Chemical Bonds and Solutions: Understanding Intermolecular Forces
Chemical Bonds
The set of forces that hold atoms together when they form molecules and crystals, as well as the forces that hold molecules together when they are in a solid or liquid state.
Ionic Bond
An ionic bond occurs between elements that have a large difference in electronegativity, generally between a metal and a non-metal. This bond involves a total transfer of electrons from the less electronegative atom to the more electronegative atom, resulting in both atoms achieving a noble gas configuration.
Properties:
- They are crystalline solids with high melting temperatures.
- They do not conduct electricity in the solid state, but they do when dissolved or molten.
- They are hard due to the great strength of their bonds.
- They are generally soluble in polar solvents, especially water. Water molecules dissolve around the separated ions, preventing them from recombining.
Covalent Bond
A covalent bond is formed between non-metal elements that share a pair of electrons and have similar electronegativity. It consists of a bond between two atoms. If one atom provides both electrons for the bond, the bond is called a covalent dative bond. This bond also achieves a noble gas configuration.
Properties:
- Most covalent substances are molecular.
- In the solid state, they do not have a specific aggregation; there are gaseous, liquid, and solid substances.
- Their melting and boiling points are low.
- They are not good conductors of electricity.
- They are insoluble in polar solvents.
- Organic covalent liquids are soluble in benzene.
- Their hardness is not high.
Intermolecular Forces
Intermolecular forces hold molecules of covalent substances together, allowing them to appear in solid or liquid states, or dissolved in other substances. In general, these bonds are much weaker than the bonds between atoms.
Hydrogen Bond
A hydrogen bond is an interaction that takes place between atoms in molecules where hydrogen (H) is attached to other highly electronegative, small atoms, such as in HF, H2O, and NH3 bonds. The interaction occurs between hydrogen atoms of molecules that are linked to other highly electronegative, small atoms.
Solutions
Components of a Solution
A solution is a homogeneous, uniform, and stable mixture consisting of two or more substances called components. It consists of:
- Solute: The component that changes phase when the dissolution occurs; also called the dispersed body.
- Solvent: The component that dissolves the solute. The substance present in greater quantity is often called the solvent.
The solute can be a gas, liquid, or solid, and the solvent can also be a gas, liquid, or solid.
Solubility
Solubility is the maximum amount of solute (grams of substance) that can be dissolved in 100 grams of solvent at a fixed temperature to form a saturated solution.
Factors Affecting Solubility
- Temperature: Solubility varies with temperature.
- Common Ion Effect: The shift in ionic equilibrium when the concentration of one of its ions changes, due to the presence of a salt that contains it.
- Dissolution of Precipitates: Several methods exist, including:
- Formation of weak electrolytes.
- Oxidation-reduction reactions.
- Formation of a complex ion.
Ways to Express Solubility
Percentage by Mass: The mass percentage of solute contained in the solvent; that is, the mass of solute expressed in grams.