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Unit 6 Molecular Geometry and Polarity

Unit 6 Molecular Geometry and Polarity . Overview of bond types: i onic c ovalent metallic. Water Why bent shape? Why important? Why does NaCl dissolve in water? Why polar?. Electrostatic attraction + -. Between nuclei and e- clouds e- that satisfy octet rule stick around b/c of +-

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Unit 6 Molecular Geometry and Polarity

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  1. Unit 6 Molecular Geometry and Polarity Overview of bond types: ionic covalent metallic

  2. Water Why bent shape? Why important?Why does NaCl dissolve in water?Why polar?

  3. Electrostatic attraction + - • Between nuclei and e- clouds • e- that satisfy octet rule stick around b/c of +- • Chemical bond result of e.a. between nuclei and e- • Bond contains energy- E needed to break • Forces- attractive between atoms • Repulsion- between e- in bonding atoms and charged nucleus

  4. Bond formation • Valence e- only • At highest energy level • Use PT to determine valence • Bonds- result in octet rule satisfaction • All atoms want to be NOBLE • Which periods of atoms want to be which NOBLES?

  5. RESULT: • Lowest potential energy • Process of bonding- exothermic • Energy released • IF E released is large then = strong bond • Small E release= weak bond

  6. For valence e- only • Ionic - transfer of e- • Covalent- sharing of e- • Metallic- free e-

  7. Valence e- Transfer, shared and free All to get to octet.. All atoms want to be NOBLE

  8. Lewis Structures and Symbols • Chemical symbol represents nucleus and core electrons • Dots are valence e- Si

  9. Your Turn PT Table orbital tab • Do • Nitrogen • Phosphorus • Arsenic • Antimony • Notice anything?

  10. Try me… P As Sb Bi

  11. Lewis Dot Structures in bonding

  12. Lewis structures show presence of all valence electrons in a compound. • If ionic, metallic or covalently bonded compounds may all be represented. • This unit concentrates on covalently bonded molecular compounds but ionic compound representation is required.

  13. Metallic Bonds also crystal lattice • Ions fixed • Valence e- free • Ionic bonds Na + Cl

  14. Covalent bonds • Do Lewis dot structures for HCl H + Cl

  15. Non polar F F diagram.. No charge separation Pull of val e- is =

  16. Polar • Unequal pull H Cl Cl EN is greater than H so Cl pulls more strongly H b/comes more + as e- pulled more towards Cl Unequal sharing use lower case delta ᵟ

  17. Can do EN calculation ᵟ+ H Cl ᵟ- The greater difference in EN, the more likely loss of e- and ionic 0-.3 .3to 1.00 1.00 to 1.7 more than 1.7

  18. Ionic transfer of v e- • Metallic free v e-

  19. Another ionic compound One e- from Ca atom may be given to each fluorine atom to satisfy octet rule

  20. Lewis Structure for CaF2

  21. Your Turn • Sodium Chloride • Iron II flouride • Potassium Bromide

  22. Covalent compounds and polyatomic ions can be described by • Molecular formula: kind/types numbers of atoms but give no information of bonds connectivity

  23. Structural formula: depicts arrangement of atoms in space But gives no information regarding arrangement of valence electrons

  24. Lewis Structures Does … • Shows valence e- arrangement • Lewis structures written for molecules that obey Octet Rule! • (exceptions: deficiency, extended and odd#)

  25. Lewis Dot Diagram Rule 1: • Count valence e- of each atom • Add totals for all atoms • Make adjustment for charge if any • (-1 charge add e- +2 charge 2 less e-)

  26. Rule 2: • Arrange atoms in the diagram as follows: • Choose least EN atom as central atom- usually atom closest to left side of PT or largest • Arrange other atoms around central atom (CA) • Hydrogen can only form one bond- never CA • Carbon has 4 single bonds except in CO and CN (Has 3 bonds and unshared v e- pair)

  27. Rule 2 continued… Arrange other atoms around central atom (CA) Hydrogen can only have one bond, why? Carbon has 4 single bonds except CO and CN-1

  28. Your Turn… Calculate val e- and organize CA and outside atoms in the following: Carbon dioxide Ammonia Carbon tetrachloride Methane Carbon ion Ammonium ion

  29. Rule 3 • Place vale e- around CA as follow: • Connect outer atoms to CA with single covalent bond- each bond takes 2 e- • Calculate # of remaining val e- • Fill octets of outer atoms • Place any remaining e- on CA

  30. Rule 4 • Check CA if Octet Rule satisfied • IF NOT- make multiple bonds double or triple • (this done by moving unshared e- pair on outer atom to CA • ONLY FEW ELEMENTS CAPABLE OF FORMING MULTIPLE BONDS: c n o p s • AND RARE-chlorine

  31. Your Turn.. Return to these diagrams Add val e- Make Lewis Structures for each Carbon dioxide Ammonia Carbon tetrachloride Methane Carbon ion Ammonium ion

  32. exception NH4+ nonmetals form this cation Only polar atomic ion formed by two nonmetals

  33. exceptions to octet rule?

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