Lecture Notes Review on Covalent Bonding and Lewis Structures

Covalent Bonding

Types of Bonds

  • Covalent Bonds: Formed between nonmetals, characterized by the sharing of electron pairs.

  • Ionic Bonds: Occurs between metals and nonmetals, involves the transfer of electrons.

  • Metallic Bonds: Involve the pooling of electrons among a lattice of metal atoms.

Characteristics of Covalent Bonds

  • Electrons are shared rather than transferred.

  • Attractive force due to the electrostatic forces between atoms and shared electrons.

  • Typically occurs between nonmetals; covalent bonds help achieve a noble gas electron configuration.

Formation of Covalent Bonds

  • The shared electron pair is referred to as a covalent bond.

  • Atoms share electrons until each achieves a stable electron arrangement, commonly following the octet rule, which states that atoms tend to have eight electrons in their valence shell.

Single, Double, and Triple Bonds

  • Single Bond: Involves one shared pair of electrons.

  • Double Bond: Involves two shared pairs of electrons, as in:
    O=O.

  • Triple Bond: Involves three shared pairs of electrons, as in:
    N riangleright N.

Properties of Covalent Bonds

  • Bond Order: Indicates the number of electron pairs shared by two atoms.

  • Bond Energy: Energy required to break a bond; higher bond order correlates with higher bond energy.

  • Bond Length: Distance between the nuclei of two covalently bonded atoms; shorter lengths typically indicate stronger bonds.

  • Trends in bond lengths show that triple bonds are shorter than double bonds, which in turn are shorter than single bonds.

Bond Types Based on Electronegativity

  • Non-polar Covalent Bond: Electrons are shared equally.

  • Polar Covalent Bond: Electrons are shared unequally, creating partial charges.

  • Ionic Bond: Involves completely transferring electrons between atoms.

Electronegativity (EN)

  • Definition: A measure of the ability of an atom to attract electrons within a bond.

  • Trends in Electronegativity:

    • Fluorine is the most electronegative element.

    • Electronegativity decreases down a group and increases across a period, adhering to the periodic trends.

Electron Density and Bond Polarity

  • Electron Density Maps: Visual representations show charge distribution; red represents negative density while blue represents positive.

  • Dipole Moment: A measure of a bond’s polarity within a molecule, indicated by the arrow pointing toward the more electronegative element.

Water and Polar Covalent Bonds

  • Water contains two polar covalent bonds.

    • Oxygen is electron-rich (b4-), while hydrogen is electron-deficient (b4+).

    • The net dipole moment is directed toward the oxygen atom.

Drawing Lewis Structures

Purpose of Lewis Structures

  • Lewis structures illustrate valence electron distribution and aid in understanding molecular bonding and molecular shapes.

Steps to Create a Lewis Structure

  1. Determine placement of the central atom (lowest EN; if similar, use a unique one).

  2. Add other atoms and calculate the total number of valence electrons.

  3. Draw single bonds, subtracting 2 electrons for each bond.

  4. Distribute remaining valence electrons to fulfill the octet rule (2 electrons for H).

  5. Form multiple bonds if necessary.