1 / 8

Lewis Structures

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. Using e - pairs , bond central atom to surrounding atoms.

Download Presentation

Lewis Structures

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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 • 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

  2. : : : : : F F N : : : : F : nitrogen trifluoride NF3 valence e- N = 5 5 + (3 x 7) = 26 e- F = 7 central atom = N bond F to N : : : : : : : F F N 6 e- complete octets : : : : : F 24 e- surrounding atoms : 26 e- complete octet central atom include lone pairs

  3. C O bond O C O O : : : : : : : : : : O C O O C O O C O : : : : : : : : : : : : O O O : : carbonate ion CO32- 4 + (6 x 3) = 22e- valence e- C = 4 charge = 2- O = 6 24e- : : C=O bond shorter : : : : O C O 6e- stronger : : : 24e- : : O : resonance structures

  4. : . .. .. . . . . . . C N O . .. . 6 + (2 x 1) = 12e- formaldehyde 4 + CH2O 4 4 - 0 - 4 = 0 - 2 - 3 = -1 : : : : : : : which is best structure? H C H H C O H : : : : formal charge 6 - 2 - 3 = 1 O : compare e- in isolated atom to 6 - 4 - 2 = 0 e- in Lewis structure - ½ shared e- formal charge = - lone pair e- valence e- formal charge = 0 preferred

  5. O N O H O O N O H O O N O H O nitric acid HNO3 valence e- N = 5 5 + (3 x 6) + 1 = 24 e- O = 6 oxy acid O-H 1 H = : : : : : : O N O H 8 e- central atom = N : : : : : 24 e- O bond O to N : +1 0 bond H 0 complete octets -1 +1 +1 -1 surrounding atoms complete octet central atom -1

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

  7. Exceptions to octet rule 2. Incomplete octets (fewer than 8 e-) B Be (Al) boron trifluoride BF3 3 + (3 x 7) = 24e- : : : : F F B : : : F : :

  8. : : : : : Cl : : Cl Cl : : : : : : Cl Cl : : Exceptions to octet rule 3. Expanded octet more than 8 e- must have d orbitals only Period 3 and above phosphorous pentachloride PCl5 5 + (5 x 7) = 40e- P

More Related