8.1 Chemical Bonding

Purpose

To construct 3-dimensional models which accurately represent molecular structure

To predict the shapes of small molecules

To predict the polarity (dipole moment) of molecules based on their models

Materials

Molymod molecular modeling kits DON’T MIX THEM UP!!!!!

CH4, CCl4, CHCl3, CH2Cl2, NH4+, NH3, NF3, H2O, OF2, CO2, N2, H2, HCl

C- 4 hole, N- 3 or 4 hole, O- 2 or 4 hole, H, Cl, F, Br- 1 hole

Single bond-short stick, double bond- 2 long sticks, triple bond- 3 long sticks

Inventory list: 1 Black, 2 Blue, 4 Red, 2 Green, 2 Silver, 1 Yellow, 1 Purple, 1 Tan, minimum 6 Short Gray Bonds, min 3 Short Purple Bonds, min 4 Long Flexible Bonds

Procedure

  1. Read through the entire procedure, data analysis, and conclusion sections to be sure of the expectations of this exercise.
  2. Fold the paper lengthwise into 3 columns. You may use more than 1 sheet.
  3. In the first column, write the formulas listed above.
  4. In the second column, draw a Lewis Dot structure for each of the molecules. Be sure to show all bonds and lone electron pairs.
  5. Use the Molymod kit to construct a model of each molecule taking note of the symmetric distribution of bonds and lone pairs of electrons about the central atom. Make a 3-dimensional sketch of the Molymod model for each formula.
  6. Use the Lewis Dot structures and the Molymod models to analyze the overall molecular polarity. If the molecule would not be expected to exhibit polarity, write “Non Polar” beneath the Lewis Dot structure.
  7. Feeling Lucky? Identify the remaining molecules that would be expected to exhibit a dipole and indicate the direction with the dipole arrow (+à).
  8. Double check the materials inventory list of the kits. Advise the teacher as to extra or missing pieces.

Data Presentation

  1. Submit the tri-folded papers showing the formula, Lewis Dot, and 3-D drawings.

Data Analysis

  1. Do all of these models satisfy the octet rule?
  2. Compare the flexibility of a single bond to that of a double and triple bond.
  3. What characteristic suggests a non-polar molecule?
  4. Summarize the two main factors that contribute to a molecule exhibiting polarity.

Conclusions

  1. Explain if the molecular formula alone be used to predict the polarity of a molecule?
  2. Propose an explanation as to why the bonds about the central atom generally exhibit a large degree of symmetry. Look at CH4 and CCl4 for clues.
  3. Propose a hypothesis for why NH3 does not fit into a flat planar triangle design.

Periodic Properties

The object of this lesson is to use the periodic properties of the elements to fill in the following chart. The code letters A to Z have been assigned to the first 26 representative elements in the periodic table. The code letters do not represent certain chemical symbols, that is, C may not be carbon, nor have the letters been assigned in alphabetical order.

These letters are presented in families, and your task is to arrange these letters in the proper location in the periodic chart. To do this, use the clues given pertaining to certain members of each family. The numbers in each square in the table are the atomic numbers of the elements.

The best way to start is to use the clues to find in which group each family belongs, and then to arrange the elements within the family using the other clues. The following elements belong together in families: WXYZ, STUV, ABC, DEF, GHI, JKL, MNO, and PQR.

Clues:

1. Element M is not the largest in its group and will react with element O to form both MO3 and MO2.

2. Elements L & E are from the same period.

3. The radius of atoms of element P are smaller than the atoms of element R.

4. Element T has the lowest ionization potential in its group (family).

5. Element W is more reactive than element A and element A is more reactive than element D. All three elements are in the same series (period or row).

6. The radius of atoms of element H are smaller than atoms of element I.

7. Element B is the least reactive alkaline earth element.

8. The Lewis dot notation for element K is shown below:

9. When element K and L react, L has a positive oxidation state (charge).

10. Element Q is the most electronegative element.

11. The atomic number of element V is one more than element P.

12. Element J is the most non-metallic element in its group.

13. Elements C & N are from the same period and react to form CN.

14. The oxidation state (charge) of element O is 2- in almost all compounds except when bonded to atoms of element Q

15. Element Z is the most reactive metal in its period.

16. The atomic number of Z is 16 more than the atomic number of Y.

17. Element E reacts with element P to form EP3.

18. Element U is the smallest element in its period, but not in its group.

19. Element G has the highest ionization potential in its group.

The following Periodic Table shows only the Group A elements. Note that the atomic numbers jump from 20 to 31 in the fourth period. This is because elements 21 through 30, the transition elements, belong to the B Groups.

I A / VIII A
1 / II A / III A / IV A / V A / VI A / VII A / 2
3 / 4 / 5 / 6 / 7 / 8 / 9 / 10
11 / 12 / 13 / 14 / 15 / 16 / 17 / 18
19 / 20 / 31 / 32 / 33 / 34 / 35 / 36