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November 11, 2009

November 11, 2009. EXAM #3 Correction- Check OWL Chapter 8 Homework posted Today’s Topic: Lewis Structures (Sec. 8.2) Bond Properties (Sec. 8.3). Why does a covalent bond form?. The valence electrons on two atoms are attracted to one another

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November 11, 2009

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  1. November 11, 2009 EXAM #3 Correction- Check OWL Chapter 8 Homework posted Today’s Topic: Lewis Structures (Sec. 8.2) Bond Properties (Sec. 8.3)

  2. Why does a covalent bond form? • The valence electrons on two atoms are attracted to one another • The nuclei of two atoms are attracted to one another • The valence electrons on one atom are attracted to the nucleus of another atom • The repulsive forces between the protons in two nuclei and between the electrons in two atoms are strong

  3. Last time… • Bonds form when the balance of forces favors bond formation • Valence electrons are those in the outermost shell (highest n-level) • Lewis structures are used to show the valence electrons • Elemental symbol = core (nucleus + inner electrons) • Lines = bonding electrons • Dots = electrons not involved in a bond

  4. Rules for Drawing Lewis Structures • Write the skeletal structure • Add up the total # of valence electrons • Draw a bond between the central atom and each surrounding atom • Add lone pairs to the outer atoms to complete their octets • Add remaining electrons to central atom • If central atom does not have an octet, “borrow” electrons from other atoms (make double/triple bonds)- DO NOT ADD ELECTRONS (F and Cl do not form multiple bonds; C, N, O, P, and S do) • Sometimes you can’t complete an octet (B and Be)

  5. How many total bonding electrons does an acetate ion have? • 7 • 8 • 10 • 12 • 13 • 14 • 15

  6. Examples NF3 CH2Cl2 Try this one at home! CO2 O3

  7. Draw the Lewis structure for SO3. How many lone pairs does it have? • 2 • 4 • 6 • 8 • 10

  8. What does the Lewis Structure for N2 look like?

  9. Exceptions to the Octet Rule • H (2) • Be (4) • B (6) • Large elements with available d orbital SF4 BF3 ClF5

  10. Organic Structures • CH3CH3 • CH3CN • CHCCHCH2

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