Final Exam CHEM 341 Flashcards
Relationship to find formula for Ionic solids
Cation CN/Anion CN =# of anions/# of cations
2 ways to change conductivity
1) Increase Temp (means that more Energy for e- to be promoted)
2) Doping (n-doping (add 1 e-)) and (p doping (1 less e-))
Diodes
Diodes make n/p junctions where Fermi levels line up. This faciitates electron migration into holes.
This movement produces electricity/light
Forward bias
PROMOTES e- and holes combing by negative potential on n-side and positive potential on p side
Reverse bias
PREVENTS e- and holes combing by applying (+) potential to to n side and a (-) potential to the p side
Superconductors def
Conductors of nearly infinate conductance
Superconductors properties
Superconductors work better at low tempertures
More specifically, below Tc or critical temperature
0D defects
Schottky: there is a vacancy in the lattice
Frenkel: the ions are moved to the interstitial site
Factors that change 0D defects
High temp makes Schotttsky more likely because more energy causes atoms/molecules to shift
Frekel more common with small CN
1D defects
Line defects (line of atoms ends prematurely/branches out)
Meisner effect
Superconductors can expel a B field when below Tc
Magnetic moment
mu = root N*(N+2)
Where n is unpaired electrons
MO general rules
of AO=# of MO
Everytime you have a bonding orbital you also have an anti-bonding orbital
Low symmetry groups (3)
C1= no symmetry other than identity
Cs= Only 1 mirror plane and identity
Ci= only an inversion center
High Symmetry groups (5)
Cinfinityv=linear molecules w/o inversion
Dinfinityh= linear molecule w/inversion
Td=tetrahedral with 4 ligands that are identical
Oh=octahedral with identical ligands
In= 120 symmetry elements
Point groups for propeller molecules
Dn=symmetric propeller
Cn=asymmetric propeller
Eclipsed conformation pt group
Dnh
Staggered conformation pt group
Dnd
BCS Theory and why low temp
When e- are in the lattice formation, there are (+) areas around the e- beacause the (+) charges are attracted to the e-
Another e- is attracted to this (+) area and creates cooper pairs. The cooper pairs repulse and switch partners. This interchange is like the electrons moving together. This makes it difficult to impede e- flow
Low temps make it so that the lattice does not vibrate as much and slows e- movement
MO orbitals 3 conditions for bonding
1) Symmetry of the orbitals so that same phase overlaps
2) Atomic orbital energy similar
3) distance between atoms short enough to overlap orbitals not too short that e-/nuclei create repulsion
LCAO steps
1) Find pt group
2)Determine symmetry related fragments of the molecule (ex. bridging, terminal, central atoms)
3) For each fragement, determine the Mulliken labels assoc with AOs of the fragment
a)unmovable atoms
b) sum of characters associated e/relevant atomic orbitals
c) multiply each column for each mulliken symbol
d) REDUCE
e)make matches, matches are bonding and get antibonding
non-bonding left over after bonding
Coordinate system for MO
prinicpal axis of rotation is the z axis
Principal axis of rotation
Axis with the highest n
Degeneracy
how to tell from Char table and Mulliken symbols
2/3 in the first column (identity column) signals and degeneracy
If there is a degeneracy, objects have the same energy level or frequency
The Muliken label E always represents double degeneracy and T represents triple degeneracy
Bond Order
BO=0.5(e- in bonding MO- e- in the antibonding MO)
Ordering d orbitals in MO
On AO side, d orbital most stable for transition metal complexes (lowest in energy)
Predicting IR spectra steps
STEP 1) Draw molecule and assign a coordinate sys
STEP 2) Find pt group + character table
STEP 3) Find reducible rep
3a) uma for each mulliken symbol operation
3b)add up the total x/y/z (ex. z,x,Ry, Rx, and x)
3c) muliply both rows to get reducible rep
STEP 4) reduce (Jacob’s) to determine irriducible rep
STEP 5) Subtract translational and rotational irriducible reps translational (x,y,z) and rotational (Rx, Ry, Rz) to get vibrational modes
STEP 7) Determine if modes are IR or Raman active
IR ACTIVE: has a function of x,y,z
RAMAN ACTIVE: quadratic function of x,y,z
What does reducible rep describe
All possible motions of the molecule
Madelung Constant
M= # of neighbors/distance
Cp ligands are
Weak pi acceptors
How to check for optical isomers
If the structure has no mirror plane-> check optical isomer
If mirror image of structure with no mirror image non-superimposible- optical isomer!
Mixing criteria and results of mixing on energy
Non-bonding and anti/bonding pair of same mulliken symbol (result non-bonding lowered, bonding lowered, anti-bonding raised in energy)
Bonding and Anti-bonding pairs, the more stable pair increases in energy and less stable pair increases in energy
Determining high/low spin for TM complexes (3 factors)
1) 2+ row periodic table- ALWAYS STRONG FIELD= large Deltanaught
2) Ligands via spectrochemical series
top- CO/CN =complex will be strong field
middle- H2O/NH3/en (look @ 3)
bottom-Halgoens/OH- =weak field, small delta naught
or (H(halogens)ONK)
3) Look at the oxidation state of the metal=larger oxidation state= larger deltanaught
Trans effect
Trans influence: The PtiX bond is influenced by the PtiT bond, because both use the Pt px and dx2-y2
orbitals. When the PtiT s bond is strong, it uses a larger contribution of these orbitals and
leaves less for the PtiX bond . As a result, the PtiX bond is weaker, and its
ground state (sigma-bonding orbital) is higher in energy, as in Figure 12.14b . This groundstate, thermodynamic effect is called the trans influence . It contributes to the reaction rate
by lowering the activation barrier for PtiX bond breaking. The ranking below predicts the
order for the trans influence on the basis of the relative s@donor properties of the ligands
trans effect: pi acceptors make metal more positive and weaken bond and so complex wants the incoming ligand more
both stabilize the transition state
