Covalent Compounds and Lewis Structures

Fundamental Concepts of Covalent Compounds

• Covalent compounds are chemical compounds formed when valence electrons are shared between constituent atoms to achieve bonding.
• Covalent bonding occurs exclusively between non-metal elements.
• The bonding mechanism involves shared electron pairs positioned between nuclei, allowing each participating atom to achieve a stable, full valence electron configuration.

Representative Example: Water ($H_2O$)

• Chemical Formula: $H_2O$
• Constituent Atoms:
  • One central oxygen ($O$) atom possessing 6 valence electrons.
  • Two hydrogen ($H$) atoms, each possessing 1 valence electron.
• Electron Sharing Mechanism:
  • Oxygen requires 2 additional valence electrons to complete its valence shell octet ($8\,e^-$).
  • Each hydrogen atom requires 1 additional electron to achieve a full valence shell duet ($2\,e^-$).
  • Oxygen forms two single covalent bonds by sharing one electron pair with each of the two hydrogen atoms.
• Visual Representations:

• Lewis Electron Dot Representation:
  • Initially represented by oxygen surrounded by 6 valence dots interacting with two individual hydrogen atoms.
  • Intermediate Lewis dot structure shows shared pairs of dots between oxygen and each hydrogen atom ($H:\ddot{O}:H$).
• Structural Formula:
  • Translates shared pairs of bonding electrons into solid lines.
  • Expressed as $H-\ddot{O}-H$ (or $H-\underset{H}{\ddot{O}}:$) to show both bonding pairs and non-bonding lone pairs on the central oxygen atom.
• Bond Equivalence:
  • A single solid line dash ($-$) represents a single covalent bond.
  • One single bond line equals two shared electrons ($-\, = 2\,e^-$).

Rules for Drawing Covalent Compounds and Lewis Diagrams

• Non-metal atoms share electrons to satisfy valence shell requirements (duet rule for hydrogen, octet rule for standard non-metals).
• Shared electron pairs located between two atomic symbols constitute chemical bonds.
• In structural formulas, each single bond line ($-$) represents exactly 2 shared valence electrons ($2\,e^-$).
• Non-bonding valence electrons remaining on an atom are depicted as unshared lone pairs (electron dots).