I just posted a question about how to determine which compound (from a list of c
ID: 536997 • Letter: I
Question
I just posted a question about how to determine which compound (from a list of covalent compounds that all contain C as the central atom, with 4 other atoms around the C) has the lowest melting point, and how do you tell. The compounds are CF4, CH4, CI4, CBr4, and CCl4. The answer I got was that CH4 would have the lowest melting point, due to the fact that H has the lowest molecular mass, as compared with F, I, Br, and Cl. However, I actually looked up the melting points, and found that CF4 has the lowest melting point, not CH4. Melting point of CF4 is -298.5•F. Melting point of CH4 is -295.6•F. Now I'm confused... I just posted a question about how to determine which compound (from a list of covalent compounds that all contain C as the central atom, with 4 other atoms around the C) has the lowest melting point, and how do you tell. The compounds are CF4, CH4, CI4, CBr4, and CCl4. The answer I got was that CH4 would have the lowest melting point, due to the fact that H has the lowest molecular mass, as compared with F, I, Br, and Cl. However, I actually looked up the melting points, and found that CF4 has the lowest melting point, not CH4. Melting point of CF4 is -298.5•F. Melting point of CH4 is -295.6•F. Now I'm confused...Explanation / Answer
The forces we have just discussed are responsible for many of the bulk properties of a material. How strongly molecules are held together may be inferred from their melting points and boiling points. Molecular substances tend to have low melting and boiling points. Note that both rise as the molecules get larger. This is predicted by the description of London dispersion forces. Also, larger molecules with polar bonds may have higher than expected mp/bpOther things being equal, more symmetrical molecules will have higher melting points because they pack more efficiently meaning they have higher lattice energies. For this reason, the effect on boiling points is typically much smaller. This is the reason that CF4 has lowe melting point as compare to CH4