Why Are Covalent Compounds Soluble in Organic Solvents but Not in Water?

Covalent compounds often exhibit different solubility characteristics in organic solvents compared to water. This phenomenon can be attributed to differences in polarity and the intermolecular interactions involved. In this article, we will explore these key reasons and the principle of like dissolves like, which guides our understanding of why covalent compounds are soluble in organic solvents.

Polarity and Solubility

Taking a closer look at the polargraphy of covalent compounds and water, we can better understand why these compounds show varying solubilities. Many covalent compounds are nonpolar or have low polarity. Nonpolar substances tend to dissolve well in nonpolar solvents such as organic solvents, which are characterized by similar intermolecular forces. In contrast, water is a polar solvent with strong hydrogen bonding and dipole-dipole interactions. Due to their low polarity, nonpolar covalent compounds do not interact favorably with water molecules, leading to low solubility.

The Principle of Like Dissolves Like

The principle like dissolves like is a fundamental rule in chemistry. It states that polar solvents dissolve polar solutes, and nonpolar solvents dissolve nonpolar solutes. Organic solvents, such as hexane, ether, and benzene, are often nonpolar or weakly polar, making them suitable for dissolving nonpolar covalent compounds. For example, ethyl alcohol (ethanol) can dissolve nonpolar molecules due to its partially polar hydroxy group and nonpolar hydrocarbon tail.

Intermolecular Forces and Solvability

The intemolecular forces in organic solvents, such as van der Waals forces, allow them to interact and mix with nonpolar covalent compounds. In contrast, the strong hydrogen bonds in water do not facilitate the solvation of nonpolar covalent compounds. This highlights why covalent compounds are generally more compatible with organic solvents, which share similar intermolecular forces with the covalent compounds.

Summary and Insights

Covalent compounds are generally soluble in organic solvents due to their nonpolarity and the presence of similar intermolecular forces in these solvents. This solubility in organic solvents is in direct contrast to their low solubility in water, which is a result of water's polarity and the lack of favorable interactions with nonpolar substances.

To illustrate, let's consider the solubility of a covalent compound such as an alkene (RCHCH2) in different solvents:

Ethyl alcohol (ethanol): This solvent is a good example of a solvent that can dissolve alkene due to its polar hydroxy group and nonpolar hydrocarbon tail. When compared to methanol, which has a shorter hydrocarbon chain, methanol is insoluble in hexanes, whereas ethanol is soluble. Ethanol's characteristics: Ethanol is not highly flammable, making it a safer choice for heating solutions. It also has a pleasant smell and is gentle on the skin, making it a preferred solvent for laboratory work. Laboratory-grade ethanol, however, is often denatured with small amounts of methanol or pyridine to render it unfit for consumption and thus exempt from alcohol taxes.

Understanding the solubility of covalent compounds is crucial for chemical processes and extraction methods. By recognizing the interplay between polarity and intermolecular forces, we can better predict and control the behavior of these compounds in different solvents.