which of the following compounds would you expect to exhibit only London forces?
CCL4
CCLH
CaI2
PCl5
CCl4 and PCl5 because they are the only symmetrical molecules (and on-ionic) in the list.
To determine which of the compounds would exhibit only London forces, we must consider the types of intermolecular forces present in each compound.
There are three primary types of intermolecular forces: London dispersion forces, dipole-dipole forces, and hydrogen bonding.
London dispersion forces occur in all molecules and are caused by temporary fluctuations in electron distribution that create instantaneous dipoles. These forces are generally weak but can become significant in larger, more polarizable molecules.
Dipole-dipole forces occur between polar molecules and are caused by the attraction between the positive end of one molecule and the negative end of another. These forces are stronger than London forces and play a role in compounds with polar bonds.
Hydrogen bonding is a special type of dipole-dipole force that occurs when a hydrogen atom is bonded to a highly electronegative atom (such as oxygen, nitrogen, or fluorine) and interacts with another electronegative atom through a strong dipole-dipole attraction.
Now let's analyze each of the compounds:
1. CCl4 (carbon tetrachloride): London forces are present in CCl4 since it is a nonpolar molecule due to the symmetrical arrangement of chlorine atoms around the carbon atom.
2. CClH (chloroform): In CClH, London forces are present, but there are also dipole-dipole forces due to the polarity of the C-Cl bond.
3. CaI2 (calcium iodide): Calcium iodide is an ionic compound composed of Ca2+ and I- ions. Thus, it exhibits ionic bonding and does not have intermolecular forces but rather strong intramolecular forces.
4. PCl5 (phosphorus pentachloride): PCl5 is a nonpolar molecule due to its trigonal bipyramidal shape. Hence, it only exhibits London forces.
Therefore, among the given compounds, only CCl4 and PCl5 would be expected to exhibit only London forces.
London (dispersion) forces are the weakest intermolecular forces and occur between all molecules, regardless of their polarity. These forces result from temporary fluctuations in electron density that induce temporary dipoles in neighboring molecules.
To determine which compounds exhibit only London forces, we need to look at the molecular structure and the types of intermolecular forces present in each compound.
1. CCl4 (carbon tetrachloride):
CCl4 is a nonpolar molecule with a tetrahedral geometry. The four chlorine atoms surrounding the central carbon atom are symmetrically arranged, leading to a net dipole moment of zero. Hence, CCl4 only exhibits London forces.
2. CClH (chloroform):
CClH is also a nonpolar molecule since the dipole moments of the C-Cl bonds cancel each other out with the H atom. Therefore, CClH similarly only exhibits London forces.
3. CaI2 (calcium iodide):
CaI2 is an ionic compound composed of Ca2+ cations and I- anions. Ionic compounds do not have discrete molecules; instead, they form a crystal lattice held together by electrostatic attractions between the charged ions. Although London forces may exist between neighboring CaI2 units, the primary forces present in CaI2 are ionic forces, not London forces.
4. PCl5 (phosphorus pentachloride):
PCl5 is a polar molecule with a trigonal bipyramidal geometry. The chlorine atoms surrounding the central phosphorous atom are not uniformly distributed, thus creating a permanent dipole moment. In addition to London forces, PCl5 can also exhibit dipole-dipole interactions. Therefore, PCl5 exhibits both London forces and dipole-dipole interactions.
In summary, only CCl4 and CClH would be expected to exhibit only London forces.