6/13/2015 One Point Quiz  One quiz per table, list everyone’s name  Agree on an answer  You have two minutes

Formal Charge Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology

6/13/2015 Formal Charge The formal charge is the net charge on each atom. Assume bonding electrons belong 1/2 to each bonding atom. H C H HO H

6/13/2015 Formal Charge formal charge unshared electrons = e – donated - e – shared 2 - formal charge of oxygen 6 valence electrons = 4/2 shared electrons -- 4 unshared electrons H C H HO H

6/13/2015 C O H H H H 4 - 8/2 - 0 = /2 - 0 = /2 - 4 = 0 Formal Charges of Atoms Methanol Formal charge = valence electrons - electrons shared/2 - electrons not shared C: 4 - 8/2 - 0 = 0 H: 1 - 2/2 - 0 = 0 O: 6 - 4/2 - 4 = 0 Atoms with low formal charges generally indicate the correct bonding pattern of chemically stable molecules.

6/13/2015 Incorrect Diagrams for Methanol O H H H CH C: 4 - 6/2 - 2 = -1 H: 1 - 2/2 - 0 = 0 O: 6 - 6/2 - 2 = +1 Validity Check The sum of the formal charges always equals the charge on the molecule or ion. H C HO H H C: 4 - 4/2 - 4 = -2 H: 1 - 2/2 - 0 = 0 O: 6 - 8/2 - 0 = +2 What are the formal charges for each atom in the following structures? Validity Check The sum of the formal charges always equals the charge on the molecule or ion.

6/13/2015 Incorrect Diagrams for Methanol O H H H CHH C HO H H C: 4 - 4/2 - 4 = -2 H: 1 - 2/2 - 0 = 0 O: 6 - 8/2 - 0 = +2 C: 4 - 6/2 - 2 = -1 H: 1 - 2/2 - 0 = 0 O: 6 - 6/2 - 2 = +1 O H H H CH If either of these structures was stable, which one would more likely be stable?

6/13/2015 CN Cyanide Ion N 5 valence e – total 10 valence e – C 4 valence e – 5 e – pairs Skeleton diagram What are the formal charges for each atom in this ion? CN charge 1 e – Convert to a Lewis Dot diagram C: 4 - 6/2 - 2 = -1 N: 5 - 6/2 - 2 = 0 total charge = -1 Lewis Dot diagram

6/13/2015 Cyanide Ion C: 4 - 6/2 - 2 = -1 N: 5 - 6/2 - 2 = 0 total charge = -1 CN Which “end” of cyanide ion is negative? CN Cyanide ion reacts with iron(III) ion to make the hexacyanoferrate(III) ion. Does the iron(III) ion bond to carbon or nitrogen?

6/13/2015 Hexacyanoferrate(III) ion Fe C N C N C N C N C N N C 3- Carbon is the negative end of the cyanide ion.

6/13/2015 Ammonium Ion Nitrogen usually forms 3 bonds NHH H H + N 5 valence e – total 8 valence e – H 4 valence e – charge -1 e – Skeleton diagramLewis Dot diagram 4 e – pairs N HH H H + H: 1 - 2/2 - 0 = 0 N: 5 - 8/2 - 0 = +1 total charge = +1 Which atoms have a non-zero formal charge? In an ion, some atom must have a non-zero formal charge. Why?

6/13/2015 Formal Charges  What are the formal charges on the atoms in hydroxide ion hydronium ion (oxonium ion)

6/13/2015 Chlorate Ion Cl-O-O-O – – O O O Cl Skeleton diagram two possibilities usually the unique atom is in the center chain structures are uncommon correct structure

6/13/2015 Chlorate Ion O 18 valence e – total 26 valence e – charge 1 e – Cl 7 valence e – Only 6 electrons shown (3 pairs) O O O Cl Skeleton diagramLewis Dot diagram 13 e – pairs O O O Cl Cl: 7 - 6/2 - 2 = +2 O: 6 - 2/2 - 6 = -1 total charge = -1 O: 6 - 2/2 - 6 = -1 Why is chlorate ion a good oxidizing agent? Complete the Lewis Dot diagram

6/13/2015 Perchlorate Ion O 24 valence e – total 32 valence e – charge 1 e – Cl 7 valence e – Only 8 electrons shown (4 pairs) O OCl O O Skeleton diagramLewis Dot diagram 16 e – pairs O O O O Cl Cl: 7 - 8/2 - 0 = +3 O: 6 - 2/2 - 6 = -1 total charge = -1 O: 6 - 2/2 - 6 = -1 Why are organic perchlorate salts potentially explosive?

6/13/2015 Pair Activity Formal Charges  Develop a procedure to determine the formal charges on a molecule or ion. Initially, one person should be responsible for writing all the information. The other person should be responsible for saying what should be written.

6/13/2015 Pair Activity Formal Charges  On a card or a piece of paper write each sequential step necessary to determine the formal charges. number each step. amend and update the list.  Determine the formal charges on acetic acid, CH 3 COOH acetate ion, CH 3 COO –

6/13/2015 Acetic Acid and Acetate Ion O H C H H H C O O O C H H H C O C H H H C O C: 4 - 8/2 - 0 = 0 total charge = 0 H: 1 - 2/2 - 0 = 0 O: 6 - 4/2 - 4 = 0 C: 4 - 8/2 - 0 = 0 total charge = -1 H: 1 - 2/2 - 0 = 0 O: 6 - 2/2 - 6 = -1 O: 6 - 4/2 - 4 = 0

6/13/2015 Formal Charges  What are the formal charges on the atoms in ozone sulfite ion sulfur trioxide

6/13/2015 “Connection” diagram Convert to a Lewis Dot diagram Carbonate Ion charge 2 e – O 18 valence e – total 24 valence e – C 4 valence e – O O O C 2- O O O C 2- Lewis Dot diagram 12 e – pairs Which oxygen atom has the double bond?

6/13/2015