Chemistry Bonding Assignment

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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) KClElectronegativity difference = K - Cl = 0.8 - 3.0 = 2.2ionic bond K1+ Cl1- b) LiBrElectronegativity difference = Li - Br = 1.0 - 2.8 = 1.8ionic bond Li1+ Br1- [pic]

c) HIElectronegativity difference = H - I = 2.1 - 2.5 = 0.4 polar covalent bond [pic]
d) CF4Electronegativity difference = C - F = 2.5 - 4.0 = 1.5polar covalent bond [pic]
e) CaSElectronegativity difference = Ca - S = 1.0 - 2.5 = 1.5polar covalent bond [pic]
f) H2SeElectronegativity difference = H - Se = 2.1 - 2.4 = 0.3polar covalent bond [pic]
g) SiCl4Electronegativity difference = Si - Cl = 1.8 - 3.0 = 1.2polar covalent bond h) P4Electronegativity difference = P - P = 2.1 - 2.1 = 0.0covalent bond [pic]

i) FeCl3Electronegativity difference = Fe - Cl = 1.8 - 3.0 = 1.2polar covalent bond j) BrCl7Electronegativity difference = Br - Cl = 2.8 - 3.0 = 0.2covalent bond k) CS2Electronegativity difference = C - S = 2.5 - 2.5 = 0.0covalent bond l) K2SElectronegativity difference = K - S = 0.8 - 2.5 = 1.7ionic bond K1+ S2-

2.For c, d, f, g, and k from question 1 determine whether the molecules are polar, or nonpolar. Show all work.
[pic]
c) HIElectronegativity difference = H - I = 2.1 - 2.5 = 0.4 polar covalent bond

shape: only 2 atoms[pic]

since only 2 atoms the dipole does not cancel; this is a polar molecule.

[pic]
d) CF4Electronegativity difference = C - F = 2.5 - 4.0 = 1.5polar covalent bond

shape: tetrahedral
[pic]

bond dipoles exist but because the molecule is symmetrical the forces cancel. This is a non-polar molecule.

[pic]
f) H2SeElectronegativity difference = H - Se = 2.1 - 2.4 = 0.3polar covalent bond

shape: angular
[pic]

bond dipoles exist and the shape causes the forces to reinforce each other. This is a polar molecule.

[pic]
g) SiCl4Electronegativity difference = Si - Cl = 1.8 - 3.0 = 1.2polar covalent bond

shape: tetrahedral
[pic]
bond dipoles exist but because the molecule is symmetrical the forces cancel. This is a non-polar molecule.

k) CS2Electronegativity difference = C - S = 2.5 - 2.5 = 0.0covalent bond

shape: linear (bonded to 2 atoms with no lone pairs)

[pic]

There are no bond dipoles; this is non-polar molecule.

3.Consider the following data:

ElementNumber of ElectronsBoiling Point (K)

Helium 2 4
Neon10 27
Argon18 87
Krypton36121
Xenon54166
Radon86211

Plot a graph of number of electrons (x-axis) vs boiling point (y-axis). Explain the trend.

[pic]

These are single, uncharged atoms and so are non-polar.

As a result the force drawing them together is London dispersion.

London dispersion force increases with increasing number of electrons; thus in the graph as the number of electrons increases, so does the London dispersion force, resulting in an increasing boiling...
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