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Polarity, bond dissociation energy of molecules

Detailed answers & explanations would be great. If hand written please do not write in cursive for I have trouble reading it.

1. Using Lewis (electron-dot) structures, explain why the ClF3 molecule is polar and the BF3 molecule is not polar.

2. For the following questions refer to the following diatomic species.
(A) Li2
(B) B2
(C) N2
(D) O2
(E) F2
a) Which has the largest bond-dissociation energy?
b) Which has a bond order of 2?
c) Which contains 1 stigma (s) and 2 pi (p) bonds?

3. On the basis of bonding principles, predict whether each of the following compounds exists. In each case explain your prediction.
a) NF5
b) AsF5

4. A mixture of 6gm of O2 (g) and 9gm CH4(g) is placed in a 15L vessel at 0 degreed Celsius. What is the partial pressure of each gas and what is the total pressure in the vessel?

5. Describe the intermolecular forces that must be overcome to convert these substances from a liquid to a gas.
a) SO2
c) H2S

6. Amorphous Silica, SiO2, has a density of about 2.2gm/cc whereas the density of crystalline quartz is 2.65 gm/cc. Account for the differences in density.

7. What are face centered and body centered crystal lattice?

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Solution Preview

1. For ClF_3, the total number of electrons = 28. There are 3 ligands = 8 x 3 = 24 electrons. The remaining 4 electrons should be 2 lone pairs on the central atom. Hence the molecule should be T-shaped.

See attached

The dipoles of the F's aligned vertically opposite to each other will cancel leaving the dipole of the horizontal Cl-F bond intact. Hence there will be net residual dipole moment making the compound polar.

Similarly for BF_3, the Lewis structure can be drawn as being trigonal planar as there are a total of 24 electrons.

See attached

The net dipole of any two B-F bonds will be equally and opposite in strength to the other B-F bond. Hence the dipoles will cancel leaving no residual dipole moment and hence making the compound non-polar.

2. The number of bonds between each atom decides the strength of the bond. Triple bonds will be stronger than double bonds in general. Of all the species, only N_2 has a triple bond. Hence it will have the ...

Solution Summary

A number of problems based on atomic theory are solved.