Video Transcript
Why do covalent compounds have
lower melting and boiling points compared with ionic compounds? (A) Covalent compounds have weak
intermolecular forces between the molecules. (B) Covalent compounds do not
conduct electricity. (C) Covalent compounds have strong
intermolecular forces between the molecules. (D) Covalent compounds have very
weak bonds between the atoms. (E) Covalent compounds do not form
between metals and nonmetals.
This question is asking about the
difference between covalent compounds and ionic compounds. In an ionic compound, a lattice of
positive and negative ions forms, held together by electrostatic attractions. Covalent compounds, on the other
hand, are generally made up of groups of molecules held together by intermolecular
forces. How do these structures relate to
the melting and boiling points of these compounds?
Well, the attraction between a
positive ion and a negative ion in an ionic compound is very strong. Since the particles are rigidly
held together, essentially all ionic compounds exist as solids at room
temperature. On the other hand, covalent
compounds are held together by weaker intermolecular forces, such as dipole–dipole
interactions or hydrogen bonds. Because the molecules are only
weakly held together, covalent compounds exist as liquids or gases at room
temperature. So we can see from the states of
these compounds that ionic compounds have higher melting points and boiling
points. And covalent compounds have lower
melting points and boiling points.
The primary reason for these lower
boiling and melting points is the weaker intermolecular forces that more loosely
hold together the structure. This reason corresponds with answer
choice (A), the correct answer. Covalent compounds have weak
intermolecular forces between the molecules.
So, why do covalent compounds have
lower melting and boiling points compared with ionic compounds? Choice (A), covalent compounds have
weak intermolecular forces between the molecules.
