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To do Lewis Structures:. Must be able to recognize polyatomic ionsMust be able to identify valence electronsMust be able to construct Bond framework. Periodic Table : Column numbers!. More
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1. Lewis Dot Structure Rules: Treat ions separately (e.g. NH4Cl)
Count only valence electrons
Assemble bonding framework
Fill up non-bonding electrons on
outer atoms
Fill up non-bonding electrons on
inner atoms
Calculate Formal Charge
Minimize Formal Charge
2. To do Lewis Structures: Must be able to recognize
polyatomic ions
Must be able to identify
valence electrons
Must be able to construct
Bond framework
3. Hints on Lewis Dot Structures Octet “rule” is the most useful guideline.
Carbon forms 4 bonds.
Hydrogen typically forms one bond to other atoms.
When multiple bonds are forming, they are usually between C, N, O or S.
Nonmetals can form single, double, and triple bonds, but not quadruple bonds.
Always account for single bonds and lone pairs before forming multiple bonds.
Look for resonance structures.
4. PCl3
6. Formal Charge Difference between the # of valence electrons in the free atom and the # of electrons assigned to that atom in the Lewis structure.
FC = formal charge; G.N. = Group Number
#BE = bonding electrons; #LPE = lone pair electrons
If Step 4 leads to a positive formal charge on an inner atom beyond the second row, shift electrons to make double or triple bonds to minimize formal charge, even if this gives an inner atom with more than an octet of electrons.
10. Beyond the Octet Elements in the 3rd period or higher can have more than an octet if needed.
Atoms of these elements have valence d orbitals, which allow them to accommodate more than eight electrons.
13. VSEPR Definitions Electron group –set of electrons that occupies a particular region around an atom.
Ligand – an atom or a group of atoms bonded to an inner atom
Steric number – the sum of the number of ligands plus the number of lone pairs; in other words, the total number of groups associated with that atom.
14. KNOW THESE!
15. Lone Pairs Take up a Bit More Space… Experiments show that sulfur tetrafluoride has bond angles of 86.9° and 101.5 °. Give an interpretation of these bond angles