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UNIT 8: LEWIS STRUCTURES (Conceptual stuff (More potential energy means…
UNIT 8: LEWIS STRUCTURES
Bonding/LE
Ionic bonding: effectively transferred electrons. B/n metals and nonmetals (electroneg. difference of >1.7-2)
LATTICE ENERGY: Energy required to break apart a mole of ionic solid (lattice.) Even though ionization energy is usually more endothermic than electron affinity is exo, the attraction of opposite charges allows lattice to be favorable.
When thinking LE/bond favorability, always coulomb's law; also low ionization energy and high electron aff. is favor. bond.
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Metallic bonding: How metals bond. Like a sheet of cations and a sea of electrons. Conductive, shiny, etc.
Conceptual stuff
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ENERGY ALWAYS RELEASED WHEN BONDS ARE FORMED, AND ALWAYS ABSORBED WHEN BONDS ARE BROKEN
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Whenever oxidation state of metal increases, covalent character of bond increases
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Lewis structures --> formal charge --> if there are multiple w/equivalent formal charge, resonance
Lewis Structures
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FORMAL CHARGE:
- All unbonded, as well as in a bond but closest to the atom are assigned to that atom. (basically electrons "surrounding")
- Valence - assigned = formal charge.
Pick the structure where formal charges are closest to zero, or negative formal charges reside on more electroneg. atoms (surrounding atoms.)
RESONANCE STRUCTURES
Basically, a structure where octets can be fulfilled in multiple ways... and there isn't one "most important" structure.
The placement of the atoms in alternative but completely equivalent Lewis structures is the same, but the placement of the electrons is different
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Bond Polarity
Bonds are a on a spectrum from nonpolar to more polar (totally polar is ionic.) From more similar to sharing, to effectively transferred.
When the differences in electronegativity, or tendency to attract electrons in a bond, is high enough, it is more like a transfer and more polar (THINK.)
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Exceptions (to octet)
- Odd # of electrons- rare.
- More than 8 on central atom- only happens w/atoms at least at period 3, because they have d orbitals they can fill
- Less than 8- happens w/ Be and B as central. Technical rule: if formal charge is negative on central or pos on outside, something is wrong; Boron/Be actually more want to lose electrons
Bond enthalpy
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Therefore, total enthalpy of a reaction is (bond enthalpies of bonds in reactants broken) - (bond enthalpies of bonds in products formed.)