Covalent Bonding and Molecular Models Lab

Purpose: To build models of various molecules based on a set of rules for how atoms covalently bond.

Materials: 1 molecular model kit per team of 2 students.

Background Information:

ù The 3-dimensional shapes of molecules can be envisioned with the use of molecular models.

ù Before you can assemble an accurate model of a molecule you need to know what type of atoms make up the molecule and their relative numbers. For example, the chemical formula of water, H2O, tells us that each and every water molecule is made of two hydrogen atoms and one oxygen atom.

ù The second thing you need to know is how the atoms of the molecule fit together. Through chemistry we find that there are specific ways in which different atoms form covalent bonds:

! Hydrogen atoms have one valence electron and can only form one covalent bond.

! Carbon atoms have four valence electrons and form four covalent bonds.

! Nitrogen atoms have five valence electrons, but only three unpaired electrons. Nitrogen atoms usually form three covalent bonds.

! Oxygen atoms have six valence electrons, but only two unpaired electrons. Oxygen atoms form two covalent bonds.

! Fluorine atoms have seven valence electrons, but only one unpaired electron. Fluorine atoms can only form one covalent bond.

Molecular Models:

The molecular modeling kits represent different atoms with different colors and different bonding abilities. ù Hydrogen atoms are represented by pieces and have a place for one covalent bond. ù Carbon atoms are represented by BLACK pieces and have a place for four covalent bonds. ù Nitrogen atoms are represented by BLUE pieces and have a place for three covalent bonds. ù Oxygen atoms are represented by RED pieces and have a place for two covalent bonds. ù Fluorine atoms are represented by GREEN pieces and have a place for one covalent bond.

To build a molecule, the pieces representing atoms are connected by plastic sticks: ù Short plastic sticks represent single covalent bonds between atoms. In some instances, it may be necessary to form multiple covalent bonds between atoms. ù The long, flexible plastic sticks represent multiple covalent bonds between atoms and are used to make double or triple covalent bonds. ù Covalent molecules can often be put together in more than one way. ù Compounds with the same formula, but different structures or shapes are called isomers.

*****Please turn the page for the Procedure and “rules” for determining the correct structure.*****

The correct structure for a molecule has been built when each atom in the molecule has the appropriate number of bonds.

This is a hands-on, “learn as you go” activity. Have fun!

Procedure: 1. Obtain one molecular model kit per team of two students. Check to make sure the kit is complete prior to starting. 2. Record your molecular model Kit # on your lab record sheet by your name. 3. Record the color, Lewis dot diagram, and number of bonds each atom can form in Table 1. 4. Build each of the molecules listed in the table below. None of these molecules form ring structures. 5. Complete Table 2 on your lab record sheet by drawing an accurate representation of each structure you have made. Draw in ALL lone pairs of electrons as well (to complete duets/octets/sextets, etc.) 6. Be sure to follow the SPECIFIC instructions for molecules #14 & 15. 7. Answer all 8 of the conclusion questions on the provided lab record sheet. 8. After checking to make sure all the pieces are there, return the molecular model kit for your instructor to check over.

Rules: 1. All holes in each sphere used must be filled with a stick (bond). 2. All sticks (bonds) must be attached to a sphere (atom). (The only exception is that the nitrogen atoms should have three holes (the fourth hole should be filled with something/covered with tape so please ignore it.) 3. There will be no structures in a ring (cyclic shaped). This means that you will not have 3 atoms in a triangular shape, nor 4 atoms in a square shape, 5 atoms in a pentagon, etc. 4. For #14, the oxygen atom is bonded to carbon and hydrogen. 5. For #15, both oxygen atoms are bonded to the same carbon atom. There is only a single bond between the carbon atoms.

Molecules to build:

1. Hydrogen, H2 7. Carbon dioxide, CO2 13. Difluoroethane, C2H4F2 2. Fluorine, F2 8. Methane, CH4 14. Ethanol, C2H6O 3. Hydrofluoric 9. Water, H2O 15. Ethanioc acid, acid, HF C2H4O2 4. Oxygen, O2 10. Hydrogen peroxide, H2O2 16. Ethene, C2H4 5.Nitrogen, N2 11. Difluoromethane, CH2F2 17. Ethyne, C2H2 6. Ammonia,NH3 12. Ethane, C2H6 18. Propene, C3H6 19. Fluoropropane, C3H7F