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Lewis Dot Diagrams

Lewis Dot Diagrams. Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology. Bonding Theories. Ionic Model Skeleton Diagrams Identifies how atoms are linked together Fails to describe the bonding in ions and certain molecules (e.g., CO, NH 4 + , CN – )

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Lewis Dot Diagrams

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  1. Lewis Dot Diagrams Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology

  2. Bonding Theories • Ionic Model • Skeleton Diagrams • Identifies how atoms are linked together • Fails to describe the bonding in ions and certain molecules (e.g., CO, NH4+, CN–) • Fails to explain the geometry of molecules • Lewis Dot Diagrams

  3. 1s2 • • • • • • • • • • • • • • • • • • • • • • • • H H H H H H H H F F F F F F F F • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • H F • • • • Lewis Dot Diagrams Each dot represents an electron in the outer (valence) shell in one of the atoms. Each atom attempts to attain a stable outer shell electronic configuration by sharing electrons with other atoms. (typically a noble gas electronic configuration)

  4. 1s2 Didn’t your mother always tell you to share?

  5. isoelectronic with neon (OCTET) isoelectronic with helium (DUET) • • • • H F • • • • Lewis Dot Diagrams Each atom sharing an electron can count that electron towards attaining its stable electronic configuration. Each pair of electrons which are shared forms a bond between those atoms.

  6. Lewis Dot Diagrams • Bonding electrons may come from both atoms or they may only come from one atom. • The most stable bonding results when both atoms donate electrons to the bond.

  7. eight electrons { • • • • • C O • • • • • { total 10 valence e– eight electrons C ºO • • • • Carbon Monoxide Diagram C 4 valence e– O 6 valence e– 10 6 2 8 4 Three pairs of electrons is a triple bond. Both atoms are isoelectronic with neon.

  8. eight electrons eight electrons { { • • • • • • • • C O O • • • • { total 16 valence e– • • • • eight electrons • • • • O O C • • • • Carbon Dioxide Diagram C 4 valence e– two O 12 valence e– 16 14 12 10 8 6 4 2 Carbon dioxide has two double bonds. All three atoms are isoelectronic with neon. Draw the skeleton diagram for carbon dioxide. Determine the total number of valence e- available.

  9. eight electrons { • • • • H N H • • • • H { two electrons Ammonia Diagram N 5 valence e– three H 3 valence e– total 8 valence e– Nitrogen is isoelectronic with neon. Each hydrogen is isoelectronic with helium.

  10. eight electrons { C 4 valence e– • • • • Cl • • four Cl 28 valence e– • • • • • • • • • • Cl Cl C • • • • total 32 valence e– • • • • • • • • Cl • • • • eight electrons Carbon Tetrachloride Diagram Carbon is isoelectronic with neon. Each chlorine is isolectronic with argon.

  11. methane dioxygen ozone water hydrogen peroxide ammonium ion Draw the Skeleton Diagram andLewis Dot Diagram forEach of the Following

  12. Types of Bonds • The degree with which electrons are shared determines the type of bond that forms. • Covalent Bonds • Ionic Bonds

  13. H H H C H Covalent Bonding • Results when each atom equally shares with the other atoms the electrons in its bonds. • One pair of shared electrons equals one bond. • Occurs with atoms of about the same electronegativity.

  14. • • • • • • • • • Cl • • • • isoelectronic with neon isoelectronic with argon Occurs with atoms of greatly different electronegativity. Ionic Bonding Results when "bonding" electrons are transferred completely to one of the atoms. - + • Na atom with low electronegativity loses control of the electron atom with high electronegativity gains complete control of the electron Lewis Dot structures are more appropriate for covalent bonding.

  15. H • • H O H C • • H total 14 valence e– Methanolmethyl alcohol, wood alcohol, CH4O Skeleton diagram Lewis Dot diagram C 4 valence e– H 4 valence e– O 6 valence e– Lines or pairs of dots can be used to represent a bond. How many electrons are shown? 7 e– pairs All valence electrons are represented as bonds and nonbonding electrons

  16. H • • • • • • • H C H O • • • • • • • H Methanolmethyl alcohol, wood alcohol, CH4O Lewis Dot diagram oxygen needs 8 e– to complete its outer shell carbon needs 8 electrons to complete its outer shell of electrons (1s2 2s2 2p6) each hydrogen only needs 2 e– to complete its outer shell (1s2) Next

  17. Pair ActivityLewis Dot Structures • Develop a procedure to draw a Lewis Dot diagram. • Initially, one person should be responsible for writing all the information. • The other person should be responsible for saying what should be written. • Hint: Draw a valid skeleton diagram, and use that information to help draw the dot diagram.

  18. Lewis Dot Structures • On a card or a piece of paper • write each sequential step necessary to draw a Lewis Dot diagram. • number each step. • amend and update the list. Either person may do this. • draw the Lewis Dot diagram of acetic acid, CH3COOH.

  19. • • H H • • H H • O O • • • • • • • • • • • H C H C C C • • • • • • • • • • O O • • H H • • • • Acetic Acid

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

  21. H • • H O H C • • H Formal Charge Assume bonding electrons belong 1/2 to each bonding atom. The formal charge is the net charge on each atom.

  22. e–shared 2 H • • H O H C • • H Formal Charge unshared electrons formal charge - = e–donated - formal charge of oxygen 6 valence electrons 4/2 shared electrons 4 unshared electrons = - -

  23. 4 - 8/2 - 0 = 0 H • • • • • • • • • • • • • • • • • • • • • • • • H C H O • • • • • • • • • • • • • • • • • • • • • • • • 1 - 2/2 - 0 = 0 H 6 - 4/2 - 4 = 0 C: 4 - 8/2 - 0 = 0 H: 1 - 2/2 - 0 = 0 O: 6 - 4/2 - 4 = 0 Formal Charges of AtomsMethanol Formal charge = valence electrons - electrons shared/2 - electrons not shared Atoms with low formal charges generally indicate the correct bonding pattern of chemically stable molecules.

  24. H H • • • • • • • • • H C H H O H C O • • • • • • • • • C: 4 - 6/2 - 2 = -1 C: 4 - 4/2 - 4 = -2 H H H: 1 - 2/2 - 0 = 0 H: 1 - 2/2 - 0 = 0 O: 6 - 6/2 - 2 = +1 O: 6 - 8/2 - 0 = +2 Incorrect Diagrams for Methanol 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. Validity Check The sum of the formal charges always equals the charge on the molecule or ion.

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

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

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

  28. Formal Charges • What are the formal charges on the atoms in • hydroxide ion • hydronium ion (oxonium ion)

  29. O – O O Cl Chlorate Ion Skeleton diagram usually the unique atom is in the center two possibilities Cl-O-O-O – chain structures are uncommon correct structure

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

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

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