Lab Activity: Molecular Model Building

Part I The first set of molecules we will examine contain only two atoms. For each of the following, draw the Lewis structure, identify the molecular shape and the polarity of the molecule.

Molecular Shape Polarity Species Draw the Lewis Dot Structure (linear, bent, trigonal planar, trigonal (polar or nonpolar?) pyramidal, tetrahedral?)

Br2

HBr

Conclusions:

If only two atoms are bonded, the molecular shape will always be ______.

If the two bonded atoms are identical, the molecule is ______(polar or nonpolar).

If the two atoms are different, the molecule is ______(polar or nonpolar). The atom with the ______(greater, smaller) electronegativity will be partially negative (-).

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Part II (table of molecules starts on page 3)

1. The following molecules contain more than 2 atoms. Draw the Lewis structure for each of them. 2. Make a model of the molecule. Use the short gray plastic connecting rods for single bonds and lone pairs of electrons. Use the longer flexible connecting rods for double and triple bonds. (2 for a double bond; 3 for a triple bond) Use the following colored spheres: C, Si = Black N, P, As = Blue H = White O, S = Red Cl, Br, I = use purple or orange If the "red" sphere is the central atom, you won't be able to see the lone pairs of electrons. If you like, you can use a black sphere in these cases. 3. The electron geometry is determined by the number of electron groups on the central atom. (Hint: Look at the arrangement of the connecting rods.) 4 groups result in a tetrahedral arrangement of the electron groups. 3 groups result in a trigonal planar arrangement of the electron groups. 2 groups result in a linear arrangement of the electron groups.

4. Determine the molecular shape of the molecule. While the lone pairs of electrons influence the molecular shape, the arrangement of the ATOMS is used to describe the molecular shape. DO NOT USE ANY ABBREVIATIONS IN YOUR ANSWERS!

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Possible Shapes for Molecules with 4 electron groups around the central atom (bond angles near 109.5o)

Molecular Shape 3D sketch and Lewis structure

Tetrahedral A four sided figure. Each side is an equilateral triangle.

Trigonal pyramidal A four sided figure. Three sides are isosceles triangles. They are sitting on an equilateral triangular base.

Bent A nonlinear arrangement of atoms.

Possible Shapes for Molecules with 3 electron groups around the central atom (bond angles near 120o)

Molecular Shape 3D sketch and Lewis structure

Trigonal Planar A flat molecule. The atoms bonded to the central atom form an equilateral triangle. The central atom sits in the center of the triangle.

Bent A nonlinear arrangement of atoms.

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Electron Geometry Molecular Shape (linear, trigonal # of Electron (linear, bent, trigonal Polarity (*) Species Lewis Dot Structure planar, tetrahedral?) Groups planar, trigonal (polar or nonpolar?) Include bond pyramidal, tetrahedral?) angles!

CBr 4

CHBr3

OF 2

H2S

(*) Your instructor may specify which molecules to work on regarding this question. Page 4 of 6

SCl2

PCl3

CS2

HCN

COCl2

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This page contains polyatomic ions. They have gained or lost valence electrons to become charged.

NO – 2

NH + 4

2– CO3

- 2- **Nitrite (NO2 ) and carbonate (CO3 ) have resonance structures – different but equivalent Lewis structures. Draw at least two resonance structures for these polyatomic ions.

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