2.6. Characteristics of Covalent Compounds

● Lower melting and boiling points compared to ionic compounds.

Covalent compounds generally have lower melting and boiling points than ionic compounds. This is because the forces holding the molecules together in covalent compounds are weaker than the strong ionic bonds found in ionic compounds. In ionic compounds, ions are held together by strong electrostatic forces, requiring more energy (in the form of heat) to break these bonds. In contrast, covalent compounds are held together by covalent bonds, and their intermolecular forces (like van der Waals forces) are weaker, leading to lower melting and boiling points.

Think of making tea. When you boil water (which has a high boiling point due to its ionic properties), it requires quite a bit of heat. Now, think of a soft drink that can fizz at room temperature - it wouldn't take much to change its physical state, just like covalent compounds. That's the difference between ionic and covalent substances!

● May be gases, liquids, or solids.

Covalent compounds can exist in various states—gases, liquids, or solids—depending on their molecular structure and the forces acting between their molecules. For example, water (H2O) is a liquid, carbon dioxide (CO2) is a gas, and sugar (C12H22O11) is a solid at room temperature. The state of a covalent compound is influenced by the strength of the intermolecular forces and the size of the molecules involved.

Imagine how some substances are different in states based on their properties. Like the water we drink is liquid (H2O), the air we breathe is a gas (CO2 in small amounts), and when we bake cookies, we use sugar, which is solid. All of these substances are made of covalent bonds but differ in their states!

● Usually insoluble or less soluble in water.

Many covalent compounds are either insoluble or have lower solubility in water compared to ionic compounds. This occurs because covalent compounds do not form ions in solution, which is typically necessary for solubility in polar solvents like water. For example, oils, which are covalent compounds, do not mix with water because the water molecules cannot effectively interact with the larger, non-polar molecules of oil.

Think about how oil and water do not mix. When you try to make a salad dressing with oil and vinegar, the two separate. Oil (a covalent compound) sits on top because it doesn't dissolve in water, showcasing how many covalent compounds behave in aqueous solutions!

● Do not conduct electricity (no free ions).

Covalent compounds typically do not conduct electricity when dissolved in water or in their solid state because they do not have free-moving ions. Unlike ionic compounds, where the ions can move freely and carry an electric charge, covalent compounds only share electrons and do not dissociate into ions. Therefore, when it comes to electricity, they are generally insulators, unlike ionic compounds, which can conduct electricity due to their ionization in solution.

Think of an insulated wire that cannot conduct electricity. Just like that wire, many covalent compounds do not let electric current flow through them. For example, if you try to pass electricity through sugar dissolved in water, it won't work. On the other hand, dissolving table salt (an ionic compound) in water allows for electric current to flow!

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