Lewis dot structure

• Lewis Dot Structure is also known as Electron Dot Structure or Lewis Structure
• It describes the chemical bonding of atoms in a molecule
• Named after Gilbert Newton Lewis
• Consists of the chemical symbol for an element surrounded by dots representing its valence electrons
• For an anion, increase the number of available electrons by the charge of the anion
• For a cation, decrease the number of available electrons by the charge of the cation
• Lewis Structure for Calcium atom:

  • Valence electrons: 2
  • Lewis Structure for Calcium cation: 0
• Lewis Structure for Sulfur atom:

  • Valence electrons: 6
  • Lewis Structure for Sulfide anions: 8
• Octet rule: Atoms tend to gain, lose, or share electrons to have eight electrons in the valence shell or attain the same number of electrons as the noble gas nearest to them in the periodic table
• Noble gases are known as stable elements due to their lack of reactivity
• Exceptions to the octet rule:

  • Does not generally apply to d or f electrons
  • Only s and p electrons are involved in the octet rule
• Lewis Structure of Water Molecule:

  • H atoms: 1 valence electron each
  • O atom: 6 valence electrons
  • Total valence electrons: 8
  • Central atom: O
  • Attached atoms: 2 H atoms
  • Combination of the atoms to form the molecule
• Covalent bonds can be classified into:

  • Single covalent bond
  • Double covalent bond
  • Triple covalent bond
• Single Covalent Bond:

  • Formed by sharing one pair of electrons
  • Represented by one dash (-)
  • Example: HCl
• Double Covalent Bond:

  • Formed by sharing two pairs of electrons
  • Represented by two dashes (=)
  • Example: CO2
• Triple Covalent Bond:

  • Formed by sharing three pairs of electrons
  • Represented by three dashes (≡)
  • Example: N2
• Exceptions to the octet rule:

  • When there are an odd number of valence electrons (e.g., Nitric Oxide)
  • When there are too few valence electrons (e.g., Be, Al, B)
  • When there are too many valence electrons (e.g., PCl5)
• Formal Charge:

  • Charge assigned to an atom in a molecule
  • Calculated as: # valence electrons - (no. of bonded electrons + no. of unbonded electrons)
• Transcendental function