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Notes: Lewis Dot Structures

Chemistry Boon Date: 09/06 & 09/07 2012. Notes: Lewis Dot Structures. Catalyst. Ionic or Covalent? Hint: Ionic bonds form between a metal and a nonmetal. Covalent bonds form between two or more nonmetals. NaCl MgF 2 O 2 H 2 CO 2 CH 4 Ag 2 O. Objectives.

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Notes: Lewis Dot Structures

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  1. Chemistry Boon Date: 09/06 & 09/07 2012 Notes: Lewis Dot Structures

  2. Catalyst Ionic or Covalent? Hint: Ionic bonds form between a metal and a nonmetal. Covalent bonds form between two or more nonmetals. • NaCl • MgF2 • O2 • H2 • CO2 • CH4 • Ag2O

  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 • 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 • What ionic compound do Ca and Br form? • Write the formula • Write the name in words • 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- Na Mg Al C F Ne N O

  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 CH4 • 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 Central atom H H C H H

  13. Practice Lewis Dots • NH3 • H2O Total electrons:NH3 H N = 5 H3 = 3 x 1 = 3 H N H 8

  14. Practice! • CF4 • HCl • CH2Br2 • C2H6

  15. Chemistry Date: 09/06 & 09/07 2012 Notes: Lewis Dot Structures part 2

  16. Double and Triple Bonds • What happens when the total electrons do not match up with the Lewis structure? • Example: O2 • Draw the Lewis dot structure: Total valence electrons: O O O2 = 2 x 6 = 12 Single bonded structure uses too many electrons!

  17. Lone pairs 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 O O

  18. O C O Double Bonds • Some atoms can have more than one double bond • Example: CO2 Total valence electrons: C = 4 O2 = 2 x 6 = 12 16

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