4/4/2013 1 Mr. Sudbury You must know the number of valence electrons for each atom. (Pattern on PT) (Pattern on PT) (Pattern on PT) (Pattern on PT) Electron Electron Electron Electron- - -dot notation dot notation dot notation dot notation can also be used to represent molecules. Lewis Structures Lewis Structures Lewis Structures Lewis Structures – Formulas in which atomic symbols represent nuclei and inner-shell electrons, dot pairs or dashes represent electron pairs SHARED in covalent bonds H 2 F 2 A single bond is a covalent bond produced by the sharing of one pair of electrons between atoms The electrons that are not used in bonding are called the unshared pair or lone pair. C 2 H 4 A double bond is a covalent bond produced by the sharing of two pairs of electrons between atoms N 2 A triple bond is a covalent bond produced by the sharing of three pairs of electrons between atoms VSEPR VSEPR VSEPR VSEPR – “Valence Shell Electron-Pair Repulsion” VSEPR Theory VSEPR Theory VSEPR Theory VSEPR Theory states that the repulsion between the sets of valence-level electrons surrounding an atom causes these sets to be as far apart as possible. VSEPR explains VSEPR explains VSEPR explains VSEPR explains why compounds take the shape they do. (Their molecular geometry.)