1. Polarity:
* "Like dissolves like": This is the fundamental principle. Water is a highly polar molecule, meaning it has a positive and a negative end due to uneven electron distribution. Substances that are also polar (like salts, sugars, and many alcohols) will dissolve well in water because their molecules can interact with water molecules through electrostatic attractions (hydrogen bonds and dipole-dipole interactions).
* Non-polar compounds: Compounds with little or no polarity (like oils and fats) will not dissolve in water. Their molecules cannot form strong attractive forces with water molecules.
2. Intermolecular forces:
* Hydrogen bonding: Strongest intermolecular force, forming between hydrogen atoms bonded to highly electronegative atoms (like oxygen or nitrogen). Compounds capable of hydrogen bonding with water are more likely to dissolve.
* Dipole-dipole interactions: Occur between polar molecules, weaker than hydrogen bonds but still contribute to solubility.
* London dispersion forces: Weakest forces, present in all molecules, but stronger in larger molecules. Non-polar compounds rely solely on these forces, which are insufficient for dissolving in water.
3. Molecular size and shape:
* Smaller molecules: Generally dissolve better because they can more easily interact with water molecules.
* Shape: If a molecule has a shape that allows for favorable interactions with water, it is more likely to dissolve.
4. Temperature:
* Increased temperature: Generally increases the solubility of solids and gases in water. This is because higher temperature provides more energy for molecules to overcome intermolecular forces and break apart.
5. Pressure:
* Increased pressure: Generally increases the solubility of gases in water. This is because higher pressure forces more gas molecules into solution.
In summary:
A compound is more likely to dissolve in water if it is polar, can form hydrogen bonds, is small and has a favorable shape, and the temperature is relatively high.
Exceptions and other factors:
* Ionic compounds: These dissolve in water by separating into their ions, which are then surrounded by water molecules.
* Some non-polar substances: Can have limited solubility in water due to weak interactions or interactions with specific parts of the molecule.
* Presence of other solutes: Can affect the solubility of a given compound.
It's important to remember that solubility is a complex phenomenon. While these are the main factors influencing it, there are many specific cases and exceptions.
