Lewis Structures Ac

• I can draw a Lewis structure for a given molecule

Learning Targets

• Lewis structures are a visual representation of covalent bonding that indicates where the valence shell electrons are in the molecule.

• Shared electron pairs are shown as lines and lone pairs (pairs of electrons not involved in bonding) are shown as dots.

Lewis Structures

• Atoms tend to gain, lose or share electrons until they are surrounded by eight valence electrons (octet).

• An octet consists of full s and p orbitals.

Octet Rule Revisited

• Duet RuleHydrogen bonds to have 2 valence electrons

• Boron Boron bonds to have 6 valence electrons

Exceptions to the Octet Rule

• Sum all valence electrons from atoms in the moleculesAnion – add electrons equal to the chargeCation – subtract electrons equal to the charge

Lewis Structures Rules

• Identify the central atom (least electronegative or first atom in the formula)Write the symbol for the central atom surrounded

by symbols for all other atoms bonded to the central atom


• Connect atoms with a single bond (a line representing 2 electrons) to the central atomSubtract bonding electrons from electron total


• Use remaining electrons to complete the octets of all atoms bonded to the central atomPlace any remaining electrons on central atom


• Check the octet of the central atom. Complete the central atom octet by using multiple bonds if necessary.


• PCl3

Practice ProblemsDraw Lewis structures for the following molecules.

• PCl3

Total electrons• P = 1 x 5 = 5


• PCl3

Total electrons• P = 1 x 5 = 5• Cl = 3 x 7 = 21


• PCl3

Total electrons = 26• P = 1 x 5 = 5• Cl = 3 x 7 = 21


• PCl3

Total electrons = 26• P = 1 x 5 = 5• Cl = 3 x 7 = 21


P ClCl

Cl

• PCl3

Total electrons = 26 – 6 = 20• P = 1 x 5 = 5• Cl = 3 x 7 = 21


P ClCl

Cl

• PCl3

Total electrons = 26 – 6 = 20• P = 1 x 5 = 5• Cl = 3 x 7 = 21


P ClCl

Cl..

.

.

.

...

. .

. .

. . . .

. .

• PCl3

Total electrons = 26 – 6 = 20 – 18 = 2• P = 1 x 5 = 5• Cl = 3 x 7 = 21


P ClCl

Cl..

.

.

.

...

. .

. .

. . . .

. .

• PCl3

Total electrons = 26 – 6 = 20 – 18 = 2 – 2 = 0• P = 1 x 5 = 5• Cl = 3 x 7 = 21


P ClCl

Cl..

.

.

.

...

. .

. .

. . . .

. .

. .

• CH2Cl2


• CH2Cl2

Total electrons• C = 1 x 4 = 4


• CH2Cl2

Total electrons • C = 1 x 4 = 4• H = 2 x 1 = 2


• CH2Cl2

Total electrons • C = 1 x 4 = 4• H = 2 x 1 = 2• Cl = 2 x 7 = 14


• CH2Cl2

Total electrons = 20• C = 1 x 4 = 4• H = 2 x 1 = 2• Cl = 2 x 7 = 14


• CH2Cl2

Total electrons = 20• C = 1 x 4 = 4• H = 2 x 1 = 2• Cl = 2 x 7 = 14


C ClCl

H

H

• CH2Cl2

Total electrons = 20 – 8 = 12• C = 1 x 4 = 4• H = 2 x 1 = 2• Cl = 2 x 7 = 14


C ClCl

H

H

• CH2Cl2

Total electrons = 20 – 8 = 12• C = 1 x 4 = 4• H = 2 x 1 = 2• Cl = 2 x 7 = 14


C ClCl

H..

.

.

. .

. . . .

. .

H

• CH2Cl2

Total electrons = 20 – 8 = 12 – 12 = 0• C = 1 x 4 = 4• H = 2 x 1 = 2• Cl = 2 x 7 = 14


C ClCl

H..

.

.

. .

. . . .

. .

H

• CO2


• CO2

Total electrons• C = 1 x 4 = 4


• CO2

Total electrons• C = 1 x 4 = 4• O = 2 x 6 = 12


• CO2

Total electrons = 16• C = 1 x 4 = 4• O = 2 x 6 = 12


• CO2

Total electrons = 16• C = 1 x 4 = 4• O = 2 x 6 = 12


C OO

• CO2

Total electrons = 16 – 4 = 12• C = 1 x 4 = 4• O = 2 x 6 = 12


C OO

• CO2

Total electrons = 16 – 4 = 12• C = 1 x 4 = 4• O = 2 x 6 = 12


C OO. . . .

. .. .

. . . .

• CO2

Total electrons = 16 – 4 = 12 – 12 = 0• C = 1 x 4 = 4• O = 2 x 6 = 12


C OO. . . .

. .. .

. . . .

• CO2



C OO. . . .

. .. .

. . . .Central atom octet not satisfied!

• CO2



C OO. . . .

. .. .

. . . .Create multiple bonds by borrowing lone pairs.

• CO2



C OO. . . .

. .. .

. . . .

• CO2



C OO. . . .

. .. .

Octets on all atoms are now satisfied.

• HCN


• HCNTotal electrons• H = 1 x 1 = 1


• HCNTotal electrons• H = 1 x 1 = 1• C = 1 x 4 = 4


• HCNTotal electrons• H = 1 x 1 = 1• C = 1 x 4 = 4• N = 1 x 5 = 5


• HCNTotal electrons = 10• H = 1 x 1 = 1• C = 1 x 4 = 4• N = 1 x 5 = 5


• HCNTotal electrons = 10• H = 1 x 1 = 1• C = 1 x 4 = 4• N = 1 x 5 = 5


C NH

• HCNTotal electrons = 10 – 4 = 6• H = 1 x 1 = 1• C = 1 x 4 = 4• N = 1 x 5 = 5


C NH

• HCNTotal electrons = 10 – 4 = 6• H = 1 x 1 = 1• C = 1 x 4 = 4• N = 1 x 5 = 5


C NH. .

. .

. .

• HCNTotal electrons = 10 – 4 = 6 – 6 = 0• H = 1 x 1 = 1• C = 1 x 4 = 4• N = 1 x 5 = 5


C NH. .

. .

. .



C NH. .

. .

. .Central atom octet not satisfied!



C NH. .

. .

. .Create multiple bonds by borrowing lone pairs.



C NH. .

. .

. .



C NH . .

• NO2–


• NO2–

Total electrons• N = 1 x 5 = 5


• NO2–

Total electrons = 17• N = 1 x 5 = 5• O = 2 x 6 = 12


• NO2–

Total electrons = 17 + 1 (for charge) = 18• N = 1 x 5 = 5• O = 2 x 6 = 12


• NO2–

Total electrons = 18• N = 1 x 5 = 5• O = 2 x 6 = 12


N OO

• NO2–

Total electrons = 18 – 4 = 14• N = 1 x 5 = 5• O = 2 x 6 = 12


N OO

• NO2–

Total electrons = 18 – 4 = 14• N = 1 x 5 = 5• O = 2 x 6 = 12


N OO. . . .

. .. .

. . . .

• NO2–

Total electrons = 18 – 4 = 14 – 12 = 2• N = 1 x 5 = 5• O = 2 x 6 = 12


N OO. . . .

. .. .

. . . .

• NO2–

Total electrons = 18 – 4 = 14 – 12 = 2• N = 1 x 5 = 5• O = 2 x 6 = 12


N OO. . . .

. .. .

. . . .

. .

• NO2–

Total electrons = 18 – 4 = 14 – 12 = 2 – 2 = 0• N = 1 x 5 = 5• O = 2 x 6 = 12


N OO. . . .

. .. .

. . . .

. .

• NO2–



N OO. . . .

. .. .

. . . .

. .

Central atom octet not satisfied!

• NO2–



N OO. . . .

. .. .

. . . .

. .

• NO2–



N OO. . . .

. .. .

. .

. .

• NO2–



N OO. . . .

. .. .

. .

. .

• NO2–



Brackets are placed around the structure with the charge indicated outside of the brackets.

N OO. . . .

. .. .

. .

. .

Education

Lewis Structures Ac