Intermolecular Forces and Chemical Properties.notebook
March 26, 2015
Intermolecular Forces and Chemical Properties
Melting & Boiling Points
The stronger the intermolecular forces, the higher the boiling/melting point of the substance because it takes more energy to separate molecules that have high attraction for each other.
Oct 7­8:07 AM
How do we compare the strength of IMFs?
H­bonding
(polar with H­N,O,F)
Dipole­dipole
(polar)
Strength depends on ∆EN
LDF
(nonpolar)
Strength depends on # e­s
Oct 7­9:09 AM
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Intermolecular Forces and Chemical Properties.notebook
March 26, 2015
Example 1 : Would F2 or Cl2 have a higher boiling point? Explain your answer.
Oct 7­9:22 AM
Example 2: Predict whether CH4 or CH3Cl would have a higher melting point. Explain your answer.
Oct 7­9:24 AM
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Intermolecular Forces and Chemical Properties.notebook
March 26, 2015
Example 3: Br2 and ICl each have 70 e­. Which one has the higher melting point?
Oct 7­9:25 AM
Solubility
In order for a substance to dissolve, particles of the solute (what is being dissolved) must be able to overcome the attraction the between particles of the solvent (what is doing the dissolving).
Oct 7­9:28 AM
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Intermolecular Forces and Chemical Properties.notebook
March 26, 2015
Example 1: Why does ammonia dissolve in water?
These are both polar molecules with H­bonding attractions.
The poles of the water molecules are attracted to the poles of the ammonia molecules allowing the water molecules to surround the ammonia molecules creating a solution.
Oct 7­9:31 AM
Example 2: Why doesn’t CCl4 dissolve in water?
Answer: CCl4 is a nonpolar molecule. Water molecules are highly attracted to each other by H­bonding. CCl4 molecules have no poles to attract the water molecules so the water molecules will remain together rather than surround the CCl4 molecules = no solution. Oct 7­9:34 AM
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Intermolecular Forces and Chemical Properties.notebook
March 26, 2015
1.
For each of the following pairs of molecules, draw the molecules with the correct VSEPR shape, classify the molecules as polar or nonpolar, and list the intermolecular forces that would exist between the molecules. Finally, predict which substance would have the higher melting point and explain why. a) SO2 and SiO2
b) AlCl3 and AsCl3 c) CH3F or F2
d) C4H10 or CH4
Oct 7­12:29 PM
2.
Diatomic molecules such as oxygen, nitrogen and chlorine tend to exist as gases at room temperature. Explain this observation based on intermolecular forces.
3.
Which hydrogen halide would you expect to have a higher boiling point: HCl or HBr? Explain your answer.
4.
What is the difference between a permanent molecular dipole in a polar molecule and an induced dipole in a non­polar molecule?
Oct 9­9:44 AM
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Intermolecular Forces and Chemical Properties.notebook
5.
March 26, 2015
What types of intermolecular forces must be broken to melt solid samples of the following? a) NH3
b) CH4
c) CH3OH
6.
In which compound, H2O or NH3, will the hydrogen bonding be stronger? Explain.
7.
List the following substances in order of increasing boiling points: CH3OH, SiO2, C2H6.
Oct 9­9:44 AM
8.
What are the molecular shapes of CCl4, CH3Cl, and CHCl3? In liquid samples of these compounds, which would have dipole­dipole forces between molecules? Oct 9­9:44 AM
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Intermolecular Forces and Chemical Properties.notebook
March 26, 2015
9.
At room temperature, CO2 is a gas, while silica, SiO2 is a hard solid. Compare the bonding in these two compounds to account for this difference in physical states.
10. Use the molecular modeling kits to create models of N2H4 and C2H4. Use your models to predict polarity and intermolecular forces in N2H4 and C2H4. Based upon the bonding between molecules, which of these two compounds would have a lower boiling point?
Oct 7­12:30 PM
Oct 9­9:45 AM
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Intermolecular Forces and Chemical Properties.notebook
March 26, 2015
Mar 25­12:22 PM
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