Question

Covalent bonded compounds have low melting and boiling point because of :

• A. Sharing of an electron pair between two atoms.
• B. Weak intermolecular forces.
• C. Attraction between molecules is very large.
• D. None of these

Hint:

Always distinguish between intramolecular forces (chemical bonds within a molecule) and intermolecular forces (forces between molecules).
Low boiling point is a feature of molecular substances with weak intermolecular forces.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks to identify the molecular reason why simple covalent compounds generally have low melting and boiling points compared to ionic compounds.

Step 2: Key Formula or Approach:
We must differentiate between strong intramolecular bonds (within molecules) and weak intermolecular forces (between separate molecules).

Step 3: Detailed Explanation:

• In covalent compounds, atoms within a molecule are held together by strong, localized covalent bonds (sharing of electron pairs).

• However, the separate individual molecules are held together in the bulk phase by much weaker attractive forces, collectively known as intermolecular forces (such as London dispersion forces, dipole-dipole interactions, or hydrogen bonding).

• When a covalent substance melts or boils, these strong covalent intramolecular bonds are not broken. Only the weak intermolecular forces between the molecules are overcome.

• Because these intermolecular forces require relatively little thermal energy to disrupt, most simple covalent molecular substances have relatively low melting and boiling points.


Step 4: Final Answer:
Covalent compounds have low melting and boiling points due to weak intermolecular forces.