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- Kf1 (general formulas) Kf2
- M + L --> M-L ML + L --> ML2
- general stepwise formation constants
- ML(n-1) + L --> M-L(n)
- the value of Kf represents
- the strength of binding of the ligand relative to H2O.
- labile
- undergoes rapid equilibration (ex. ligands pop on and off)
- inert
- complex has longevity (ex. rocks)
- formation constant
- expresses the strength of a ligand relative to the strength of the solvent molecules (usually H20) as a ligand.
- Stepwise formation constant
- the formation constant for each individual solvent replacement in the synthesis of the complex.
- 4 common types of lewis acids:
- 1) molecule with incomplete octed that can accept a lone pair (ex. B(CH3)3 can accept lone pair of NH3 2) metal cation can accept an electron pair (ex. Co2+) 3)A molecule or ion can rearrange if it has a complete octet to accept an electron pair (ex. CO2) 4) A molecule may be able to expand its valence shell to more than 8. (ex. SiX4, AsX3, PX5)
- superacids
- substances that are more efficient proton donors than 100 mass % H2SO4. Formed when powerful lewis acid is dissolved in powerful bronsted acid. (Common one is formed when SbF5 is dissolved in HSO3F or HF) Others that can be combined with these 2: AsF5, TaF5, NbF5, PF5
- Halogens that are lewis acids
- Br2 and I2
- Complex Formation
- most simple acid base reaction. A + :B --> A-B.
- Displacement Reaction
- Acid base reaction. An acid or base drives out another acid or base from a lewis complex. B-A + B:' --> B: + A-B OR A' +B-A --> A'-B +A. Also called a substitution reaction
- Metathesis reactions
- Displacement reaction assisted by the formation of another complex. AKA double displacement reaction. A-B + A'-B' --> A-B' +A'-B
- Hard acid-base interactions are:
- predominantly electrostatic (ionic interactions)
- Soft acid-base interactions are:
- predominantly covalent.
- Most solvents are:
- either electron pair acceptors or donors (lewis acids or bases)
- common basic solvents:
- water, alcohols, ethers, amines, DMSO (dimethylsulfoxide), DMF, acetonitrile (all are polar solvents and hard lewis bases)
- common acidic solvents:
- sulfur dioxide is a good soft acidic solvent for dissolving soft bases such as benzene.
- hard acids (4)
- small ionic radius, high positive charge, no electron pairs in valence shell - likely to be strongly solvated b/c water is a base!
- soft acids (3)
- large radius, low (+) charge, electron pairs in balence shells
- hard bases (1)
- small,EN atomic centers
- soft bases (1)
- large atoms of intermediate EN
- elements that form strongly acidic compounds:
- everything in the p-block right of and including : B, Si, Se, and Te. Also if these have oxidation states of 5+ : As, Sb, and Bi (anything lower and they are amphoteric!!)
- elements that form strongly basic compounds:
- All of s block except Be and including Tl of p-block.
- elements that form amphoteric compounds:
- Anything in between acids and bases line and including As, Sb, and Bi if ox state is lower than 5.
- to calculate the concentration of final product we use:
- overall formation constant: M + n*L --> ML(n) Bn = K1*K2*K3....
- Inverse of Kf is:
- dissociation constant K(d) = 1/K(f)
- chelate effect
- the greater stability of a complex containing a coordinated polydentate ligand compared with a complex containing the equivalent number of analogous monodentate ligands; it is largely an entropic effect.
- dissociative mechanism
- a reaction sequence in which an intermediate of reduced coordination number is formed by the departure of the LG. (LG leaves at same time new ligand attaches) Cant isolate transition state but can isolate an intermediate.
- associative mechanism
- involves a step in which an intermediate is formed with a high coordination number than orig. complex.
- interchange mechanism
- takes place in one step. No intermediate is formed.
- trans effect
- the effect of a coordinated ligand upon the rate of substitution of ligands opposite to it.
- steric crowding does what
- inhibits associative reaction and facilitates dissociative.