Short Answer
The properties of covalent compounds include low melting and boiling points because the forces between their molecules are weak. These compounds usually exist as gases, liquids, or soft solids. They do not conduct electricity because they do not contain free ions or electrons. Many covalent compounds are insoluble in water but dissolve in organic solvents like alcohol or kerosene.
These properties arise because covalent bonds involve sharing of electrons between non-metal atoms, forming molecules rather than ions. Examples include water, sugar, carbon dioxide, oxygen gas, and methane.
Detailed Explanation :
Properties of Covalent Compounds
Covalent compounds are substances formed when atoms share electrons to achieve a stable electron arrangement. They are usually formed by non-metal atoms with similar electronegativity. The bonding in covalent compounds gives rise to a unique set of properties that make them different from ionic and metallic substances. These properties depend on the strength of forces between molecules, the nature of electron sharing, and the molecular structure.
Understanding the properties of covalent compounds helps explain their behaviour in daily life, their uses in industry, and their role in chemical and biological systems. The following sections describe the major characteristics that define covalent compounds.
Low Melting and Boiling Points
One of the key properties of covalent compounds is their low melting and boiling points. Although covalent bonds inside molecules are strong, the forces between different molecules (called intermolecular forces) are generally weak. Because of this, only a small amount of heat energy is needed to separate these molecules.
This is why many covalent compounds exist as:
- Gases (oxygen, nitrogen)
- Liquids (water, ethanol)
- Soft solids (sulfur, wax)
These low melting and boiling points distinguish covalent compounds from ionic compounds, which have very high melting and boiling points.
Do Not Conduct Electricity
Covalent compounds do not conduct electricity, neither in solid nor in liquid form. This is because:
- They do not have ions.
- They do not contain free-moving electrons.
- Their molecules remain neutral.
Since electricity requires charged particles to move, covalent compounds cannot conduct electricity. Water itself is covalent but becomes a conductor only when ionic substances dissolve in it.
Poor Solubility in Water
Most covalent compounds are insoluble or only slightly soluble in water. Water is a polar solvent, and covalent molecules are often non-polar. This makes them difficult to dissolve in water.
However, covalent compounds dissolve well in organic solvents such as:
- Alcohol
- Ether
- Benzene
- Kerosene
This is because non-polar substances dissolve in non-polar solvents.
Exist as Molecules
Covalent compounds exist as molecules, not ions. A molecule is a group of atoms bonded together by shared electrons. These molecules may be small (like CO₂) or large and complex (like proteins and plastics).
This molecular nature explains many of their physical properties, such as softness, lower density, and flexibility.
Soft and Brittle (When Solid)
When covalent compounds form solids, they are usually soft and brittle. They do not have the strong ionic lattice found in ionic compounds. Their molecules are held loosely, making them easy to break apart.
For example:
- Wax can be scratched easily.
- Sulfur crystals break when pressed.
Some covalent solids like diamond and quartz are exceptions, but these involve network covalent bonding, which is extremely strong.
Do Not Form Ions
Covalent compounds do not form ions because electrons are shared, not transferred. As a result:
- No positive or negative ions exist.
- They do not conduct electricity.
- They do not react like ionic substances in water.
This property also affects their behaviour during chemical reactions.
Low Density and Volatility
Many covalent compounds have low density and high volatility (they evaporate easily). Perfumes, petrol, and many organic liquids evaporate quickly because the forces holding their molecules are weak.
Examples of Covalent Compounds
Common examples include:
- Water (H₂O)
- Oxygen (O₂)
- Carbon dioxide (CO₂)
- Methane (CH₄)
- Sugar (C₁₂H₂₂O₁₁)
These compounds show the typical covalent properties discussed above.
Important Applications
Because of their properties, covalent compounds are widely used:
- Fuels (methane, petrol)
- Medicines
- Plastics and polymers
- Fertilizers
- Food products
Their flexibility and wide range of structures make them essential in many industries and natural processes.
Conclusion
Covalent compounds have distinct properties such as low melting and boiling points, poor electrical conductivity, solubility in organic solvents, and molecular structures. These properties arise from the sharing of electrons between non-metal atoms and the weak forces between molecules. Understanding these characteristics helps explain their behaviour in everyday life, their uses in industries, and their importance in living organisms.