Topic 15 (Part 1) - Principles of Transition Metal Chemistry Flashcards
What is the definition of a d-block element?
An element where the last electron added is in the d - sub shell
How many orbitals are there in a d - sub shell?
5
How many electrons are there in a d - sub shell?
10
What is the definition of a transition metal?
A transition metal is a d - block element which forms one or more stable ions with an incomplete d - subshell
What elements are d - block elements
Sc -> Zn
Why do you normally fill the 4s sub shell before the 3d sub shell?
As the 4s sub shell is at a lower energy level in comparison to the 3d sub shell
When a d-block element becomes an ion which electrons are removed first?
The electrons in the 4s sub shell
Why are the 4s electrons removed first even though they were filled first?
As soon as the 4s sub shell gets filled it acts as the higher energy level sub shell (due to repulsion)
What are the exceptions to the 4s sub shell being filled before the 3d sub shell?
Cr - [Ar] 3d5 4s1
Cu - [Ar] 3d10 4s1
Why are copper and chromium exceptions to the 4s sub shell being filled before the 3d sub shell rule?
They are exceptions because having a full or half filled 3d sub shell is more stable than having a filled 4s sub shell and only partly filled 3d sub shell
Write the electronic configuration for Fe
[Ar] 3d6 4s2
Write the electronic configuration for Cr
[Ar] 3d5 4s1
Write the electronic configuration for Cu
[Ar] 3d10 4s1
Write the electronic configuration for Zn 2+
[Ar] 3d10
Write the electronic configuration for Fe 3+
[Ar] 3d5
Write the electronic configuration for Sc
[Ar] 3d1 4s2
Which 2 d-block elements are not classified as transition metals?
Zinc, Zn, and Scandium, Sc
Why are Sc and Zn not classified as transition metals?
Zn only forms the Zn2+ ion which has a full 3d sub shell, therefore, not a transition metal
Sc only form the Sc3+ ion which has an empty d sub shell, therefore, not a transition metal
What are 5 general properties of transition metals?
- Form complex ions in solutions as ligands join onto the transition metal centre
- They form at least 1 stable ion with an incomplete d-subshell
- They have variable oxidation states
- They are very useful/commonly used as catalysts
- They form coloured compounds
Why do transition metals have variable oxidation states?
- There is not a large energy difference between the 3d and 4s sub shell
- Successive ionisation energies increase gradually until all the 4s and 3d electrons have been removed OR until a stable configuration of electrons is reached
Why is the +2 oxidation state formed by all the transition metals?
This is because all of them can lose 2 electrons form there outer 4s sub shell, as they are the first to go.
Why does Fe form the +2 and +3 oxidation states?
Fe 2+ - formed when 2 electrons are lost from the 4s sub shell
Fe 3+ - formed when 2 electrons are lost from the 4s sub shell and 1 is lost form the 3d sub shell leaving 3d5 which offers the ion stability
Why is the first ionisation energy pretty much the same across all transition metals/ d-block element?
As the first electrons are all removed from the 4s sub shell.
NB: There is a slight increase in first ionisation energy across transition metal elements - this is due to increasing atomic number, therefore, there are more protons in the nucleus (higher nuclear charge) and so stringer forces of attraction between the nucleus and the valence electrons.
However, there is same shielding across all elements as they are all removed form the same shell.
What peaks are there in the second ionisation energy of transition metals?
Chromium and Copper
Why do Cr and Cu have high 2nd ionisation energies in comparison to the other transition metals/ d-block elements?
Chromium - Only had 1 electron in the 4s sub shell and so this second electron is being removed from the 3d orbital going from the stable 3d5 configuration -> 3d4
Copper - Only had 1 electron in the 4s sub shell and so this second electron is being removed from the from the 3d orbital going form the stable 3d10 -> 3d9
Why is the second ionisation energy higher, in general, for all transition metals/d-block elements?
There is a higher proportion of protons to electrons, therefore the electrons are more strongly attracted to the positively charged nucleus - Zn loses this electron quite easily as it goes from 3d10 4s1 -> 3d10 which is a very stable configuration
What is the exception for the third ionisation energy of transition metals/d-block elements?
Fe - As it goes from 3d6 -> 3d5 which is a more stable configuration (no repulsion of electrons as non are in the same orbital)
Why does the transition metal Mn have a high 3rd ionisation energy?
As you are removing the electron that will take it form a stable configuration, 3d5 -> 3d4
Why does the d-block element Zn have a high 3rd ionisation energy?
As you are removing the electron that will take it form a stable configuration, 3d10 -> 3d9
What happens to the d-orbital of the transition metal when it is bonded to a ligand?
When a transition metal bonds to a ligand there is repulsion between the electrons of the ligand and the electrons in the d-orbital of the metal ion - this raises the energy of the d-orbitals. However, due to how the d-orbitals are arranged in space the 5 d-orbitals are split, 2 with a higher energy level and 3 with a lower energy level (an energy gap)
What determines the size of the energy gap between the d-orbitals of the transition metal in a complex ion?
- The nature of the transition metal ion
- its oxidation state
- the nature of the ligands
What happens when white light is passed through a solution of a transition metal complex ion?
Some of the energy from the white light is absorbed to promote an electron from the set of lower energy d-orbitals to the higher set. The remaining wavelengths that are not absorbed are reflected and transmitted into the human eye - the human eye observes the complementary colour of the absorbed wavelengths
Why are the Zn(2+), Cu(+) and Sc(3+) ions colourless when white light is passed through their solutions?
Zn (2+) and Cu (2+) have full 3d sub shells, therefore, no electron can be promoted and so no wavelengths on light are absorbed.
Sc (3+) has no electrons in its 3d sub shell, therefore, no electron can be promoted and so no wavelengths on light are absorbed.
What is the definition of a ligand?
A species that uses a lone pair of electrons to form a dative bond with a metal ion
What is the definition of a complex?
A central metal ion surrounded by ligands - a complex ion has an overall positive or negative charge
What is the definition of the coordination number?
The number of dative/coordinate bonds formed to the central metal ion in a complex
What bonds are formed in complex ions?
dative covalent bonds
Why are dative covalent bonds formed in complex ions?
As ligands have a lone pair of electrons that they can donate to the central metal ion
What 2 factors does the shape of the complex ion depend on?
- The number of ligands formed around the central metal ion
- The size of the ligand
Why do H2O ligands generally form octahedral complexes and Cl- ligands generally form tetrahedral complexes?
Cl - ligands are much bigger than NH3 ligands and Oh- ligands
What are the naming conventions for complex ions?
1 - Number of ligands (di, tetra, hexa)
2 - Name/type of ligand (chloro, aqua, amine)
3 - Name of transition metal ( ending in -ate if the complex ion is negative and spelt normally if the complex ion is positive)
4 - Roman Numerals to show the charge on the metal ion
What do you need to remember when drawing Lewis structures of complex ions?
The bonds are dative, therefore, draw and arrowhead on your bonds from the ligand to the metal
What is the:
- coordination number
- oxidation state of metal
- name of shape
- bond angle
- name of complex ion
of [Cr(NH3)6]3+
COORDINATION NUMBER:
6
OX. STATE OF METAL:
+3
SHAPE:
octahedral
BOND ANGLE:
90
NAME:
hexaaminechromium(III) ions
What is the:
- coordination number
- oxidation state of metal
- name of shape
- bond angle
- name of complex ion
of [CuCl4]2-
COORDINATION NUMBER:
4
OX. STATE OF METAL:
+2
SHAPE:
tetrahedral
BOND ANGLE:
109.5
NAME:
tetrachlorocuprate(II) ions
What is the:
- coordination number
- oxidation state of metal
- name of shape
- bond angle
- name of complex ion
of [Cu(H2O)6]2+
COORDINATION NUMBER:
6
OX. STATE OF METAL:
+2
SHAPE:
octahedral
BOND ANGLE:
90
NAME:
hexaaquacopper(II) ions
State and explain the bond angle of Cl-Cr-Cl in CrCl4-
There are 4 coordinate bonds present in this ion, therefore, the ion has a tetrahedral shape which contains a bond angle of 109.5.
What complexes generally have the tetrahedral structure?
Ones where the ligands are Cl-
What is the:
- coordination number
- oxidation state of metal
- name of shape
- bond angle
- formula
of cisplatin
COORDINATION NUMBER:
4
OX. STATE OF METAL:
+2
SHAPE:
square planar
BOND ANGLE:
90
FORMULA:
[Pt(NH3)2Cl2]
What is cisplatin used as?
An anti cancer drug