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Lewis Structures. Lewis Structures. How the atoms in covalent compounds are hooked together. Similar to Lewis Dot Diagrams Must follow a set of rules to get the Lewis Structure. The RULES. 1. Add up the number of valence electrons in the compound
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Lewis Structures • How the atoms in covalent compounds are hooked together. • Similar to Lewis Dot Diagrams • Must follow a set of rules to get the Lewis Structure
The RULES 1. Add up the number of valence electrons in the compound 2. Guess at a structure and hook the atoms together using single bonds A) Usually the first element is in the middle B) Usually the most metallic element is in the middle 3. Give all atoms on the outside an octet 4. If you have electrons left over after step 3 then add all of them to the central atom 5. If you don’t have enough electrons to give the central atom an octet A) Check for deficient atoms (Be, B, Al) B) Try a double bond C) Try a triple bond
HINTS • Leave a big gap in your notes for a list of hints
Practice Problems • Carbon tetrachloride • CCl4 • HINT: Carbon is almost always in the middle
Practice Problems • Ammonia • NH3 • HINT: Hydrogen only needs two electrons to get an “octet”
Practice Problems • Sulfur hexafluoride • SF6 • HINT: Some central atoms can have more than an octet of electrons. S and P do this often.
Practice Problems • Boron trihydride • BH3 • There is no way Boron can have an octet • HINT: Boron, Beryllium, and Aluminum very rarely have an octet of electrons.
Practice Problems • Formaldehyde, CH2O • Which structure is correct? • HINT: The most symmetric structure is usually the correct one.
Practice Problems • Hydrogen cyanide, HCN
Practice Problems • Nitrate ion
Practice Problems • Acetylene, C2H2
Practice Problems • Carbon dioxide
Practice Problems • R-134a, CF3CH2F
Practice Problems • Nitrite ion