Chemical Bonds and Intermolecular Forces Analysis

Dipole-Dipole and Dispersion Forces

Dipole-dipole forces are intermolecular forces established between the positive dipole of one molecule and the negative dipole of another. The polarity of a diatomic molecule is greater the larger the electronegativity difference.

London Dispersion Forces are intermolecular forces established between molecules due to the formation of instantaneous dipoles as a consequence of the movement of electrons. The intensity of these forces depends on the polarizability of the molecule and its size; these factors depend, in turn, on the number of electrons in a molecule.

Properties of Molecular Substances

Molecular substances can occur at any state of aggregation at room temperature. Their properties include:

• Melting and Boiling Points: Molecular solids have low melting points. The melting and boiling temperatures depend on the intensity of the intermolecular forces.
• Physical Characteristics: Molecular solids are typically soft and fragile.
• Conductivity: They do not conduct an electric current because their molecules are neutral.
• Solubility: Nonpolar molecular substances dissolve in nonpolar solvents, while polar molecular substances are soluble in polar solvents, such as water.

Properties of Covalent Network Solids

• Durability: These solids exhibit high melting temperatures and high hardness.
• Solubility: They are insoluble due to the strength of their links and their large molecular structure.
• Brittleness: They are fragile due to the directional character of the bond.
• Conductivity: They exhibit low conductivity because of the low mobility of electrons.

Ionic Solids

• Thermal Properties: They have high melting and boiling temperatures due to the high intensity of the electrostatic force between oppositely charged ions.
• Hardness and Solubility: They possess high hardness and are soluble in polar solvents due to the attraction of the ions (ion-dipole forces).
• Brittleness: These solids are fragile as a result of the displacement of one layer of ions over another.
• Conductivity: They do not conduct electricity in the solid state because ions occupy fixed positions in the network. However, they conduct in the liquid state or in solution because the ions are free to move.

Metallic Bonding

Metallic bonding is the electrostatic attraction between the positive ions of metallic elements and the electron cloud that surrounds them.

Properties of Metals

• Density and Luster: Metals exhibit high density and metallic luster (except for alkali metals) due to the efficient packing of atoms in the structure, as well as high mass and volume.
• Strength: They have high melting temperatures and hardness (except alkali metals) due to the forces of attraction between positive ions and electrons.
• Conductivity: They provide good electrical and thermal conductivity because of the high mobility of electrons.

Classification of Chemical Bonds

• Ionic Bond: Formed between a metal and a nonmetal.
• Covalent Bond: Formed between a nonmetal and a nonmetal.