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Chemical Bonding: Melting Point

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1. Consider the following data: expect a BeF2 molecule to be linear but an SF2 molecule to be angular.
Solubility in Water Melting
(kg/kg H2O, 25oC) Point (oC)
NaF 0.042 988
NaCl 0.357 801
NaBr 1.16 755
Nai 1.84 651

a) Explain the decreasing melting point from NaF to Nai.
b) Explain the increasing solubility in the same order.
c) Cesium fluoride has a melting point of 682oC and a solubility of 3.67 kg/kg H2O at 25oC. Explain the difference between the properties of CsF and NaF.

2. What test would determine whether a solid substance contains ionic bonds?

3. a) Explain why graphite is soft and has a high melting point.
b) Explain why diamond is hard and has a high melting point.
c) Why is diamond a poor conductor of an electric current and graphite a good conductor?

4. Answer the following questions using the information in the table.

Element Melting point (˚C) Boiling point (˚C) Molar volume at STP (L)
A -189 -186 22.4
B -100 -35 22.4
C -7 58 2.6 x 10-2
D 30 2240 1.2 x 10-2
E 44 280 1.7 x 10-2
F 660 2450 1.0 x 10-2
G 3410 5930 1.0 x 10-2

a) Which elements are likely to be metals?
b) Which elements are gases at STP?
c) Which element is most likely to be a non-metallic solid?
d) Which elements are likely to conduct well in the solid form?

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1. Consider the following data: expect a BeF2 molecule to be linear but an SF2 molecule to be angular.

Solubility in Water Melting
(kg/kg H2O, 25oC) Point (oC)
NaF 0.042 988
NaCl 0.357 801
NaBr 1.16 755
Nai 1.84 651

a) Explain the decreasing melting point from NaF to Nai.

When we move down the group, size f halogen atom increases, and therefore, the bond length of Na-X increase down the group(X is halogen). Therefore, we can see that bond length increases down the group and hence, bond is easy to break. Therefore, melting point decreases down the group from NaF to NaI.

b) Explain the increasing solubility in the same order.

When we move down from NaF to NaI, the ionic character of the molecule increase that is NaI is most ionic. Therefore, due to ...

Solution Summary

This solution answers several chemistry questions, addressing melting point, solubility, ionic bonds and STP.

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See Also This Related BrainMass Solution

Covalent and Ionic Bonding

Research the answers to the following questions on the internet and write your answers in your own words. For each answer, include the address of the web site (or title and author of a book or article) that you used to help you answer the question.

1. Which type of compound usually has higher melting points: ionic compounds or covalent compounds? What is the reason for this difference in melting points? (3 points)

2. Do ionic compounds conduct electricity as: (3 points)
1. Solids?
2. Liquids?
3. Aqueous solutions (when the ionic compounds are dissolved in water)?

3. Do covalent compounds conduct electricity as: (3 points)
1. Solids?
2. Liquids?
3. Aqueous solutions (when the covalent compounds are dissolved in water)?

4. Explain the differences between ionic and covalent bonding that account for the differences in their melting points.

5. In order to conduct an electrical current, a substance must have charged particle s (ions or electrons) that are free-moving (able to move about throughout the sample).

6. Why do you think ionic compounds are not able to conduct electricity as solids, even though they can as liquids and in solution?

7. why do you think pure (distilled) water does not conduct electricity but tap water usually does?

Part II

Molecular Model for your models of H2O, NH3, CH4, and CO2.
1. Use the information from the lesson to determine the answers to the questions below.
Conclusion:
For each of your molecules, answer the following questions:
1. Determine the electronegativity between the atoms of each molecule.
2. Identify the bond as either ionic or covalent.
3. State whether the molecule is polar or non polar.
4. Identify the structure as having hydrogen bonding, dipole-dipole moments or London dispersion forces (LDF).

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