Join 60,000+ competitive exam aspirants
or with email
Your Cart
SubtotalтВ╣0
TotalтВ╣0
Examoogle тАв User тАв info@examoogle.com тАв EE-2024-8821
Chapter 1 of 12 тАв Page 1 of 248ЁЯФТ Protected PDF тАв Watermarked
Join 60,000+ competitive exam aspirants
Covalent molecules have low melting and boiling point because:
they are generally gaseous in nature
they have weak intermolecular forces
they have strong bonds within the molecule
they have strong electrostatic intermolecular forces
they have weak intermolecular forces
Covalent molecules consist of atoms held together by strong covalent bonds within the molecule; however, the forces holding individual molecules together are relatively weak intermolecular forces (such as London dispersion forces or dipole-dipole interactions). Because these intermolecular forces are easily broken, these substances require little energy to transition from solid to liquid or liquid to gas, resulting in low melting and boiling points.
Covalent molecules consist of atoms held together by strong covalent bonds within the molecule; however, the forces holding individual molecules together are relatively weak intermolecular forces (such as London dispersion forces or dipole-dipole interactions). Because these intermolecular forces are easily broken, these substances require little energy to transition from solid to liquid or liquid to gas, resulting in low melting and boiling points.
Think of a crowd at a concert: individual people (atoms) are holding hands tightly (covalent bonds), but the groups of people themselves are just loosely bumping into each other (intermolecular forces). If you want to scatter the crowd, you don't need to break their hands; you just need to break the weak 'social' proximity between the groups.
EtotalтАЛ=EintramolecularтАЛ+EintermolecularтАЛ тАФ total energy balance for phase change
FLondonтАЛтИЭr61тАЛ тАФ relative weakness of dispersion forces with distance
In covalent solids (molecular solids), the internal structure involves electron sharing between non-metal atoms. Unlike ionic lattices held by strong electrostatic forces, these molecular units are held in a crystal lattice by weak van der Waals forces. Thermal energy added to the system is spent overcoming these weak attractions rather than breaking the high-energy covalent bonds within the molecules themselves.
Intramolecular covalent bonds are very strong (sharing of electrons).
Intermolecular forces (van der Waals, hydrogen bonding) are much weaker than ionic bonds.
Molecular solids generally do not conduct electricity because they lack free ions or electrons.
Substances like CO2тАЛ, CH4тАЛ, and H2тАЛO are classic examples of covalently bonded molecular structures.
Volatile nature is useful in fuels (e.g., petrol/gasoline).
Low boiling points allow for easy phase changes for refrigeration cycles.
Not suitable for high-temperature structural applications compared to ionic or metallic compounds.
Used as organic solvents in chemical laboratories.
Basis of most fuels and organic polymers.
| Feature | Covalent Bond | Intermolecular Force |
|---|---|---|
Bond/Force Strength | Strong (Intramolecular) | Weak (Intermolecular) |
Exception: Giant covalent structures like Diamond or Silicon Dioxide (SiO2тАЛ) have very high melting points because they form a network of covalent bonds in 3D.
Option A: While many are gases, some are solids (e.g., sugar), so 'gaseous' is not the definition of why they have low melting points.
Option C: Strong bonds within the molecule are why the molecule remains intact, not why the substance melts easily.
Option D: Ionic molecules have strong electrostatic forces, which leads to HIGH melting points.
B is correct тАФ Covalent molecules have weak intermolecular forces that require minimal thermal energy to overcome.
If the question asks about high melting points, always look for 'Giant Covalent' (network solids) or 'Ionic' (lattice) keywords instead.
Get instant step-by-step AI explanations, full shift Previous Year Papers (SSC GD, RRB, SSC JE), and regional rank analysis on the official Examoogle App.
Free Download тАв 100K+ Aspirants