Building Models of Molecules Lab Answers to Post-Lab questions To download molecule imaging software go to http://phet.colorado.edu/en/simulations/category/ch emistry Building Molecules Post-Lab Review 1. Compare your models to the Lewis Dot Diagrams that you drew in the data table. How are the similar? How are they different? Answer: Both the models and the Lewis Dot Diagrams show how the different atoms are connected together and which atoms have lone pairs of electrons. The difference is that the models are 3D and the Lewis dot diagrams are flat. The 3D model shows the 3D shape of the molecules. Building Molecules Post-Lab Review 2. Which molecules contained at least one double bond? How did you know? A: Carbon dioxide, formaldehyde, sulfur dioxide, and ozone had at least 1 double bond. This was necessary to have all the atoms meet the octet rule. 3. Which molecules contained at least one triple bond? How did you know? A: Nitrogen gas and hydrogen cyanide had at least one triple bond. Both of these had a nitrogen bonded to only one other atom. Nitrogen needs three bonds to meet the octet rule. This required a triple bond. 4. Which molecules contained all single bonds? How did you know? A: Water, difluoromethane, and phosphorous trichloride had all single bonds. All the atoms connected to the central atom in these molecules only needed to share one to meet the octet rule or duet rule for hydrogen. Building Molecules Post-Lab Review 5. Group together molecules that have the same number of atoms coming off the central atom. Do these molecules have the same molecular shape? A: Carbon dioxide, water, hydrogen cyanide, sulfur dioxide, and ozone all have two atoms coming off the central atom. Some are bent in shape and some are linear. Formaldehyde and Phosphorous trichloride have three atoms coming off the central atom. The first is trigonal planar and the second is trigonal pyramidal. 6. In the models, why are atoms and lone pairs of electrons positioned as far apart as possible? A: The atoms and lone pairs are spread out as much as possible so that electrons flying around all the atoms can be as far apart as possible. They want to be far apart because like charges repel and all electrons are negatively charged. Building Molecules Post-Lab Review 7. If you only look at the chemical formula of a molecule, can you determine its shape? Why or why not? A: If the molecule is made of two atoms, then the shape is linear. If there are more than two atoms, then the formula does not determine the shape. The location of lone pairs of electrons contributes to the shape. For example CO2 and SO2 have similar formulas but different shapes. 8. By looking at the geometry of a molecule, how can you determine if it is polar or nonpolar? A: The molecule is nonpolar if atoms and lone pairs are distributed evenly around the central atom. If there are different atoms or different amounts of lone pairs around the central atom, it is polar because the different atoms have different electronegativities.