bond Angles present. Column 6: Using Molecular Shape Designation AXmEn write the proper formula of the compound Column 7: Check your molecule with Formal charge used to check if Lewis is correct FC each element = valence e- - (# of bonds + dots). Indicate FC for each individual atom type Column 8: Indicate whether the compound is primarily polar or nonpolar based upon VSEPR Molecular shape and the presence or lack of an overall dipole. Page 2 of 7 Chem 06.100 Lab: Molecular Geometry and VSEPR Theory 1 Species & No. Valence eˉ 2 3 4 5 Lewis Structure Electron Domain Geometry Molecular Geometry Perspective (3D) Drawing w/ labeled Bond Angles 6 Molecular Shape Designation AXmEn CH4 – __8__ e AX4 7 8 Formal Charge on Each Atom Type Polar or Non-polar? C = 0, H=0 Non-polar NH3 __ __ e– NO3– __ __ e– H2O __ __ e– Page 3 of 7 Chem 06.100 Lab: Molecular Geometry and VSEPR Theory 1 Species & No. Valence eˉ 2 3 4 5 Lewis Structure Electron Domain Geometry Molecular Geometry Perspective (3D) Drawing w/ labeled Bond Angles 6 Molecular Shape Designation AXmEn 7 8 Formal Charge on Each Atom Type Polar or Non-polar? NH4+ _ _ _ e– PF3 _ _ _ e– PF5 _ _ __ e– H2S _ _ _ e– Page 4 of 7 Chem 06.100 Lab: Molecular Geometry and VSEPR Theory 1 Species & No. Valence eˉ 2 3 4 5 Lewis Structure Electron Domain Geometry Molecular Geometry Perspective (3D) Drawing w/ labeled Bond Angles 6 Molecular Shape Designation AXmEn 7 8 Formal Charge on Each Atom Type Polar or Non-polar? SF6 _ _ _ e– SeF4 _ _ e– XeF2 __ _ e– CO2 __ _ e– Page 5 of 7 Chem 06.100 Lab: Molecular Geometry and VSEPR Theory 1 Species & No. Valence eˉ 2 3 4 5 Lewis Structure Electron Domain Geometry Molecular Geometry Perspective (3D) Drawing w/ labeled Bond Angles 6 Molecular Shape Designation AXmEn 7 8 Formal Charge on Each Atom Type Polar or Non-polar? BrF4+ __ _ e– SF4 __ _ e– XeF4 __ _ e– BrF3 _ _ _ e– Page 6 of 7 Chem 06.100 Lab: Molecular Geometry and VSEPR Theory Post Lab Questions (10 Points). Answer the following question on this sheet Use Lewis Structures and VSEPR theory to explain each of the following: (a) (2 pts.) The bond length between the two carbon atoms is shorter in C2H4 than in C2H6. (b) (2 pts.) The H–N–H bond angle in NH3 is 107.5°. (c) (3 pts.) All the bonds in SO3 are identical in length and shorter than a single S–O bond. (d) (3 pts.) The I3–ion is linear. Page 7 of 7