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WHAT ARE LEWIS STRUCTURES?. Lewis structures model the electron arrangement in molecules using electron-dot notation. Pairs of dots or lines represent bonding pairs. STEPS TO DRAWING LEWIS STRUCTURES. Count the total number of valence electrons
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WHAT ARE LEWIS STRUCTURES? • Lewis structures model the electron arrangement in molecules using electron-dot notation. Pairs of dots or lines represent bonding pairs.
STEPS TO DRAWING LEWIS STRUCTURES • Count the total number of valence electrons 2. Arrange the atoms to form a “skeleton” for the molecule. If carbon is present, it is ALWAYS the central atom. 3. Add unshared electron pairs so that each atom is stable. 8 around each atom EXCEPT hydrogen which only holds 2 electrons
Count the electrons in the Lewis structure to be sure that the valence electrons used equals the number available. • If too many electrons have been used, subtract one or more LONE pairs until the total number of valence electrons is correct. Then move one or more lone pairs to existing bonds between NON hydrogen atoms.
LETS PRACTICE • Determine the electron dot notations for the following atoms: H As N P Al S O Se Br Cl Kr I K He Si
Determine the Lewis Dot Structures for Each molecule • BeF2 • HCl • CCl4 • SiO2 • NH3 • HF • Br2 • H2O
Now Determine the Lewis Structures for each of the above • Hint: Use dashes instead of dots.
Finally, determine the more negative atom in each of the above molecules 1. 2. 3. 4. 5. 6. 7.
Warm-up Drawing Lewis Structures: Page 272 (99-100)
PAGES 256-257 • Group Assignment: • Read the text pages above and describe the terms “resonance” and “expanded octet” to each member of your table. Answer questions 101 -104 on page 273 of text