Topic 15 - Transition Metals Flashcards
Where in the periodic table are transition metals found?
d - block
What is a transition metal?
d - block elements that form one or more stable ions with incompletely filled d-orbitals
Between what elements are d-block elements?
Sc to Zn
Between what elements are transition metals?
Ti to Cu
Why aren’t Sc and Zn transition metals?
Their ions do not form incomplete d-orbitals
What are the characteristics of transition metals?
Hard solids.
High melting and boiling temperatures.
Can act as a catalyst.
Form coloured ions and compounds.
Form ions with variable oxidation states.
What is the d-orbital?
A double dumbbell shape made of 5 orbitals.
What are the exceptions to the normal filling order?
Chromium and Copper - they only have 1 electron in the 4s shell.
How can electronic configurations be abreviated?
By using the EC of Ar.
e.g. titanium would be [Ar] 4s2 3d2
What is the electronic configuration of Ar?
1s2 2s2 2p6 3s2 3p6
How many electrons are there in [Ar]?
18
What is a ligand?
A molecule or ion that donates a pair of electrons to the central metal ion to make a dative covalent bond.
What is a complex ion?
A transition metal with a ligand attached by a dative covalent bond.
What is a monodentate ligand?
A molecule/ion that has one atom that donates a pair of electrons to the central metal ion in a dative covalent bond.
What is an example of a monodentate ligand?
H2O
What is the co-ordination number for a monodentate ligannd?
6
How does H2O act as a ligand?
The O donates a pair of electrons for a dative covelant bond. 6 water molecules are needed for a full hydration. e.g. [Cu(H2O)6]2+
What is a bidentate ligand?
A molecule/ion that has two atoms that donate a pair of electrons to the central metal Ion in a dative covalent bond.
What are examples of bidentate ligands?
Diaminoethane (en)
H2N: - CH2 - CH2 - :NH2
or Ethane Dioate ions
-O - C=O - C=O - O-
What is the co-ordination number of a bidentate ligand?
3.
as each molecule has two places that can donate a pair of electrons to the CMI.
How does diaminoethane (en) attach to a CMI?
The nitrogen’s donate their lone pair of electrons to the CMI. As there are two nitrogens in the molecule there are two dative covalent bonds made per molecule.
[Cu(en)3]+2
How do ethane dioate ions attach to the CMI?
The oxygens (O- not =O) donate their lone pair of electrons to the CMI. As there are two oxygens in the molecule there are two dative covalent bonds made per molecule.
[Cu(C2O4)3]-4
What is a multidentate ligand?
A molecule/ion that has more than two atoms that can donate a pair of electrons to a central metal ion in a dative covalent bond.
What is an example of a multidentate ligand?
EDTA-4
(Ethylenediaminetetraacetic acid)
What is the structure of EDTA-4?
. O O
|| ||
-O - C - CH2 C - O-
| |
N: - CH2 - CH2 - N:
| |
-O - C CH2 - C - O-
|| ||
O O
What are complimentary colours?
Colours opposite each other on the colour wheel.
Why do we see the complementary colour with transition metal complexes?
Light energy is adsorbed by the compound meaning that there will be a greater proportion of the complementary colour reflected - which we see as the complementary colour to the object.
What causes the colour of a transition metal complex?
The ligand approches the transition metal ion and electron-electron repulsion causes the d-orbital to split.
When white light is shon on the complex certain wavelengths/frequencies of light are absorbed to move electrons from a lower energy level to a higher one (promotion/excition).
The amount of energy absorbed depends on the differance in energy between the two levels.
The wavelength of light reflected depicts the colour seen.
What happens to the electron after if gets promoted in a TMC?
The electron doesn’t come back down
What is the relationship between the movement of the electron and the colour seen for the TMC?
The amount of energy gained by an electron is directly proportional to the frequency of light absorbed. This is inversely proportional to the frequency transmitted.
What effects the energy gap of the TMI?
The charge of the TMI, the number of ligands attached and the type of ligand.
What is the shape of a molecule with 6 ligands?
Octahedral
What is the shape of a molecule with 4 ligands?
Tetrahedral
What is the shape of a molecule with 2 ligands?
Linear
What is the co-ordination number of an octahedral molecule?
6
What is the bond angle of an octahedral molecule?
90°
What is the coordination number of a linear molecule?
2
What is the bond angle of a linear molecule?
180°
What is the frequent example of a linear TMC?
Tollens reagent [Ag(NH3)2]+
What is the coordination number for a tetrahedral molecule?
4
What is the coordination number for a square planer molecule?
4
When will a molecule be tetrahedral and when square planer?
Only platinum forms square planer TMCs.
What is an example of a tetrahedral TMC?
[CuCl4]-²
What is an example of a square planer TMC?
[Pt (NH3)2 (Cl2)2]
What stereoisomerism is present in linear complexes?
No stereoisomerism
What stereoisomerism is present in tetrahedral complexes?
Optical isomerism
What stereoisomerism is present in square planer complexes?
Cis/trans isomerism
What stereoisomerism is present in octahedral complexes?
Both optical and cis/trans isomerism
How is optical isomerism shown in tetrahedral complexes?
The transition metal acts as the chiral part with 4 different ligands attached.
What is an example of an optical isomer in a tetrahedral complex?
[Co I Br Cl NH3]-¹
NH3 | NH3
| | |
I - Co ░ Cl | Cl ░ Co - I
▼ | ▼
Br | Br
When is the TMC a cis isomer?
When the same ligands are next to each other
When is the TMC a trans isomer?
When the same ligands are opposite each other.
Cis and trans isomer
do diagram
What is a catalyst?
A chemical that speeds up the rate of reaction without being chemically changed during the process. It provides an alternative pathway for the reaction with a lower activation energy.
What are the types of catalyst?
Heterogenous and homogenous
What is a hetrogenouse catalyst?
A catalyst that is in a different state/phase to the reactants.
What are the 3 parts of the surface adsorption theory?
Adsorption.
Reaction.
Desorption.
What happens in the adsorption phase of the surface adsorption theory?
One or more reactants become attached (adsorbed) to the surface of the catalyst.
What happen in the reaction stage of the surface adsorbtion theory?
Weakening of the bonds in the reactants leading to the formation of the products.
What happens in the desorption phase of the surface adsorption theory?
The product detaches from the surface of the catalyst.
How does vanadium pentoxide (V2O5) act as a catalyst?
By changing oxidation state
How does vanadium pentoxide act as a catalyst in the oxidation of SO2?
SO2 + O2 → V2O4 + SO3
V2O4 + ½O2→ V2O5
What is a homogenous catalyst?
A catalyst that is in the same state/phase as the reactants
What does the presence of a homogenous catalyst cause?
An intermediate species
How does iron catalyse the reaction of S2O8²- with I-?
S2O8²- + 2Fe2+ → 2SO4²-
+ 2Fe³+
2Fe³+ + 2I- → 2Fe²+ + I2
All in an aqueous state
Why does iron act as a catalyst in the reaction of S2O8²- with I-?
Both S2O8²- and I- are negatively charged so repel each other. Fe2+ ions are not repelled by S2O8²- as they have an opposite charge so they react. This forms Fe³+ ions that can react with I- ions to form I2 and reform Fe²+
What does cis platin consist of?
A central platinum ion with two chloride (Cl-) ligands and two ammonia (NH3) ligands attached. The lone pairs of the ligands form dative covalent bonds with the central platin.
What does cis platin act as?
An anti-cancer drug
How does cis platin bond with DNA?
Ligand substitution takes place and the chloride ligands are substituted with water molecules. The water is then substituted by a hydrogen atom in guanine. Dative covenant bonds form between the lone pair on hydrogen and the central platinum ion. Makes two dative covelant bonds.
How does cis platin have anti-cancer qualities?
It stops uncontrolled cell division and DNA replication
Why cant trans platin act as an anti cancer drug?
The second Cl-/H2O is too far away from the other so it cant form two dative bonds. Only one.
What is the function of haemoglobin?
Transport oxygen around the body in the blood
What is the structure of haemoglobin?
A globin protein with 4 haem groups around it. The haem group consists of a central iron(2+) and 4 N atoms.
How does the haem group transport oxygen?
Oxygen acts like a ligand, using its lone pair to form a temporary dative bond with Fe2+
How does Carbon monoxide attach to the haem group?
CO has a lone pair of electrons on the C that allows it to act as a ligand, forming a dative covalent bond.
How does the strength of the bonds between CO and haem and O and haem vary?
The strength of the covalent bond between oxygen and haemoglobin isn’t very strong so it can allow oxygen to be dropped off where needed.
CO is a stronger ligand and stronger covalent bonds are formed with haemoglobin than O2. CO bonds irreversibly to the haem group.
What does the varying strength of bonds to the haem group mean?
CO will bond to haemoglobin before O2 and will replace any O2 that is already bonded as CO has a higher affinity.
Why is CO poisoning a problem?
As CO bonds irreversibly to the haem group instead of Oxygen it means that oxygen cant be transported to cells and they end up dying which causes harm to the person and could lead to death.
What are the types of reaction that a transition metal can undego?
Redox.
Acid-Base.
Ligand Substitution.
Change in co-ordination number.
What happens in a redox transition metal reaction?
Change in the oxidation number.
What doesn’t change in a redox transition metal reaction?
The type and number of ligands
What is an example of a redox transition metal reaction?
Oxidation, in air, of Fe2+ to Fe3+
What is the equation for the oxidation of Fe2+ complexes?
[Fe(H2O)6]2+ →(in air)→ [Fe(H2O)6]3+
What happens in Acid-Base transition metal complex reactions?
The base removes hydrogen from the ligands.
What effects the number of bases needed for an Acid-Base transition metal reaction?
The charge of the complex ion
What is an example of an Acid-Base reaction with a copper complex?
[Cu(H2O)6]+2 + 2OH- → [Cu(H2O)4(OH)2] + 2H2O
How can the copper complex Acid-Base reaction be reverced?
By using HCl. Reforms [Cu(H2O)6]2+
What is an example of a ligand substitution reaction with a copper complex?
Reaction with excess NH3
How does ligand substitution take place with excess NH3?
Two OH- and two H2O get substituted by NH3:
[Cu(H2O)4(OH)2)] + 4NH3 → [Cu(NH3)4(H2O)2)] + 2H2O + 2OH-
What happens in a reaction with a change in coordination number?
Involves a change of ligand
What is an example of a reaction that has a change in coordination number?
Copper complex reacting with concentrated HCl:
[Cu(H2O)6]+2 +4Cl- ↔ [CuCl4]-2 + 6H2O
Why does the coordination number change for reactions with concentrated HCl?
Cl- is a larger ligand than H2O so the central metal ion can only accommodate 4 Cl- ligands to keep electron-electron repulsion to a minimum.
What reactions can Iron(II) and Iron(III) complexes undergo?
Redox and acid base only
What is the Iron(II) complex?
[Fe(H2O)6]2+
How does the iron(II) complex react with NaOH?
[Fe(H2O)6]+2 + 2OH- → [Fe(H2O)4(OH)2] + 2H2O
What colour is [Fe(H2O)6]2+?
Pale green solution
What colour is [Fe(H2O)4(OH)2]?
Green Solid
How does the Iron(II) complex react with NH3?
[Fe(H2O)6]+2 + 2NH3 → [Fe(H2O)4(OH)2] + 2NH4^+
How can the reactions of Iron(II) complexes with alkalis be reversed?
By using HCl
What happens to the [Fe(H2O)4(OH)2] formed if left in air?
Gets oxidised to form [Fe(H2O)3(OH)3]
What colour is [Fe(H2O)3(OH)3]?
Brown solid
What is the Iron(III) complex?
[Fe(H2O)6]3+
What colour is [Fe(H2O)6]3+?
Yellow/brown solution
How does [Fe(H2O)6]3+ react with NaOH?
[Fe(H2O)6]+3 + 3OH- → [Fe(H2O)3(OH)3] + 3H2O
How does [Fe(H2O)6]3+ react with NH3?
[Fe(H2O)6]+3 + 3NH3 → [Fe(H2O)3(OH)3] + 3NH4^+
What is the cobalt complex?
[Co(H2O)6]+2
