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
How does cisplatin work?
The 2 chloride ion ligands are displaced and are able to form connections with DNA -> stops the replication of cancerous cells BUT also prevents the replication of healthy cells
In the use of cancer treatment what isomer is used?
Cis, not trans, platin
What is the definition of a monodentate ligand?
Ligands that can only form 1 dative covalent bond with he central metal ion
What is the definition of a bidentate ligand?
Ligands that form two dative covalent bonds with a metal ion
Name two examples of a bidentate ligand
- 1,2 diaminoethane - abbreviated to en
- Ethandioate (C2O4(2-))
Why can 1,2 - diaminoethane act as a bidentate ligand, but NH2NH2 cannot?
The shape that forms when 1,2 diaminoethane bonds to a central metal ion as a bidentate ion is a regular pentagon. Therefore, this allows for the correct bond angle to exist, 109.5
The shape that NH2NH2 forms when it bonds to a central metal ion as a bidentate ligand is an equilateral triangle. This does not allow for the correct bond angle to exist, instead the angle would be 60
What is the hexadentate complex ion you need to know?
EDTA (4-)
What does the hexadentate ligand EDTA4- do to the metal ions that is binds with?
It binds firmly with metal ions, holding them ion solution and making them CHEMICALLY INACTIVE
Why is the H-N-H bond in the ammonia ligand 109.5 and the H-N-H bond in [Cu(NH3)4(H2O)2]2+ 107?
The H-N-H bond in ammonia ligand has 3 bonding pairs and 1 lone pair. Comparatively , the H-N-H bond in Cu(NH3)4(H2O)2]2+ has 4 bonding pairs. Therefore, in Cu(NH3)4(H2O)2]2+ there is equal repulsion between all electron pairs and so a tetrahedral shape is formed. Comparatively, in the ammonia ligand the lone pair-bonding pair repulsion is greater than the bonding pair-bonding pair repulsion therefore the bond angle is smaller
What is the planar ring structure around the Fe (2+) transition metal ion called present in haemoglobin?
porphyrin
What is the name of the iron-porphyrin part of the complex haemoglobin?
The haem group
What happens when you breathe in CO?
CO is a stronger ligand in comparison to H2O, therefore, it bonds to the central Fe (2+) ion more strongly. This is a ligand substitution reaction and it is irreversible which is why less oxygen can be carried around the body.
What is the definition of amphoteric?
A substance that can dissolve in both acidic and alkaline conditions
Which transition metal complex is amphoteric?
Cr3+
Write the equation for the reaction of Chromium (III) with dilute NaOH in solution with state symbols
[Cr(H2O)6]3+ (aq) + 3OH- -> [Cr(H2O)3(OH)3] (s) + 3H2O (l)
What is the observation of the reaction of Chromium with dilute NaOH in solution?
green solution -> pale green precipitate
What is the type of reaction of Chromium with dilute NaOH in solution?
deprotonation
What happens in a deprotonation reaction?
The OH- in NaOH or the NH3 act as bases and accept a proton from the water molecules of the complex ion
Write the equation for the reaction of Chromium (III) with excess dilute NaOH in solution with state symbols
[Cr(H2O)6]3+ (aq) + 6OH- -> [Cr(OH)6]3- (aq) + 6H2O (l)
What is the observation of the reaction of Chromium with excess dilute NaOH in solution?
green solution -> pale green precipitate -> dissolves to deep green solution
What is the type of reaction of Chromium with excess dilute NaOH in solution?
deprotonation
Write the equation for the reaction of cobalt (II) with dilute NaOH in solution with state symbols
[Co(H2O)6]2+ (aq) + 2OH- -> [Co(H2O)4(OH)2] (s) + 2H2O (l)
What is the observation of the reaction of cobalt (II) with dilute NaOH in solution?
pink solution -> blue precipitate
What happens when [Co(H2O)4(OH)2] (s) is left standing?
it changes colour to a pink precipitate
Write the equation for the reaction of cobalt (II) with excess dilute NaOH in solution with state symbols
[Co(H2O)6]2+ (aq) + 2OH- -> [Co(H2O)4(OH)2] (s) + 2H2O (l)
NO FURTHER REACTION OCCURS - the product is insoluble in excess reagant
What is the type of reaction of cobalt (II) with dilute NaOH in solution?
deprotonation
Write the equation for the reaction of iron (II) with dilute NaOH in solution with state symbols
[Fe(H2O)6]2+ (aq) + 2OH- -> [Fe(H2O)4(OH)2] (s) + 2H2O (l)
What is the observation of the reaction of iron (II) with dilute NaOH in solution?
pale green solution -> dirty green precipitate
What is the type of reaction of iron (II) with dilute NaOH in solution?
deprotonation
Write the equation for the reaction of iron (II) with excess dilute NaOH in solution with state symbols
[Fe(H2O)6]2+ (aq) + 2OH- -> [Fe(H2O)4(OH)2] (s) + 2H2O (l)
NO FURTHER REACTION OCCURS - the product is insoluble in excess reagent
What is the type of reaction of iron (II) with dilute NaOH in solution?
deprotonation
What happens when [Fe(H2O)4(OH)2] (s) is left standing?
- The iron oxidises to Fe 3+ on the surface and forms an orange precipitate
- the precipitate darkens
Write the equation for the reaction of iron (III) with dilute NaOH in solution with state symbols
[Fe(H2O)6]3+ (aq) + 3OH- -> [Fe(H2O)3(OH)3] (s) + 3H2O (l)
What is the observation of the reaction of iron (III) with dilute NaOH in solution?
Yellow solution -> orange precipitate
What is the type of reaction of iron (III) with dilute NaOH in solution?
deprotonation
Write the equation for the reaction of iron (III) with excess dilute NaOH in solution with state symbols
[Fe(H2O)6]3+ (aq) + 3OH- -> [Fe(H2O)3(OH)3] (s) + 3H2O (l)
NO FURTHER REACTION OCCURS - the product is insoluble in excess reagent
Write the equation for the reaction of copper (II) with dilute NaOH in solution with state symbols
[Cu(H2O)6]2+ (aq) + 2OH- -> [Cu(H2O)4(OH)2] (s) + 2H2O (l)
What is the observation of the reaction of copper (II) with dilute NaOH in solution?
blue solution -> blue precipitate
What is the type of reaction of copper (II) with dilute NaOH in solution?
deprotonation
Write the equation for the reaction of copper (II) with excess dilute NaOH in solution with state symbols
[Cu(H2O)6]2+ (aq) + 2OH- -> [Cu(H2O)4(OH)2] (s) + 2H2O (l)
NO FURTHER REACTION OCCURS - the product is insoluble in excess reagent
What type of reaction are all the reactions of transition metal complexes with NaOH?
deprotonations
Write the equation for the reaction with state symbols of a small amount of ammonia with Chromium (III) in solution
[Cr(H2O)6]3+ (aq) + 3NH3 (aq) -> [Cr(H2O)3(OH)3] (s) +3NH4+ (aq)
What is the observation for the reaction of a small amount of ammonia with Chromium (III) in solution?
pale green solution -> pale green/grey precipitate
What is the type of reaction of a small amount of ammonia with Chromium (III) in solution?
deprotonation
Write the equation for the reaction of an excess of ammonia/concentrated ammonia with [Cr(H2O)3(OH)3]
[Cr(H2O)3(OH)3] (s) + 6NH3 -> [Cr(NH3)6]3+ (aq) +3H2O (l) + 3OH- (aq)
What is the observation for the reaction of an excess amount of ammonia/concentrated ammonia with [Cr(H2O)3(OH)3]?
green/grey precipitate -> dissolves to purple solution
What is the type of reaction of an excess amount of ammonia/concentrated ammonia with [Cr(H2O)3(OH)3]?
ligand exchange reaction
Write the equation for the reaction with state symbols of a small amount of ammonia with Cobalt (II) in solution
[Co(H2O)6]2+ (aq) + 2NH3 (aq) -> [Co(H2O)4(OH)2] (s) +2NH4+ (aq)
What is the observation for the reaction of a small amount of ammonia with cobalt (II) in solution?
pink solution -> blue precipitate
What is the type of reaction of a small amount of ammonia with cobalt (II) in solution?
deprotonation
Write the equation for the reaction of an excess of ammonia/concentrated ammonia with [Co(H2O)4(OH)2]
[Co(H2O)4(OH)2] (s) -> 6NH3 -> [Co(NH3)]2+ (aq) +4H2O (l) + 2OH- (aq)
What is the observation for the reaction of an excess amount of ammonia/concentrated ammonia with [Co(H2O)4(OH)2]?
blue precipitate -> brown solution
What is the type of reaction of an excess amount of ammonia/concentrated ammonia with [Co(H2O)4(OH)2]?
ligand exchange reaction
Why does darkening of the solution occur in the reaction of ammonia with cobalt (II) in solution?
This is because cobalt (II) is oxidised to cobalt (III)
Write the equation for the reaction with state symbols of a small amount of ammonia with Iron (II) in solution
[Fe(H2O)6]2+ (aq) + 2NH3 (aq) -> [Fe(H2O)4(OH)2] (s) + 2NH4+ (aq)
What is the observation for the reaction of a small amount of ammonia with Iron (II) in solution?
pale green solution -> dirty green precipitate
What is the type of reaction of a small amount of ammonia with Iron (II) in solution?
deprotonation
Which 2 transition metal ions to not dissolve/are involved in ligand exchange reactions in an excess of ammonia?
Fe (II) and Fe (III)
Why does darkening of the solution occur in the reaction of ammonia with Iron (II) in solution?
As Fe (II) is oxidised to Fe(III)
Write the equation for the reaction with state symbols of a small amount of ammonia with Iron (III) in solution
[Fe(H2O)6]3+ (aq) + 3NH3 (aq) -> [Fe(H2O)3(OH)3] (s) + 3NH4+ (aq)
What is the observation for the reaction of a small amount of ammonia with Iron (III) in solution?
yellow solution -> red/brown precipitate
What is the type of reaction of a small amount of ammonia with Iron (III) in solution?
deprotonation
Write the equation for the reaction with state symbols of a small amount of ammonia with copper (II) in solution
[Cu(H2O)6]2+ (aq) + 2NH3 (aq) -> [Cu(H2O)4(OH)2] (s) + 2NH4+ (aq)
What is the observation for the reaction of a small amount of ammonia with copper (II) in solution?
blue solution -> blue precipitate
What is the type of reaction of a small amount of ammonia with copper (II) in solution?
deprotonation
Write the equation for the reaction of an excess of ammonia/concentrated ammonia with [Cu(H2O)4(OH)2]
[Cu(H2O)4(OH)2] (s) + 4NH3 (aq) -> [Cu(NH3)4(H2O)2]2+ (aq) + 2H2O (l) + 2OH- (aq)
What is the observation for the reaction of an excess amount of ammonia/concentrated ammonia with [Cu(H2O)4(OH)2]?
blue precipitate -> dissolves into a deep blue solution
What is the type of reaction of an excess amount of ammonia/concentrated ammonia with [Cu(H2O)4(OH)2]?
ligand exchange reaction
Write the equation for the reaction of the Cl- ligand with [Co(H2O)6]2+
[Co(H2O)6]2+ + 4Cl- <=> [CoCl4]2- + 6H2O
What is the observation in the reaction of the Cl- ligand with [Co(H2O)6]2+
pink solution -> blue solution
What is the type of reaction of the Cl- ligand with [Co(H2O)6]2+
ligand exchange reaction
Write the equation for the reaction of the Cl- ligand with [Cu(H2O)6]2+
[Cu(H2O)6]2+ + 4Cl- <=> [CuCl4]2- + 6H2O
What is the observation in the reaction of the Cl- ligand with [Cu(H2O)6]2+
blue solution -> yellow/green solution
What is the type of reaction of the Cl- ligand with [Cu(H2O)6]2+
ligand exchange reaction
