Fundamentals of Chemical Bonding and Compounds

Posted on Apr 28, 2025 in Chemistry

Chemical Bonds

Covalent Bond Types

A covalent bond takes place between atoms that share pairs of electrons. The type depends on the electronegativity difference (ΔEN) between the atoms:

  • Nonpolar covalent: Occurs between atoms sharing electron pairs with an electronegativity difference of zero (ΔEN = 0).
  • Polar covalent: Occurs between atoms sharing electron pairs with an electronegativity difference greater than 0 but less than 1.7 (0 < ΔEN < 1.7).
  • Coordinate covalent bond: In this bond, one atom provides both electrons for the shared pair, and the other atom provides an empty orbital.
  • Multiple covalent bonds:
    • Single: Occurs when only one pair of electrons is shared.
    • Double: Occurs when two atoms share two pairs of electrons.
    • Triple: Occurs when two atoms share three pairs of electrons.

Other Bond Types

  • Metallic bond: This bond is due to the movement of valence electrons in an energetic band formed by the overlap of sublevels.
  • Van der Waals forces: These are purely electrostatic forces; therefore, they occur as the attraction between opposite electrical charges.

Orbital Hybridization

Electron orbital hybridization is the formation of new orbitals by the orderly mixing of different atomic orbitals, resulting in the formation of hybrid orbitals.

  • sp³ hybridization: For example, a 2s² electron jumps to a 2p orbital if it lacks the last orbital, forming 2sp³ hybrid orbitals.

Atomic & Molecular Properties

Key Atomic Properties

  • Atomic radius: The distance from the nucleus of an atom to its outermost electron shell.
  • Ionic radius: The distance from the nucleus to the farthest electron in an ion.
    • When an atom gains electrons, it forms a negative ion called an anion. Anions tend to have a radius greater than the original atom.
    • When an atom loses electrons, it forms a positive ion called a cation. Cations have an ionic radius smaller than the original atom.
  • Electron affinity: The energy released when a neutral atom gains an electron to produce a negative ion.
  • Electronegativity: The attraction of atoms for electrons that form a chemical bond.
  • Oxidation state (or oxidation number): An integer that indicates the ability of an element to combine chemically.

Bonding Principles & Rules

  • Chemical bond: The force that holds two atoms or two oppositely charged ions together.
  • Types of chemical bonds:
    • Interatomic: Ionic, Covalent (Polar, Nonpolar, Single, Double, Triple, Coordinated), Metallic
    • Intermolecular: Hydrogen bond, Van der Waals forces
  • Valence: The combination capacity of an atom.
  • Oxidation number: A positive or negative integer that describes the combining ability of an atom.
  • Octet rule: Atoms gain or lose electrons to acquire a stable group of 8 electrons in their valence shell.
  • Calculating valence in ternary compounds: The first element is typically positive, the last is negative, and the element in the middle has a value that makes the compound neutral.
  • Structural rules:
    • Group 1 elements typically form only 1 bond and often go on the ends of a structure.
    • Oxygen should always form 2 bonds (in most common compounds).
    • Two atoms of the same element cannot be directly bonded unless they are carbon atoms (in organic compounds).
    • Nonmetals tend to complete 8 electrons in their structure, but some nonmetals can accommodate up to 10 or 12 electrons (expanded octet).

Chemical Compound Naming

Compound Classes

  • Oxides: Metal (M) + O, Nonmetal (NM) + O
  • Hydroxides: M + O + H
  • Hydrides: Metallic (M + H), Nonmetallic (NM + H)
  • Acids: Hydracids (M + NM), Oxyacids (H + NM + O)
  • Salts: Binary (M + NM), Oxysalts (M + NM + O)

Naming Systems

Common naming conventions include:

  • Systematic (IUPAC): Uses prefixes to indicate the number of atoms (e.g., PCl₅ – phosphorus pentachloride). Valences are used to determine formulas, and prefixes indicate stoichiometry.
  • Stock: Uses Roman numerals in parentheses to indicate the oxidation state of the metal (e.g., Iron(II) oxide).
  • Trivial/Common: Traditional names (e.g., water, ammonia). Anhydrides (acid oxides) might use prefixes like trioxide or pentaoxide.

Note: The original text’s description of naming was fragmented and mixed different systems. This section provides a simplified overview based on common practices.

Properties of Compounds

Ionic Compound Properties

  • Solid at room temperature.
  • High melting point.
  • Water soluble.
  • Insoluble in benzene.
  • Fused or dissolved in water, they are good conductors of electricity.

Covalent Compound Properties

  • Can be solids, liquids, or gases at room temperature.
  • If solid, have low melting points.
  • Low solubility in water and benzene (generally).
  • Some react with water to form ions and thus become electric current conductors.