Covalent Bonds Covalent bonds - Elements sharing electrons to form a bond. Lewis Structures use Electron Dot Diagrams to show how electrons are arranged in molecules.

• • -- • ,on ,on atoms SHAR ING OF ELECTRONS TRA NSFER OF ELECTRON -- • po.sitive neg.ative molecule ,on ,on covalent bond

Strength of Bonds Higher number of bonds between 2 atoms corresponds to shorter bond lengths, and, in general, to stronger bonds.

Drawing Lewis Structures Arrange the atoms (Dot Diagrams). The LEAST electronegative atom is central in the model (except Hydrogen). Electronegativity increases left to right and bottom to top. The central atom is often the 1st atom in the formula. Carbon is ALWAYS central. Hydrogen/halogens are always terminal (on end).

Drawing Lewis Structures Form bonds: A dash (—) represents 1 pair of shared electrons. A colon (:) equals a lone pair of electrons (non-bonding electrons). Hydrogen can form only 1 bond since it only needs 2 e- to be stable.

Drawing Lewis Structures 3. If central atom is not yet surrounded by 4 electron pairs or does not form an octet, convert one or more of the lone pairs from a terminal atom into double or triple bonds. • This will only happen with C, N, O, P, or S.

Practice Draw the Lewis structures for the following. Cl2 HBr H2S CCl4 PH3

Practice Draw the Lewis structures for the following. O2 CH4 N2 N2O H2O