Concepts of Chemical Bonding

Chemical Bonds

  • Three types:

  • Ionic: Electrostatic attraction between ions

  • Covalent: Sharing of electrons

  • Metallic: Free electrons hold metal atoms together

Lewis Symbols

  • Developed by G. N. Lewis to denote bonding electrons using dots for valence electrons

  • Atoms tend to gain, lose, or share electrons to achieve eight valence electrons (octet rule)

Ionic Bonding

  • Involves metals and nonmetals

  • Characterized by electron transfer

  • Properties include brittleness, high melting points, and crystalline structure

Energetics of Ionic Bonding

  • Born-Haber cycle diagrams the formation of ionic compounds

  • Ion formation is endothermic (cation) and exothermic (anion); overall exothermic process

  • Lattice Energy: Energy to separate moles of ionic compound into gaseous ions

Born Haber cycle of magnesium chloride

Covalent Bonding

  • Atoms share electrons with various interactions: attractions and repulsions between electrons and nuclei

  • Total attractive interactions must exceed repulsive interactions for bond formation

Stone Structures & Formal Charges

  • Lewis structures help visualize sharing of electrons

  • Formal charges calculated to determine optimal structures

  • Dominant Lewis structure has formal charges closest to zero, with negative formal charge on the most electronegative atom

Resonance Structures

  • Molecules like ozone require multiple Lewis structures for accurate description

Exceptions to the Octet Rule

  1. Molecules with an odd # of valence electrons

  2. When an atom has less than an octet

  3. Atom that has more than an octet

    • Examples: Sulfur, phosphorus, silicon, and chlorine

  • Elements in periods 3 through 6 can utilize d-orbitals for more than four bonds

Bond Enthalpies

  • Bond breaking is endothermic, and bond energies vary among compounds

  • Double and triple bonds are stronger and shorter than single bonds

Types of Bonds

Ionization energy

  • Energy required to remove an electron, which forms a positive ion (cation)

Electron Affinity

  • The energy released when an electron is added to a neutral atom to form an anion (Negative charge)