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Bonding types w/ electronegativity ranges
- Nonpolar Covalent: 0-<.5
- Polar Covalent: .5-1.7
- Ionic: >1.7
Valence Bond Theory vs. Molecular Orbit Theory
- VBT: Valence bond theory treats every bond as the sharing of electron density between two atoms as a result of the constructive interference of their atomic orbitals
- MOT: uses a mathematical method called the linear combination of atomic orbitals (LCAO) to form molecular orbitals. Each molecular orbital is associated with the entire molecule, rather than just two atoms.
- #atomic orbitals results in # molecular orbitals (antibonding > nonbonding > bonding)
Geometries organized by hybridized orbitals with angle
- sp3: tetrahedral (109.5), trigonal pyramidal, bent
- sp2: trigonal planar (120), bent
- sp: linear (180)
Types of intermolecular forces
- London dispersion
Formal charge on C atoms w/ relation to bonds
Carbon atoms with formal charges will only hold 3 bonds
- Wedge: coming out of page
- Dash: going into page
Resonance Structure rules
- 1. Don't ever break single bonds
- 2. Never exceed an octet for 2nd row elements
Resonance Structure Pattern Recognition
- 1) Allylic lone pair: lone pair next to double bond. Lone pair creates new double bond, old double bond moves to lone pair at end.
- 2) Allylic cation: Cation next to double bond. Double bond moves to positive formal charge, new positive formal charge where double bond is missing.
- 3) Lone Pair Next to cation: Lone pair creates double bond, new positive formal charge formed.
- 4) Double bond between 2 atoms of differing electronegitivity: Double bond moves toward more electronegative atom, creating a negative formal charge, positive formal charge left on other atom.
- 5) Conjugated double bonds in a ring: Each bond moves over.
Ranking of resonance structures
- 1) Minimize the charge (>2 charges is not significant) *Nitro groups chargest aren't associated with that limit
- 2) Electronegative atoms can bear a positive charge ONLY if they have an octet (most significant resonance structures have an octet on all atoms)
- 3) 2 carbon atoms should not have opposite charges
- acid: proton donator
- base: proton acceptor
- Always takes 2 lines
- line 1: from electron on base to H on acid
- line 2: from bond between H on acid and its connected atom
pKa value range
- -10 (very strong acid)
- 50 (very week acid)
Qualitiative acid strength approach
- Look at conjugate base to determine stability
- 1) Which ATOM is the charge on? (more electroneg OR larger)
- 2) Which has more resonance?
- 3) Induction (pulling of e to sigma bond by electroneg atom)
- 4) Orbitals (smaller/rounder = stronger acid)
- EXCEPTION: H-C=C-H + NH2- <-> H-C=-C:- + NH3
- Acetylene is stronger acid!
How does the equilibrium go in an acid/base?
It favors the weaker acid / more stable conj base
How can solvent affect pKa?
Large/bulky bases have less interaction with solute, and are less stable (weaker acid)
- Acid: electron acceptor
- Base: electron donator