Consider the molecules ether (CH3OCH3), ethyl alcohol (CH3CH2OH), and propanol (CH3CH2CH2OH) (not isopropanol!).
The boiling point of ether is -25 degrees while the boiling point of ethyl alcohol is 78 degrees. How would you explain the difference in properties of the two molecules that explains why the difference in boiling points is so large?
Answer: Ethyl alcohol undergoes, hidrogen bonding while eter does not
Now compare the boiling point of ethyl alcohol (78 degrees) with that of propanol (98 degrees). How would you explain the difference in properties of the two molecules that explains the difference in boiling points?
Answer: Propanol is larger than ethyl alcohol, and therefore more polarizable.
Which molecule ( LiI or KI ) has the lower boiling point?
Answer: LiI because this is more ionic character than KI.
Propanol is higher largely because it is a larger molecule (molar mass is higher) and higher dispersion forces.
Are you sure the ionic character is higher in LiI? Li has electronegativity (EN) of about 0.98, K is about 0.82.
To answer the question about the boiling points of ether and ethyl alcohol, we need to consider their molecular structures and intermolecular forces. Boiling point is primarily influenced by the strength of these intermolecular forces.
Ether (CH3OCH3) is a small molecule and has a symmetrical structure. It is primarily held together by weak dispersion forces (London forces), which arise due to temporary imbalances in electron distribution. These forces are relatively weak, resulting in a low boiling point of -25 degrees Celsius.
On the other hand, ethyl alcohol (CH3CH2OH) also has dispersion forces, but it has an additional intermolecular force called hydrogen bonding. Hydrogen bonding occurs when a hydrogen atom is attached to a strongly electronegative atom, such as oxygen, nitrogen, or fluorine, and interacts with another electronegative atom. In the case of ethyl alcohol, the oxygen atom in one alcohol molecule can form a hydrogen bond with the hydrogen atom in another alcohol molecule. These hydrogen bonds are stronger than dispersion forces, leading to a higher boiling point of 78 degrees Celsius.
Now, let's compare the boiling point of ethyl alcohol with propanol (CH3CH2CH2OH). Propanol is a larger molecule than ethyl alcohol, and size affects the strength of dispersion forces. The larger the molecule, the greater the surface area available for temporary imbalances in electron distribution, leading to stronger dispersion forces. Thus, propanol has stronger dispersion forces than ethyl alcohol, resulting in a higher boiling point of 98 degrees Celsius.
Finally, considering the boiling points of LiI and KI, we need to analyze the nature of their bonding. Ionic compounds, like LiI and KI, have higher boiling points compared to molecular compounds because they possess strong electrostatic attractions between ions. However, the boiling point of an ionic compound is influenced by the magnitude of the charges and the size of the ions.
LiI has smaller ions and a higher charge compared to KI. The smaller size of the Li+ ion results in stronger attractive forces between ions, leading to a higher boiling point compared to KI. Therefore, LiI has a lower boiling point than KI.
In summary, the differences in boiling points for these molecules can be explained by the nature of intermolecular forces, the molecular size, and the ionic character of the compounds involved.