Chemical Bonding: Ionic, Covalent, and Metallic Properties
Ionic Bonds
An ionic bond unites ions with opposite charges through electrostatic attraction. Lattice energy, released during ionic bond formation from gaseous ions, determines the bond’s stability. Higher lattice energy indicates stronger attraction and a more stable ionic network.
Properties of Ionic Compounds
- Solids at room temperature, forming crystal lattices.
- High melting and boiling points due to strong electrostatic forces.
- Hard and brittle due to low compressibility.
- Soluble in polar solvents like water.
- Zero electrical conductivity in solid state, but conductive when molten or in solution.
Covalent Bonds
A covalent bond involves sharing electron pairs between atoms. Bond length is the equilibrium distance between atoms, measured in Angstroms. Shorter bond length indicates a stronger bond. Bond angle, measured in degrees, is formed by imaginary lines through the centers of bonded atoms.
Lewis Theory
Gilbert Newton Lewis proposed that covalent bonds involve sharing electron pairs to achieve a noble gas electron configuration.
VSEPR Theory
Valence Shell Electron Pair Repulsion (VSEPR) theory predicts molecular geometry based on minimizing electron pair repulsion.
Polarity
Charge separation in a molecule creates a dipole moment, measured in Debye (D), pointing towards the more electronegative element.
Properties of Covalent Substances
Atomic Substances
- Crystalline solids with high melting points (e.g., graphite, diamond, quartz).
- Graphite conducts electricity due to electron mobility.
- Generally insoluble in water.
Molecular Substances
- Solids, liquids, or gases at room temperature, depending on molecular mass.
- Lower melting and boiling points compared to atomic substances.
- Generally non-conductive, except for highly polar compounds in aqueous solutions.
- Nonpolar molecules dissolve in nonpolar solvents, while polar molecules dissolve in polar solvents.
Metallic Bonds
Metals form lattices with cations arranged in space and freely moving electrons.
Properties of Metals
- High thermal and electrical conductivity due to electron mobility.
- Deformable, ductile, and malleable.
- High melting and boiling points.
- High density.
- Photoelectric effect: emission of electrons upon light impact.