Explain in terms of forces between structural units why H2O2 has a higher melting point than C3H8. Also, which of the following has a lower melting point?
NH3 or AsH3
C3H7OH or C2H5OCH3
I know that this has to do with hydrogen bonding. Can you possibly briefly explain hyrdrogen bonding or if you know one, give me a good website that simply explains hydrogen bonding/chemistry in general? (like dr. math only for chem)
To understand why H2O2 has a higher melting point than C3H8, we need to consider the forces between the structural units of these compounds. H2O2 is hydrogen peroxide, while C3H8 is propane. Both compounds are held together by intermolecular forces, which are forces of attraction between molecules.
In the case of H2O2, the molecule consists of two oxygen atoms and two hydrogen atoms. The oxygen atoms in H2O2 are highly electronegative, which means they tend to attract electrons towards themselves. As a result, the oxygen atoms in H2O2 develop a slightly negative charge, while the hydrogen atoms develop a slightly positive charge. This uneven charge distribution leads to the formation of hydrogen bonds between adjacent H2O2 molecules.
Hydrogen bonding is a special type of intermolecular force that occurs between a hydrogen atom bonded to a highly electronegative atom (such as oxygen, nitrogen, or fluorine) and another electronegative atom in a different molecule. These bonds are stronger than the standard dipole-dipole forces found in molecules like C3H8.
In contrast, C3H8 (propane) consists only of carbon and hydrogen atoms. The electronegativity difference between carbon and hydrogen is relatively small, resulting in weaker intermolecular forces between C3H8 molecules compared to the hydrogen bonds in H2O2.
Therefore, H2O2 has a higher melting point than C3H8 due to the presence of hydrogen bonding, which requires more energy to break the stronger intermolecular forces.
Now, moving on to the comparisons of melting points between different compounds:
NH3 (ammonia) and AsH3 (arsine) both exhibit hydrogen bonding due to the presence of hydrogen atoms bonded to electronegative atoms (nitrogen and arsenic, respectively). However, NH3 has a lower molecular weight and a smaller size compared to AsH3, which leads to stronger hydrogen bonding in NH3. Therefore, NH3 has a higher melting point than AsH3.
For the comparison between C3H7OH (propanol) and C2H5OCH3 (ethyl methyl ether), C3H7OH has the ability to form hydrogen bonds due to the presence of an -OH (hydroxyl) group. In contrast, C2H5OCH3 does not have a hydrogen atom bonded to an electronegative atom, so it cannot form hydrogen bonds. Therefore, C3H7OH has a higher melting point than C2H5OCH3.
To learn more about hydrogen bonding and general chemistry concepts, you can visit websites such as Khan Academy (www.khanacademy.org) or ChemGuide (www.chemguide.co.uk). These sites provide comprehensive explanations and resources on various chemistry topics, including hydrogen bonding.