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Unformatted text preview: Name: ___________________________________ CH101 Lewis Structures and Formal Charges ‐ Study Guide sections 9.3, 9.7 and 9.8 in the textbook Lewis Structures of Atoms (sections 9.3) Fill in the following chart. Carbon is done for you. Group Element # of valence electrons Lewis Dot Structure IA Li IIA Be IIIA B IVA C 4 . .. VA N VIA O VIIA F VIIIA Ne C . Drawing Lewis structures for Molecules and Polyatomic Ions (section 9.7) Rules: 1. Find the sum of valence electrons of ALL atoms in the polyatomic ion or molecule. a. If it is an anion, add one electron for each negative charge b. If it is a cation, subtract one electron for each positive charge. 2. Choose a central atom. The central atom is the LEAST electronegative element that isn’t hydrogen. Connect the outer atoms to the central atom using single bonds. 3. Fill the octets of the outer atoms. Almost all atoms want to have 8 valence electrons (there are exceptions). Hydrogen wants to have 2 valence electrons. 4. Fill the octet of the central atom. Atoms in the second period CANNOT have more than 8 valence electrons. However, atoms past the second period CAN have more than 8 valence electrons. These atoms are said to have an expanded octet. 5. Add double or triple bonds if necessary. 6. Make sure you use ALL of the valence electrons (not more, not less) How many valence electrons (total) are present in each of the following substances? a) SCl2 b) HCN c) SO42‐ Watch video tutorial on Blackboard Formal Charges (section 9.8) The formal charge on an atom = number of ________________ electrons – [number of ___________ electrons + ½ number of _________ electrons] Watch video tutorial on Blackboard Give some reasons why knowing the formal charges on the atoms in a structure is useful. Calculate the formal charge on each atom for CO. End of Chapter Practice Problems Tro First Edition: # 39, 53, 59, 63 Tro Second Edition: #37, 51, 59, 61, 65 answers are located in Appendix III of the textbook Take the Quiz on Blackboard 2 ...
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This note was uploaded on 11/11/2011 for the course MATH 180 taught by Professor Byrns during the Spring '11 term at Montgomery College.
- Spring '11