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Intersection 4

M. Intersection 4. 9/26/06 Reading: 8.6 bond length p 348-351 8.10 exceptions p 363-366. The Cutting Edge Science at the Extent of our Knowledge Oct 9 th 6:00 – 7:30 PM Information Storage: DNA and Transistors Attendance Optional. M. Outline. Concept Questions Lewis Structures

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Intersection 4

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  1. M Intersection 4 9/26/06 Reading: 8.6 bond length p 348-351 8.10 exceptions p 363-366 The Cutting Edge Science at the Extent of our Knowledge Oct 9th 6:00 – 7:30 PM Information Storage: DNA and Transistors Attendance Optional

  2. M Outline • Concept Questions • Lewis Structures • Bond Length • Ethics

  3. M Question 1 What is the approximate number of carbon atoms it would take placed next to each other to make a line that would cross this dot: • • 4 • 200 • 30,000,000 • 6.02 x 1023

  4. A Question 2 Following is a list of properties of a sample of solid sulfur: • Brittle, crystalline solid. • Melting point of 113oC. • Density of 2.1 g/cm3. • Combines with oxygen to form sulfur dioxide Which, if any, of these properties would be the same for one single atom of sulfur obtained from the sample? • i and ii only. • iii and iv only. • iv only. • All of these properties would be the same. • None of these properties would be the same.

  5. M Find the Molecular Weight of: Methane CH4 C 12.011 g/mol (*1) H 1.007 g/mol (*4) CH4 16.039 g/mol Cholesterol C27H46O

  6. M Question 3 Which of the following are true about 18.013 grams of water H2O : a) Contains 2 hydrogen atoms and 1 oxygen atom b) Contains 2 moles of hydrogen atoms and 1 mole of oxygen atoms c) Contains 1 mole of water molecules d) Is 66.7% hydrogen by weight e) Contains 6.02 x1023 water molecules

  7. M Question 4 Which of the following samples could be methane, CH4?  A sample that contains: (a) 25% hydrogen by weight; 75% carbon by weight (b) 4.0 g of H atoms and 1.0 g of C atoms (c) 0.40 mole of H atoms and 1.0 x 1023 C atoms (d) 0.40 mole of H2 molecules and 0.20 moles of C atoms

  8. A Question 5 True or False? When a match burns, some matter is destroyed. • True • False What is the reason for your answer to question 3? • This chemical reaction destroys matter. • Matter is consumed by the flame. • The mass of ash is less than the match it came from. • The atoms are not destroyed, they are only rearranged. • The match weighs less after burning.

  9. Lewis Structures H3O+ Formal charge = # valence electrons -# assigned electrons Count valence electrons: H 3 * (1) = 3 O 1 * (6) = 6 - 1 8 valence e- Assigned electrons: Nonbonding electrons + 1 e- from each bond Sum of formal charges = charge of molecule

  10. SCN- Note: Usually central atom is least electronegative 16 valence e- N 3.0; S 2.5

  11. Rules for Lewis Structures • Count valence electrons • Select central atom; draw in bonds to connect atoms • Fill octets with remaining electrons • If octets cannot be filled, increase bond order • Repeat octet filling and bond order increase until satisfied • Minimize formal charges • Double check

  12. A Draw the Lewis Structure for Cyanate NCO- • Formal charge rules • The smaller the better • Negative formal charges should reside on the more electronegative atom • Avoid like charges on adjacent atoms

  13. Bond Order 1.5 1.33

  14. A Is there more than one Lewis structure for SO4-2?

  15. A Draw the Lewis Structures for the Following Molecules • BH3 • SF6 • PCl5 • NO

  16. A Group 3

  17. A Expanded Octet An expanded octet can be achieved with atoms that have d-orbitals in their valence shell.

  18. A You must have an atomic orbital in the valence shell for every bond that you make. You may not use all valence atomic orbitals to make a bond (ex, borane, water, sulfur hexafluoride.)

  19. A Radicals

  20. A Exam 1 • Tuesday, October 3 • 8-10pm CHEM 1400 • Material through Friday 9/29 • Non-programmable calculator • Practice problems posted on-line

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