INTERMOLECULAR?

Intermolecular Forces?

• 1. The temperature at which a substance melts or boils depends upon the strengths of the intermolecular forces. What must happen for a substance to melt in terms of particles, intermolecular forces, and energy? 2. What must happen in terms of particles, intermolecular forces, and energy for a given substance to boil? 3. Match Iron(II) oxide, Potassium Chloride, Aluminum Nitride with the following melting points: 770 C, 1369 C, 2200C.

• Answer:

  1. For a substance to melt, energy must be added (endothermic) to overcome the London forces, dipole-dipole forces, hydrogen bonding forces, and/or electrostatic (ionic) forces to allow the individual particles to move past one another. 2. For a substance to boil, the energy must be added as described in 1. plus the energy to separate the particles from each other by a longer distance. 3. K+ and Cl- 770 C (The charge product of the ions is 1 x 1 = 1) Fe2+ and O2- 1369 C (The charge product of the ions is 2 x 2 = 4) Al3+ and N3- 2200 C (The charge product of the ions is 3 x 3 = 9) The higher the charge product for ionic substances, the stronger the intermolecular forces and the higher the melting point. Note that iron (II) oxide is FeO, not Fe2O3.