L7.1: Lewis Electron-Dot Symbols

• Bonding is the joining of two atoms in a stable arrangement. Elements will gain, lose, or share electrons to reach the electron configuration of the noble gas closest to them in the periodic table.
• There are two different kinds of bonding: Ionic bonds result from the transfer of electrons from one element to another. Covalent bonds result from the sharing of electrons between two atoms.
• Ionic bonds form between:

  •A metal on the left side of the periodic table.

  •A nonmetal on the right side of the periodic table.
• Covalent bonds are formed when two nonmetals combine, or when a metalloid bonds to a nonmetal. A molecule is a discrete group of atoms that share electrons.
• For a metal, the total number of dots in the Lewis symbol is the number of electrons the atom loses to form a cation.
• For a nonmetal, the number of unpaired dots equals

  • the number of electrons the atom gains to form an anion
  • or the number it shares to form covalent bonds.
• The octet rule states that when atoms bond, they lose, gain, or share electrons to attain a filled outer level of 8 electrons (or 2, for H and Li).