Bonding

Chemical Bonding Types

  • Chemical bonds are lasting attractions between atoms that enable formation of chemical compounds.
  • Three primary types of bonds: Ionic, Covalent, and Metallic
  • Ionic bonding involves complete transfer of electrons from one atom (metal) to another (non-metal). The metal becomes a positive ion and the non-metal becomes a negative ion.
  • Covalent bonding involves the sharing of electrons between non-metal atoms. The shared electrons count for both atoms, fulfilling the octet rule.
  • Metallic bonding is the force of attraction between valence electrons and the metal ions. The valence electrons are free to move and are often referred to as a ‘sea of electrons’.

Features of Ionic and Covalent Compounds

  • Ionic compounds: high melting and boiling points, conducts electricity when molten or in solution, usually soluble in water, usually form crystals.
  • Covalent compounds: low melting and boiling points, poor conductors of electricity in all states, may be soluble or insoluble in water, often non-crystalline.

Shapes of Molecules

  • The shape of a molecule is determined by the VSEPR (Valence Shell Electron Pair Repulsion) Theory. The shape corresponds to the way that pairs of valence electrons arrange themselves around a central atom.
  • Common shapes include linear, bent, trigonal planar, trigonal pyramidal, and tetrahedral.

Polarity and Electronegativity

  • Polarity is determined by the difference in electronegativity between atoms in a bond.
  • Electronegativity is the measure of the tendency of an atom to attract a bonding pair of electrons.
  • In a molecule, if the electronegativity difference is large, the bond is ionic. If it’s small, the bond is covalent, and if the difference is zero, the bond is non-polar covalent.

Intermolecular Forces and States of Matter

  • Intermolecular forces refer to forces of attraction between molecules. The stronger the intermolecular force, the higher the melting or boiling point.
  • Van der Waals’ forces encompass all type of momentary or induced dipole interactions and are present in all molecules, whether polar or non-polar.
  • Dipole-dipole forces are attractive forces between the positive end of one polar molecule and the negative end of another polar molecule.
  • Hydrogen bonding is a special type of dipole-dipole interaction that occurs when a hydrogen atom bonded to a highly electronegative atom exists in the vicinity of another electronegative atom with a lone pair of electrons.

Understanding Hybridization

  • Hybridization is the concept of mixing atomic orbitals into new hybrid orbitals suitable for the pairing of electrons to form chemical bonds.
  • It helps explain molecule shape, since the angles between bonds are approximately equal to the angles between orbitals.
  • The type of hybridization (sp, sp2, sp3) depends upon the type of bonds and lone pairs around the central atom.