Second Test Flashcards
How do you calculate the number of vibrational modes in non-linear compounds?
3N-6 ; N represents the number of atoms in the molecule
What are characters (x)?
tells us whether the irreducible representation is symmetric or antisymmetric with respect to a symmetry operation. (+1 symmetric, -1 antisymmetric)
How are vectors affected after performing a C2 or reflections?
If the origin is moved then all vectors are 0. If it changes direction then is worth -1. If it stays the same it is worth 1.
How is the dimensionality of reducible representations determined ?
Perform symmetry operation on atom, determine if vectors move, sum up the value of the characters representing movement of vectors.
How do you determine the irreducible representation of the motion of a molecule?
Use the reduction formula to reduce the reducible representation into irreducible representation.
a = (1/h) sum(N * Xr * Xi)
h= order : sum of symmetry function coefficients
N = coefficient of symmetry operation
Xr = character of reducible representation (sum of vectors for a particular symmetry operation)
Xi = character of irreducible representation (-1 or +1 based on character table of a point group)
How do you determine the vibrational modes of a molecule from the irreducible representation of all motion of a molecule?
x, y, z - in column 3 represent translational modes
Rz, Rx, Ry - in column 4 represent rotational modes
To obtain irreducible representations for the vibrational modes we subtract out the rotational and translational modes from the irreducible representation of the total motion.
If there are translational modes are present
-A1 -B1 -B2
If there are rotational modes are present
-A2 - B1 -B2
What is remaining is the vibrational modes of the molecule.
How do you predict whether the vibrational modes are IR and/or Raman active?
IR active vibrational modes have x, y, z
Raman active vibrational modes have xy, xz, yz, x^2, z^2 , y^2
How are molecular orbitals created?
They are a combination of the atomic orbitals of the atom. Molecular orbitals are the representation of bonds and show the probable space shared electrons inhabit.
What does sigma mean/pi and asterisk when speaking of molecular orbitals?
Sigma means that is a c2 can be ran through the orbital without changing the position in a noticeable. Pi on the other hand means that when the C2 is ran through the bonding axis the molecular orbital it is distinguishable. An asterisk is denoted when it is an anti bonding orbital.
How can you predict the formation of a molecular orbital?
When the two phases of two atomic orbitals line up?
How do you predict bonding order?
1/2 [bonding-antibonding]
How does the bond order predict the length of the bond?
The lower the bond order the longer the bond.
How does charge affect the length of the bond?
A negative charge will make a bond longer, while a positive charge makes the bond shorter.
How does electronegativity affect the Molecular orbital diagram?
The more electronegative the lower the atom will be on the diagram. That is because the atom can handle more electrons better and is more stable requiring less energy.
How would you describe lewis acids and bases and how would you apply that to ligands?
Lewis acid accept electron density while lewis bases give electron density. The metal would be the lewis acid while the ligands give the electron density.
What makes a lewis base stronger?
The more akyl substituents it posses the more electron density it has to donate.
What is polarizability ?
The degree to which a molecule or ion is distorted by interaction with another molecule or ion.
What are some key trends for hard acids? Soft acids? Hard bases? Soft bases?
Hard acids: alkali metal cations, alkali earth metal cations, early transition metals, transition metals with high positive charges, proton; NOT very polarizable
Soft acids: late transition metals, transition metals with low charges
Hard bases: harder OH2> SH2 > SeH2 softer
harder N»P>As>Sb softer , harder F->Cl->Br->I-
Soft bases: softer I->Br->Cl->F- harder , softer Sb>As>P» N harder
How can the equilibrium constant value reveal the direction a reaction favors?
When the equilibrium constant K>1 the forward reaction is favored (products formation favored)
When K<1 the reverse reaction is favored, formation of reactants favored.
What is a unit cell?
The simplest component of a crystalline solid.
What is a primitive lattice?
A unit cell that has lattice points (represented as spheres) on each vertex
Describe cubic close packing (CCP)
ABC layering, 3rd layer occupies space NOT directly above first layer
Describe hexagonal close packing (HCP)
ABA layering, 3rd layer sits directly above first layer
What is an octahedral hole?
Space resulting from two triangular layers above and below one another.
What is a tetrahedral hole?
Space resulting when trigonal layer is “capped” by sphere in the layer above or below
What is polymorphism ?
A species that can pack into different 3D array based on outside influences such as heat and pressure.
