04/18/23

One Point Quiz

One quiz per table, list everyone’s name Agree on an answer You have two minutes

Formal ChargeEdward A. Mottel

Department of Chemistry

Rose-Hulman Institute of Technology

04/18/23

Formal Charge

The formal charge is the net charge on each atom.

Assume bonding electronsbelong 1/2 to each bonding atom.

HC

H

H O

H

• •• •

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Formal Charge

formalcharge

unsharedelectrons= e– donated - e– shared

2-

formal chargeof oxygen

6 valenceelectrons

=4/2 sharedelectrons

- -4 unsharedelectrons

HC

H

H O

H

• •• •

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• •• •

••C OHH

HH••••

• •• •

4 - 8/2 - 0 = 0

••••

• •• •

••••

• •• •

••

• •• •

••1 - 2/2 - 0 = 0

••

6 - 4/2 - 4 = 0

• •• •

•• ••

Formal Charges of AtomsMethanol

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 thecorrect bonding pattern of chemically stable molecules.

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Incorrect Diagrams for Methanol

••O• •

• •••••H

H• •

H

• •C HC: 4 - 6/2 - 2 = -1

H: 1 - 2/2 - 0 = 0

O: 6 - 6/2 - 2 = +1Validity Check

The sum of the formal charges always equalsthe charge on the molecule or ion.

HCH O

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 atomin the following structures?

Validity CheckThe sum of the formal charges always equals

the charge on the molecule or ion.

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Incorrect Diagrams for Methanol

••O• •

• •••••H

H• •

H

• •C H HCH O

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

• •C H

If either of these structures was stable,which one would more likely be stable?

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C N

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?

C N•• ••••

charge 1 e–

•••• •• •••••• •• •••••• •••••• ••

Convert to aLewis Dot diagram

C: 4 - 6/2 - 2 = -1N: 5 - 6/2 - 2 = 0total charge = -1

Lewis Dot diagram

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Cyanide Ion

C: 4 - 6/2 - 2 = -1

N: 5 - 6/2 - 2 = 0total charge = -1

C N•• •••• ••••

Which “end” of cyanide ionis negative?

C N•• •••• ••••

Cyanide ion reacts with iron(III) ionto make the hexacyanoferrate(III) ion.

Does the iron(III) ion bond to carbon or nitrogen?

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Hexacyanoferrate(III) ion

FeC

N•• •••• ••

••CN••••••••

••

CN••••••••

••C

N •••• ••

••••

C

N

• •• •• •

• •• •

N

C•••• ••

••••

3-

Carbon is the negative end of the cyanide ion.

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Ammonium Ion

Nitrogen usuallyforms 3 bonds

NH H

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• •

• •••H H

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?

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Formal Charges

What are the formal charges on the atoms in• hydroxide ion• hydronium ion (oxonium ion)

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Chlorate Ion

Cl-O-O-O –

–

OO

O

Cl

Skeleton diagram

two possibilitiesusually the unique atom is in the center

chain structuresare uncommon

correctstructure

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Chlorate Ion

O 18 valence e–

total 26 valence e–

charge 1 e–

Cl 7 valence e–

Only 6 electronsshown

(3 pairs)

OO

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 = -1O: 6 - 2/2 - 6 = -1

Why is chlorate ion a good oxidizing agent?

Complete the Lewis Dot diagram

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Perchlorate Ion

O 24 valence e–

total 32 valence e–

charge 1 e–

Cl 7 valence e–

Only 8 electronsshown

(4 pairs)

OO Cl

OO

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 = -1O: 6 - 2/2 - 6 = -1O: 6 - 2/2 - 6 = -1

Why areorganic perchlorate salts

potentially explosive?

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Pair ActivityFormal 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.

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Pair ActivityFormal 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, CH3COOH

• acetate ion, CH3COO–

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Acetic Acid and Acetate Ion

O ••••

HCH

H

H

CO

••

••••

O ••••

••

O ••

••

CH

H

H

C

O ••••

CH

H

H

CO

••

••••

C: 4 - 8/2 - 0 = 0

total charge = 0

H: 1 - 2/2 - 0 = 0O: 6 - 4/2 - 4 = 0O: 6 - 4/2 - 4 = 0

C: 4 - 8/2 - 0 = 0

total charge = -1

H: 1 - 2/2 - 0 = 0O: 6 - 2/2 - 6 = -1O: 6 - 4/2 - 4 = 0

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Formal Charges

What are the formal charges on the atoms in• ozone• sulfite ion• sulfur trioxide

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“Connection” diagram

Convert to aLewis Dot diagram

Carbonate Ion

charge 2 e–

O 18 valence e–

total 24 valence e–

C 4 valence e–

OO

O

C

2-

O ••• •

••••O• •

• •••

••O

• •• •

••

••C

2-

Lewis Dot diagram

12 e– pairsWhich oxygen atomhas the double bond?

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