Test 2 Flashcards
How do I find the point group of a crystal?
Drop uppercase letter. Take the lower case letters of the space group and change all of them to “m”s
What is a crystal system?
It is the shape of the crystal. Examples: triclinic, tetragonal, hexagonal, cubic, monoclinic
What is a space group?
It is a description of the symmetry of a crystal. Will be given.
What is Fidel’s law?
It states that every crystal diffraction has inversion symmetry but that does not mean that a molecule has inversion symmetry too which causes problems
What is diffraction symmetry? What is it known as? How do I find it?
It is also known also Laue symmetry. It is the bold point group at the bottom of a single box
What coordinations number is the most common in transition metals? What else can it be? When is it each? Exception?
6=octehedral Tetrahedral or square planar Something is square planar if it has both d8 electrons and on 2nd or 3rd row. Ni can be both
What are the isomers for a coordination number of 4?
If square planar, it can have cis or trans isomers (cannot be chiral b/c mirror planes) If tetrahedral you can have chiral molecules if all groups are different.
What are the geometries for a coordination number of 5?
We can have trigonal bipyramidal (small groups on axial) Or square pyramidal. All of the groups part of the square are the same
What are the isomers we learned for metals with a coordination number of 6?
If 2 groups are the same it can be cis or trans If 3 groups are the same, it can be a meridinal isomer (mer-) or facial (fac-)
What is an example of linkage isomerism?
an ambi-dentate molecule that can bind to a ligand at more than one place
What do n and muo notation tell me?
both tell how many ligands are attached to the metal(s)
What is the chelate effect?
A chelate is a polydentate ligand. It refers to the fact that chelating ligands are often preferred because they add increases stability. It is favored by entropy. Since it is more stable, chelating ligand is harder to take off.
What is one reason why it is more difficult to detach a chelating ligand?
It is more difficult to detach because if only atom of ligand gets un-bonded, it does not go far away and it can reattach. Also, there is less of a chance that all bonds formed by a chelate will breaks at the same time to allow ligand to float way
What is braggs law? Implications?
Braggs law will tell us the path difference between two diffracted waves. We can also calculate the incident angle. The law is: 2dsin(theta)= integer(wavelength) If n is an integer, means waves will constructively interfere to produce a large peak.
How do i find the lattice symmetry?
It is the bottom bolded point group for the crystal system a space group is found in
How do I find laue symmetry?
It is the bolded point group at the bottom of a single box
What is meant by centrosymmetric? How do i know if it is centrosymmetric?
It has inversion within molecule. If it is in a laue group, it has inversion
What is meant by a crystal being enatiomeric? How do i know if a crystal is enantiomeric?
It means that one enantiomer can crystalize by itself. If space group has only a rotational axis- this incudes point groups that only have plain numbers(top of a box)
What is a Coordination #?
Number of ligands a metal can attach to
what do mono-, bi-, tri-, and poly-dentate refer to? Ambi-?
The number of places of attachments a ligand can make. Ambi means there is more than one donor atom.
What is a chelate?
a ligand that can form a ring to include metal.
What is ionization isomerism?
It is when a ligand and a counter ion exchange places
what is hydrate isomerism?
It is when a ligand and a counter ion exchange places except this time the ligand is water
What is coordination isomerism?
Occurs when we have a complex molecule and it can rearrange as long as it keeps the same molecular formula.
What is geometric isomerism?
isomer of a compound that involves the change in geometry ex) tetrahedral and square planar
What is the mechanism for Berry pseudo-rotation?
It refers to the distortion of a trigonal bipyramid to a square pyramid and back to trigonal bipyramidal
How do I find d electron count?
find oxidation state and subtract from number of electrons
What can I say about early transition metals? (5)
- Larger because less e-. This means they can accommodate more ligands 2. They are electropositive to they bind well to OXYGEN and halogens 3. They make hard, heat resistant materials with e.n. elements 4. Readily make double or triple bonds with O, N, and C 5. Make metal-metal multiple bonds, esp 2-3rd rows
What can I say about the late transition metals? (Ni and up)
- Are more electronegative so the bond better with anionic or neutral ligands. Means more covalent character. Bond well to SULFUR and nitrogen 2. Like to form metal-metal single bonds. Esp 2-3rd rows 3. For. Tetrahedral, square planar or octahedral compounds 4. Are smaller
What can I say about the borderline transition metals?
- act like both early or late transition metals 2. Binds well to NITROGEN and sulfur and oxygen
What are normal oxidation numbers for the first row?
To the left of Mn we start to increase up to +4, to the right including Mn all are 2+
What type of field do 1st row trans. metals form?
Weak.
What are normal oxidation numbers for the 2nd and 3rd rows of the trans. metals?
Early trans. metals have max valance oxidation #s. O.N. decrease across
What type of field do 2nd and 3rd row trans. metals make?
strong field.
What can we say about bond strength of 2nd and 3rd row trans. metals?
they form stronger metal-metal and metal-ligand bonds
What is special about the electronegativity’s going from the 1st row to the 2nd and 3rd row trans. metals?
as we go down, electronegativity increases `
In a Pourbaix diagram, when do I know when a species is oxidizing or reducing?
Species above water line are oxidizing agents (oxidizes water), below are reducing agents (reduces water)
What is being measured in a Pourbaix diagram?
reduction potential. If high positive number it is likely to be reduced and be an oxidizing agent
What do dotted and solid lines mean in a Pourbaix diagram? Slanted line?
Dotted=both in solution or water stability lines; solid= one is in enclosed is a solid. Slanted line means that pH affects reduction potential
What are trends for CN?
First row can make all kinds of CN. 2nd and 3rd row are usualky form octahedral or square planar. Early metals form mostly octahedral while late trans metals vary
