Chemistry Bonding Assignment

1994 Words Mar 10th, 2013 8 Pages
Chemistry 30
Chemical Bonding – Properties of Molecules

1. For the following molecules determine which atoms are bonded (write the symbols with a bond between them), the electronegativity difference between them, and the type of chemical bond it represents. If the bond is ionic, state what ions are produced. If the bond is polar covalent, indicate the direction of the dipole on the symbols from the first part.

a) KCl Electronegativity difference = K - Cl = 0.8 - 3.0 = 2.2 ionic bond K1+ Cl1- b) LiBr Electronegativity difference = Li - Br = 1.0 - 2.8 = 1.8 ionic bond Li1+ Br1- [pic] c) HI Electronegativity difference = H - I = 2.1 - 2.5 = 0.4 polar covalent bond
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Both have London dispersion force drawing them together.

These two are isoelectronic so the London force should be the same. This is manifested in similar boiling temperatures.

5. Why does liquid propane (C3H8) boil at a much lower temperature than gasoline (C8H18)?

Both are pure hydrocarbons and are non-polar (symmetry causes dipoles to cancel). Both have london dispersion force. Propane has 26 electrons, gasoline has 66. Since gasoline has more electrons, it has a higher london dispersion force and so has a higher boiling temperature than propane.

6. Given the following molecules:

i) methane iii) butane ii) propane iv) methyl propane

a) Draw each structure

[pic] [pic] [pic] [pic]

b) Predict the order of increasing melting point. Give reasons for your answer.

methane, propane, butane, methyl propane.

fewest electrons, lowest melting point. methyl propane is more compact than butane so it packs better in the solid phase and has the highest melting point.

c) Predict the order of increasing boiling point. Give reasons for your answer.

methane, propane, methyl propane, butane

fewest electrons, lowest boiling point. butane has more surface area in the liquid phase so more interactions with surrounding molecules give it a higher boiling point.

7. Both krypton (b.p. -152°C) and
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