Question

Covalent molecules have low melting point because:
A. Covalent molecules are held by van der waals force of attraction
B. Covalent bond is less exothermic
C. Covalent bond is weaker than ionic bond
D. Covalent molecules have definite shape

Answer 1

To determine the answer we should know what the melting point is and what type of forces are present in covalent molecules. The melting point is the temperature required to convert the solid phase into the liquid phase. At melting point solid and liquid both phases exist in equilibrium. The melting point of the compound depends upon the strength of the forces present in the compound.

Complete step-by-step answer:
When atoms are held together by the sharing of electrons the formed bond is known as a covalent bond and the molecule is known as a covalent molecule. The covalent molecules are held together by van der Waals force of attraction to form compounds.

Similarly when atoms are held together by donation of electrons the formed bond is known as an ionic bond and the molecule is known as an ionic molecule. The ionic molecules are held together by the electrostatic force of attraction to form compounds.

The van der Waals force is weaker than the electrostatic force of attraction. So, covalent compounds require less energy to break the compound and for melting. So, covalent molecules have a low melting point because covalent molecules are held by van der Waals force of attraction which is a weak force.

Therefore, option (A) covalent molecules held by van der waals force of attraction, is correct.

Note: Atoms held together by the covalent bond are known as covalent molecules whereas if the atoms are held together by an ionic bond are known as ionic molecules. Molecules are held together by the force of attraction to form compounds. The covalent compounds have van der Waals force of attraction. The ionic compound has the electrostatic force of attraction. Electrostatic forces are stronger than van der Waals forces.