Molecular Geometry Worksheet



Name ______ _____ Period Date

Only one name per paper - 1 worksheet packet needs to be completely filled in for each student separately for individual lab grade. Models and pictures will receive group grade.

LAB: Dot Structures for Compounds and Molecular Model Building

Objectives: TEKS: 7(C) construct electron dot formulas to illustrate ionic and covalent bonds.

7(E) predict molecular structure for molecules with linear, trigonal planar, or tetrahedral electron pair geometries using Valence Shell Electron Pair Repulsion (VSEPR) theory.

Important Points to Consider:

*A compound will usually be ionic (electrons will be transferred) if it contains a metal and a nonmetal and covalent (electrons will be shared) if it contains a nonmetal with another nonmetal. Using the two element’s electronegativities, the type of bond between two atoms can be calculated by subtracting … a difference of greater than or equal to 1.7 will be ionic, between 1.7 and 0.3 will be polar covalent, less than or equal to 0.3 will be nonpolar covalent.

*The properties of molecules (covalent) depend not only on their molecular compositions and structure, but also on their shape. Molecular shape determines a compound’s state of matter, boiling point, freezing point, viscosity, volatility, surface tension and the nature of its reactions.

*The geometry of a small molecule can be predicted by examining the central atom and identifying the number of atoms bonded to it and the number of unshared electron pairs surrounding it.

*The shapes of molecules may be predicted by examining the central atom and identifying the number of atoms bonded to it and the number of unshared electron pairs surrounding it.

*Molecules made up of covalently bonded atoms can be classified as either polar or nonpolar. The geometry of the molecule determines whether it is polar or not.

Part 1 – Dot Structures Procedure:

1. In the first column of the chart on the next 3 pages, list if the bond is ionic, polar covalent or nonpolar covalent. (Refer to “Note Taking Guide: Episode 501” or book p. 191 & 262). Each person will fill out a separate packet today for the lab (ex: groups of 3 will have 3 packets to turn in).

2. Draw the dot structures in the second column. (Reminder: if there are more than two elements, carbon will go in the center. Otherwise the least electronegative atom will be in the center. Hydrogen is never the central atom.) Refer to book p. 174 for chart of metals, metalloids and nonmetals. Ionic compounds should be shown as two ions.

3. If the compound is covalent, list the number of electron pairs in the third and fourth columns. If the compound is ionic, put an “X” in the last three columns.

4. Obtain a piece of cardstock paper (one per group) and make a dot structure for an ionic compound made of metal and nonmetal elements. Do not use any listed in the chart on the next three pages – come up with your own, new example. Put the names of everyone in your group on the back of the card. On the front of the card, write the symbols for the ions, glue candies for the dots representing the valence electrons and write the exponent and the sign for the charge on the ions that make up your ionic compound.

Part 2 – Molecular Model Building Procedure:

5. Obtain a molecular model kit for your group. Check the contents to confirm that you have all pieces to the kit. Each kit has 1 blue (N), 20 yellow (H), 4 red (O), 3 green (Cl), 1 orange (Br), 1 purple (I) and 7 black (C) wooden spheres as well as about 15 pegs.

6. Build models for the molecules listed in the chart on the next two pages. (You will not build a model for the ionic compounds.)

7. In the last column, list the molecule’s geometric shape (linear, bent, tetrahedral, trigonal pyramidal, trigonal planar). Refer to book p. 256 & 257.

8. Using the model set, create a molecule not listed in the chart for the group.

9. On an index card, write (1) the elements used to make the molecule, (2) the molecule’s geometric shape and (3) the names of all students in your group.

10. If you have a phone or iPad, take a picture of the model along with the index card and e-mail to Mrs. Haag at haagk@ or raise your hand and have Mrs. Haag come to your group to take a picture of it with her iPad.

VSEPR Practice

For each of the following compounds, identify the bond type in the first column, draw the (Lewis) Dot Structure / Electron Dot Formula in the second column. Then, if the compound is covalent, identify the number of shared electrons pairs on the central atom, # of unshared pairs (lone pairs), and the correct the molecular shape. See book page 256.

|compound, |(lewis) dot structure/electron dot formula |# of shared |# of lone pairs |molecule’s shape (if covalent) |

|ionic or covalent | |electron pairs | | |

| | |on the central | | |

| | |atom | | |

|1. H2O |Example |2 |2 |bent |

| |[pic] | | | |

|polar covalent | | | | |

|2. NaCl |Example | | | |

| | | | | |

| |[pic] |X |X |X |

|ionic | | | | |

|3. CH4 | | | | |

| | | | | |

| | | | | |

|______________ | | | | |

|4. NH3 | | | | |

| | | | | |

| | | | | |

|______________ | | | | |

|compound, |(lewis) dot structure / electron dot formula |# of shared |# of lone pairs |molecule’s shape (if covalent) |

|ionic or covalent | |electron pairs | | |

| | |on the central | | |

| | |atom | | |

|5. BrI | | | | |

| | | | | |

|______________ | | | | |

|6. CaS | | | | |

| | | | | |

| | | | | |

|______________ | | | | |

|7. AlF3 | | | | |

| | | | | |

| | | | | |

|______________ | | | | |

|8. Cl2 | | | | |

| | | | | |

| | | | | |

|______________ | | | | |

|compound, |(lewis) dot structure / electron dot formula |# of shared |# of lone pairs |shape |

|ionic or covalent | |pairs | | |

|8. BCl3 |Note: Boron (B) is an exception to the octet rule. It does need to have 8 e- on its | | |Note: Determine shape without |

| |outer level to be stable | | |building model. |

|______________ | | | | |

|9. C2H6 |Note: In order to determine the number of electron groups and hence the molecular | | | |

| |shape, select one of the carbon atoms to be the central atom | | | |

| | | | | |

|______________ | | | | |

|10. HCl | | | | |

| | | | | |

| | | | | |

|______________ | | | | |

|11. Ba3N2 | | | | |

| | | | | |

| | | | | |

|______________ | | | | |

|12. CO2 | | | |12. Note: Determine shape |

| | | | |without building model. |

| | | | | |

|______________ | | | | |

-----------------------

(Does not apply to ionic compounds.)

Hint: chart of basic structures:

Does not apply to two atom molecules

Does not apply to two atom molecules

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download