Why is the ionic compound NaCl (table salt) able to dissolve in a glass of the molecular compound water (H2O)?
Partly because both are polar and like dissolves like.
Solvation, or the ability of a substance to dissolve in another substance, is determined by the nature of the particles involved. In the case of NaCl (sodium chloride) dissolving in water (H2O), the unique properties of both substances play a crucial role.
To understand why NaCl can dissolve in water, let's first discuss the nature of these compounds:
NaCl is an ionic compound: It consists of positively charged sodium ions (Na+) and negatively charged chloride ions (Cl-), held together by strong ionic bonds. These ions are attracted to each other due to their opposite charges.
Water, on the other hand, is a molecular compound composed of two hydrogen atoms (H) and one oxygen atom (O), forming a bent shape. Water molecules are polar, meaning they have a slightly positive charge on one end (hydrogen side) and a slightly negative charge on the other end (oxygen side). This polarity arises due to the electronegativity difference between oxygen and hydrogen.
Now, let's delve into how these properties enable NaCl to dissolve in water:
1. Ionic Bond Breaking: The positive and negative charges in the NaCl crystal lattice are relatively strong, but when NaCl is introduced to water, the polar water molecules exert forces on the crystal lattice. This weakens the ionic bonds, causing the Na+ and Cl- ions to separate from each other, becoming surrounded by water molecules.
2. Ion-Dipole Interactions: Once the ionic bonds are broken, the water molecules align themselves around the separated Na+ and Cl- ions through ion-dipole interactions. This occurs because the positive end of the water molecule is attracted to the chloride ion (negative), while the negative end is attracted to the sodium ion (positive). This process is commonly known as hydration.
3. Hydration Energy: The formation of hydrated ions is energetically favorable. It releases energy in the form of hydration energy, which compensates for the energy required to break the ionic bonds in the solid crystal lattice.
Overall, the polarity of water molecules and the ionic nature of NaCl enable the dissolution process to occur. The water molecules surround and disperse the Na+ and Cl- ions, resulting in a homogeneous mixture throughout the solution.
Understanding the properties of the substances involved allows us to explain why NaCl dissolves in water. By combining the knowledge of ionic compounds, polar molecules, and intermolecular forces, we can comprehend the underlying mechanism behind the phenomenon.