Rank the following in order by increasing boiling point and explain why?
CH3Cl Rn CH4 CH3-CH2-OH
The lightest molecule is CH4, it should have the lowest boiling point.
Rn is next since it has no H bonding and no dipole.
CH3Cl should be next. It has a molar mass less than Rn but it has a dipole moment.
CH3CH2OH should be the highest since it has hydrogen bonding.
To rank the given compounds in order of increasing boiling point, we need to consider the intermolecular forces or attractions between the molecules. The strength of these forces determines how tightly the molecules are held together, thus affecting their boiling points.
1. Rn (Radon):
Radon is a noble gas and exists as single atoms. Noble gases have very weak intermolecular forces known as London dispersion forces. These forces result from temporary shifts in electron distribution, creating temporary partial charges. Among the given compounds, Rn has the weakest intermolecular forces because it is made up of single atoms, resulting in the lowest boiling point.
2. CH3Cl (Methyl Chloride):
CH3Cl is a polar molecule with a dipole moment. It exhibits dipole-dipole interactions between molecules. These forces are stronger than London dispersion forces because the positive end of one molecule attracts the negative end of another molecule. Therefore, CH3Cl has stronger intermolecular forces compared to Rn, resulting in a higher boiling point.
3. CH4 (Methane):
CH4 is a nonpolar molecule, and it only experiences London dispersion forces. Although London dispersion forces are generally weaker than dipole-dipole interactions, CH4 has fewer electrons, which means it has less surface area available for temporary shifts in electron distribution. As a result, CH4 has weaker intermolecular forces compared to CH3Cl, leading to a lower boiling point.
4. CH3-CH2-OH (Ethanol):
CH3-CH2-OH, also known as ethanol, is a polar molecule due to the presence of an -OH group. It experiences both dipole-dipole interactions and hydrogen bonding. Hydrogen bonding is a strong intermolecular force that occurs when a hydrogen atom is bonded to a highly electronegative atom, such as oxygen or nitrogen. Ethanol can form hydrogen bonds between the oxygen atom of one ethanol molecule and the hydrogen atom of another ethanol molecule. The presence of hydrogen bonding makes the intermolecular forces in ethanol stronger than CH3Cl and CH4, resulting in a higher boiling point.
Therefore, the compounds ranked in order of increasing boiling point are: Rn < CH4 < CH3Cl < CH3-CH2-OH.