1. Chemistry Boon Date: 09/06 & 09/07 2012

2. Catalyst Ionic or Covalent? Hint: Ionic bonds form between a metal and a nonmetal. Covalent bonds form between two or more nonmetals. 1. NaCl 2. MgF 2 3. O 2 4. H 2 5. CO 2 6. CH 4 7. Ag 2 O

3. Objectives  I can explain the difference between ionic and covalent compounds and bonds.  I can draw simple Lewis structures of molecules.

4. Agenda  Catalyst  HW Review  Open Note Quiz  Lewis Dot Structures of Molecules

5. HW Review: p. 184 #23 AtomIonNoble-gas configuration of ion S – sulfur (6 v.e.)S 2- Argon – 1s 2 2s 2 2p 6 3s 2 3p 6 Be – Beryllium (2 v.e.)Be 2+ Helium – 1s 2 I – Iodine (7 v.e.)I-I- Xenon - 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 Rb – Rubidium (1 v.e.)Rb + Krypton - 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 O – oxygen (6 v.e)O 2- Neon - 1s 2 2s 2 2p 6 Sr – Strontium (2 v.e.)Sr 2+ Krypton - 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 F – Fluorine (7 v.e.)F-F- Neon - 1s 2 2s 2 2p 6 Hint: Octet Rule: Metals lose all their negatively charged valence electrons to form positive cations. Nonmetals gain enough electrons to have a full outer shell (usually to end up with 8) and form negative anions. These ions end up with the same number of electrons as the noble gas closest to them on the periodic table.

6. HW Review (p. 198 & 216)  7. Molecular compounds have low melting points and low boiling point relative to ionic substances because the atoms in a covalent compound have a strong attraction to the atoms that they share electrons with, but there is little attraction for the atoms of other nearby molecules.  10. How does the strength of a covalent bond relate to bond length?  Generally, as the bond length gets shorter, the strength of the covalent bond gets stronger.  11. How does a covalent bond differ from an ionic bond?  In an ionic bond, electrons are transferred from a metal to a nonmetal. Covalent bonds usually form between nonmetals and involve the sharing of electrons.

7. HW Review Continued  Nonpolar = electrons are shared equally  Atoms have similar electronegativities – so they pull on the electrons equally  Polar = electrons are not shared equally  Atoms have different electronegativities – so they pull on the electrons unequally  15. Ionic/Nonpolar covalent/polar covalent?  a. Na-F: ionic  b. H-I: polar covalent  c. N-O: nonpolar covalent  d. Al-O: ionic or polar covalent  e. S-O: polar covalent  f. H-H: nonpolar covalent

8. Open Note Quiz 1. What ionic compound do Ca and Br form?  Write the formula  Write the name in words 2. WRITE A PARAGRAPH USING THIS FORMAT:  Ionic compounds and covalent compounds are similar because they both  (write at least 3 similarities here)  Ionic compounds and covalent compounds are different because  Ionic compounds _______________, but covalent compounds ____________________.  (repeat for at least 3 differences)

9. Agenda  Catalyst  HW Review  Open Note Quiz  Lewis Dot Structures of Molecules

10. Lewis Dot Structures  Lewis Dot Structures show how valence electrons are arranged in atoms and molecules  Lewis dot structures for single atoms  1e-2e-3e-4e-  5e-6e-7e-8e- NaMgAlC NO FNe

11. Rules for covalent bonding  Each bond is made up of 2 electrons  Each atom wants to reach the same configuration as the noble gases  Duet rule: Hydrogen wants 2 valence electrons  Octet rule: All other atoms want 8 valence electrons  Atoms will share electrons with other atoms so that both get a full valence shell

12. Drawing Lewis Dots for Compounds  Steps:  1. Draw Lewis Dot structures for the individual atoms  Double check your numbers of valence e-  2. Put central atom in the center  3. Put other atoms around  4. Draw 2 dots between each pair  5. Fill in other dots up to 8 (except for H)  6. Replace all bonded pairs with lines CH 4 Central atom C H H HH

13. Practice Lewis Dots  NH 3  H 2 O HH H N Total electrons:NH 3 H3H3H3H3 = 3 x 1 = 3 N = 5 = 5 8

14. Practice!  CF 4  HCl  CH 2 Br 2  C 2 H 6

15. Chemistry Date: 09/06 & 09/07 2012

16. Double and Triple Bonds  What happens when the total electrons do not match up with the Lewis structure?  Example:O 2  Draw the Lewis dot structure: OO Total valence electrons: O2O2O2O2 = 2 x 6 = 12 Single bonded structure uses too many electrons!

17. Double Bonds  If the structure has too many dots, remove lone pairs from two atoms and replace with a double bond  In a double bond, the atoms share 4 electrons  Replace the bonded pairs with 2 lines OO Lone pairs

18. Double Bonds  Some atoms can have more than one double bond  Example: CO 2 Total valence electrons: O2O2O2O2 = 2 x 6 = 12 C = 4 = 4 16COO