For each of the four pairs of compounds, which would you expect to have the higher melting point based on the operative bonding mechanism?

NaCl and KBr
HF and CF4
CF4 and CHI3
H2 and Br2

Pls try and help me :( xX

NaCl

HF
CHI3
Br2
by amar chauhan

right!!!

Dear Anonymous,

I found the you again leaking the MITx mid term examination, and you leak not only one or two questions. You leaked so many of them. What do you wish from taking this course? The consideration to cancel out the first time FREE certificate may be passed to the faculty members.

Regards.

Jiskha is not part of the MITx platform!!! How the honor code of MITx could be applied to an user of other system?

Anon,

It's less about leaking the questions and more about having other people answer exam questions for you.

Sure! I'd be happy to help you.

To determine which compound in each pair is expected to have a higher melting point, we need to consider the bonding mechanism operating in each compound.

1. NaCl and KBr:
Both NaCl and KBr are ionic compounds formed by the transfer of electrons from one atom to another, resulting in the formation of positive and negative ions. In general, compounds with stronger ionic bonds tend to have higher melting points. The strength of ionic bonds depends on the charge of the ions and the distance between them. Since both NaCl and KBr have similar charges and similar ionic radii (size), we can expect them to have similar strengths of ionic bonding. Therefore, they would have similar melting points, but if we had to choose one, KBr might have a slightly higher melting point due to the larger size of the potassium ion compared to sodium ion.

2. HF and CF4:
HF is a polar covalent compound, where the hydrogen atom forms a partial positive charge, and the fluorine atom forms a partial negative charge. CF4, on the other hand, is a nonpolar covalent compound, where the carbon atom and four fluorine atoms share electrons equally. Generally, compounds with stronger intermolecular forces tend to have higher melting points. The polar nature of HF allows for stronger intermolecular dipole-dipole forces compared to the nonpolar CF4, which only has weaker dispersion forces. Therefore, HF is expected to have a higher melting point than CF4.

3. CF4 and CHI3:
Both CF4 and CHI3 are nonpolar covalent compounds. Similar to the previous explanation, compounds with stronger intermolecular forces tend to have higher melting points. Between these two compounds, CHI3 has a stronger intermolecular force due to the presence of iodine atoms, which are more massive and create stronger dispersion forces compared to the smaller fluorine atoms in CF4. Therefore, CHI3 is expected to have a higher melting point than CF4.

4. H2 and Br2:
Both H2 and Br2 are nonpolar covalent compounds. As nonpolar molecules, their intermolecular forces are composed of weak dispersion forces. When comparing compounds with similar atomic masses, larger molecules tend to have stronger dispersion forces. Therefore, Br2, which consists of larger molecules compared to H2, is expected to have a higher melting point than H2.

It's important to note that these explanations are based on general trends and approximations, as other factors like crystal structure and molecular shape can also influence melting points.