Lewis Structures visualize molecular structure assume most atoms

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Lewis Structures visualize molecular structure assume most atoms will have octet of electrons 1.

Lewis Structures visualize molecular structure assume most atoms will have octet of electrons 1. Determine number of valence electrons 2. Place least electronegative atom at center 3. Using e- pairs, bond central atom to surrounding atoms 4. Complete octets on surrounding atoms 5. Place remaining e- on central atom. Use multiple bonds to complete octet, if necessary

nitrogen trifluoride NF 3 valence e- 5 + (3 x 7)= 26 e- N=

nitrogen trifluoride NF 3 valence e- 5 + (3 x 7)= 26 e- N= 5 F= 7 : : : : F : N : F : : : : : : F N F: : F : : central atom = N bond F to N complete octets surrounding atoms complete octet central atom include lone pairs 6 e 24 e 26 e-

carbonate ion valence e- CO 32 - C=4 O=6 : : : O :

carbonate ion valence e- CO 32 - C=4 O=6 : : : O : C : O: 24 e : O: 6 e- 4 + (6 x 3) = 22 echarge = 2 - 24 e- C=O bond shorter C O bond stronger : O C O resonance structures : : : O C O : : : O: : : O C O: : : O C O: O

formaldehyde CH 2 O 4 + 6 + (2 x 1) = 12 e

formaldehyde CH 2 O 4 + 6 + (2 x 1) = 12 e 4 - 0 - 4 = 0 which is best structure? H : C: : O: H formal charge 6 - 2 - 3= 1 compare e- in isolated atom to : : : : H : C: H : O : 4 - 2 - 3 = -1 : 6 - 4 - 2 = 0 e- in Lewis structure formal charge = valence e- - lone pair e- - ½ shared eformal charge = 0 preferred . . C. . . N. . . O. . .

nitric acid HNO 3 valence e- N= 5 O =6 oxy acid O-H :

nitric acid HNO 3 valence e- N= 5 O =6 oxy acid O-H : : O: N : O : H : O: : : 0 +1 O N O H 0 -1 O complete octets surrounding atoms complete octet central atom 8 e 24 e- : H= 1 central atom = N bond O to N bond H 5 + (3 x 6) + 1 = 24 e- O N O H O -1 +1 +1 O N O H O -1

Exceptions to octet rule 1. Molecules with odd number of electrons Lewis structures electron

Exceptions to octet rule 1. Molecules with odd number of electrons Lewis structures electron pairs unpaired e- free radical : N: : O : : : N: O : start with 12 e- : : 5+6= : : NO 11 e- 5 - 4 - 2 = -1 5 - 3 - 2 = 0 6 - 3 - 2 = +1 6 - 4 - 2 = 0

Exceptions to octet rule 2. Incomplete octets (fewer than 8 e-) B Be (Al)

Exceptions to octet rule 2. Incomplete octets (fewer than 8 e-) B Be (Al) B : F: : F : : : boron trifluoride BF 3 F: 3 + (3 x 7)= 24 e-

Exceptions to octet rule : : Cl : : : P : : 3.

Exceptions to octet rule : : Cl : : : P : : 3. Expanded octet more than 8 eonly Period 3 and above must have d orbitals phosphorous pentachloride PCl 5 5 + (5 x 7)= 40 e- : Cl Cl :