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Lewis Dot Structures

Lewis Dot Structures. 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.

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Lewis Dot Structures

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  1. Lewis Dot Structures

  2. 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.

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

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

  5. Lewis Structure for CaF2

  6. Your Turn • Sodium Carbonate • Magnesium Chloride

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

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

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

  10. 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-)

  11. 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)

  12. 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

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

  14. 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

  15. 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

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

  17. exceptions to octet rule?

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