Covalent Bonding - Quick Reference

Covalent Bonding

  • Covalent bonds are formed by the sharing of valence electrons between non-metal atoms.
  • Each atom achieves a full valence shell, usually 88 electrons.
  • The covalent molecule is neutral; ions are not formed.
  • Bonding occurs between non-metals; other types of bonding exist: metallic bonding (between metals) and ionic bonding (metal + non-metal).
  • Covalent bonds can be single, double, or triple depending on the number of electron pairs shared.

Bonding Types

  • Metallic bonding: between metal atoms
  • Ionic bonding: between metal and non-metal
  • Covalent bonding: between non-metals
  • There are different types of bonding.

Representations of Covalent Bonding

  • Structural Formula: bonds are lines; each bond contains 22 electrons (one pair); a single bond is one line, a double bond is two lines.
  • Electron Shell Diagrams: show only valence electrons; electrons drawn as dots or crosses.
  • Covalent bonds can be single, double, or triple; number of lines indicates bond type.

Examples of Covalent Molecules

  • H2 and Cl2: single bonds
  • H2O: two single bonds (H-O-H)
  • O2: double bond (O=O)
  • NH3: three single bonds
  • CH4: four single bonds (C with four H)

How Atoms Achieve Stability

  • Non-metals need to gain electrons to achieve a full valence shell, usually to fill to 88 electrons.
  • When two non-metals react, they share electrons instead of transferring them.
  • No ions are formed; the result is a covalent molecule (a neutral entity).

Diatomic Molecules & Noble Gases

  • A diatomic molecule consists of two non-metal atoms covalently bonded (di means two); examples: H2, N2.
  • Noble gases (group 18) have full valence shells and are inert; they are monatomic (He, Ne, Ar).

Properties of Covalent Molecules

  • Low melting & boiling points; many are gases at room temperature.
  • Non-conductive in any state; covalent molecules do not form ions.
  • Soft or brittle (varies by substance).

Why Low MP & BP

  • Melting/boiling breaks intermolecular forces, which are weak; covalent bonds remain intact and require much more energy to break.

Covalent Networks

  • Some substances form covalent networks (e.g., diamond, silica); no discrete molecules; strong covalent bonds throughout; different properties; studied next year.