Names_______________________________________________________________
Chemistry Group Work: Intermolecular Forces
For questions 1-5:
a) Draw the 3-D Lewis structures, showing any polar bonds with + and - symbols in the
appropriate location.
b) Identify all of the intermolecular forces in each compound: (dispersion force, dipole
interaction or hydrogen bonding)
1)
carbon disulfide
2)
ammonia
3)
oxygen
4)
CH2F2
5)
C2H6
Verify your answers before going to the exercises on the back of this page.
Practice on Intermolecular Forces
1
Intermolecular_Forces_Group_Worksheet.odt
Rank the following compounds by increasing melting point. Explain your rankings completely,
including the most important intermolecular force in each molecule.
6)
C2H6, C2H5OH, C2H5F
7)
H2S, H2O, H2
8)
BBr3, BI3, BCl3
9) C (diamond) , H2O , NaCl, I2
Practice on Intermolecular Forces
2
Intermolecular_Forces_Group_Worksheet.odt
Intermolecular Forces - Key
For questions 1-5, identify the main type of intermolecular force in each compound:
1)
carbon disulfide
Dispersion Forces
2)
ammonia
Hydrogen bonding, dipole interaction and dispersion forces
3)
oxygen
Dispersion Forces
4)
CH2F2
Dipole Interaction and dispersion forces
5)
C2H6
Dispersion Forces
Rank the following compounds by increasing melting point:
6)
C2H6, C2H5OH, C2H5F
C2H6 (-183.30 C), C2H5F (-143.20 C), C2H5OH (-117.30 C)
C2H6 is non polar and only has dispersion forces. C 2H5F is a polar molecule and is held
together by dipole interactions, which are generally stronger than dispersion forces.
C2H5OH has hydrogen bonding which is stronger than either ordinary dipole interaction
and dispersion force.
7)
H2S, H2O, H2
H2 (-259.30 C), H2S (-85.50 C), H2O (00 C)
H2S and H2 are both non polar, but H2 has fewer electrons, resulting in weaker
dispersion force. H2O has a much higher melting point due to its much stronger
hydrogen bonding.
8)
BBr3, BI3, BCl3
BCl3 (-107.30 C), BBr3 (-460 C), BI3 (49.90 C)
All three molecules have dispersion force as their IM force, but BCl 3 has the fewest
electrons, giving it the lowest melting point.
9)
C (diamond) , H2O , NaCl, I2
H2O (00C) , I2 (113.7 °C) , NaCl (8010 C), Diamond (35500C)
Water has hydrogen bonding and iodine has dispersion forces. Iodine's melting point is
due to the fact that it has many more electrons than a water molecule, which gives it
rather strong dispersion forces. NaCl has ionic bonding which is much stronger than
any Van Der Waals force and diamond, a network solid is held together by covalent
bonding which is stronger than any of the other intermolecular forces.
Practice on Intermolecular Forces
3
Intermolecular_Forces_Group_Worksheet.odt
Practice on Intermolecular Forces
4
Intermolecular_Forces_Group_Worksheet.odt
Practice on Intermolecular Forces
5
Intermolecular_Forces_Group_Worksheet.odt