Topic 15 Flashcards
What are the basic properties of transition metals?
- High density
- Hard solids
- Acts as a catalyst
- All produce coloured compounds and coloured ions
- High Melting and Boiling Points
- Form Ions with different oxidation numbers
- Form ions with incompletely-filled d-orbitals
What elements are in the d-block?
******Some are transition metals******
****Focus on the top row****
What is a transition element?
A transition element is a d-block element that can form at least one stable ion with a partially filled (incomplete) d-subshell
What d-block elements are not transition elements and why?
- Since the d-subshell can only hold 10 electrons
- Scandium and Zinc are not transition metals
- They have completely filled d orbitals
- They do not form a stable ion with a partially d-subshell
- Scandium forms a 3+ ion
How do transition elements lose electrons?
- Loose 4s electrons before 3d electrons
- Making a stable ion
Why can transition metals have varying oxidation states?
- The electron sits in the 4s and 3d energy levels which are very close
- Electrons are gained and lost using a similar amount of energy
What is a complex ion
An ion in which a ******central metal atom (transition element)****** is surrounded by a group of ions or molecules (ligands)
How do you represent a complex ion showing the dative covalent bonds
What is a ligand?
- Any tom, ion or molecule which can donate a pair of electrons to a metal ion (Lewis bases and nucleophiles)
- Classified by the number of dative covalent or coordinate bonds that they can make
- They form single coordinate bonds called unidentate or monodentate (only bonds to the metal once)
- The lone pair of electrons will fill the d-orbital
- Possible due to transition metal ions having a smaller ionic radius which gives rise to a stronger electrostatic field of attraction allowing for ligand formation
What are some examples of ligands
NH3, Cl-, OH-, H2O (All have lone pairs and can form a bond with a transition metal)
How do you name ligands?
Naming Ligands end in O
- Chloro
- Hydroxo
- Aqua
- Amine
What is a Lewis base
A base that donates a proton
Why is water a ligand
- Each molecule makes a single bond with the metal ion
- Where the oxygen which has lone pairs
- Which is attracted to a positive charge
What is a bidentate ligand?
- bidentate ligands contain two atoms that donate pair of electrons to form coordinate bonds
What is the structure of haemoglobin?
What happens when CO bonds to haemoglobin?
What are multidentate ligands?
- Contain more than two atoms that donate pairs of electrons to form coordinate bonds
- EDTA has 6 coordinate bonds
- One EDTA ion per transition metal ion
What happens when the ligands bonds to the metal ion
- The d-subshell is split into 2 when the ligands bond with the central metal ion
- Orbitals gain energy and split into a 2,3 split
- Energy Gap ∆E
What is the energy gap affected by?
The energy gap is affected by:
- Central metal ion as well as the oxidation state
- The type of ligand (monodentate, bidentate, multidentate)
- Coordination number
What happens when light energy is absorbed by electrons in the ground state
- Allows for electrons to absorb light energy from to ground state to an excited state
- This requires the energy inputted to be equal to the energy gap
What happens to the frequency of the energy absorbed?
- Some frequencies absorbed are of the visible light spectrum
- Which is dependent on the frequencies absorbed by the size of the energy gap
In terms of the colour spectrum where does the energy gap frequency lie?
- Red is the lowest frequency
- The higher the energy gap the further along the spectrum the colour would be
- Blue is the highest frequency
How is the colour shown in transition metals?
- Frequencies that aren’t absorbed are reflected or transmitted
- Meaning the rest of the unabsorbed colour forms a complementary colour
- Example - Frequency for light blue is absorbed meaning the complementary colour red is produced
Why is a colour not shown in some d-block elements?
HOWEVER, complexes that have a full 3d or lack a 3d subs-shell with no electrons can migrate to a higher energy level meaning there is no colour produced
What is the coordinate number?
The number of different coordinate bonds to the metal ion
Why are H20, OH- and NH3 monodentate ligands?
They all have lone pairs which can form a dative covalent bond with a metal ion
What is the shape when and name when there is a complex with a coordinate number of 6?
- Monodentate Ion
- Octahedral Shape
What is the name of a complex with different ligands attached to it?
Why do complexes with Cl- form a different shape?
What are the different shapes in comparison to the number of ligands and the bond angles for each?
What is Cis-platin and its properties
What are trans-platin and its properties?
What shape do both trans and cis-platin have?
Why is it important to filter which version of platin you get?
- When you form platin a racemic mixture is formed
- So there is an even amount of cis and trans
- Meaning that its unknown whether the trans would be more toxic and outweigh the benefits of cis if you were to give to a patient and vice versa
- That’s why you have to use plane polarised light to filter the trans from the cis
What is the different ions of vanadium?
What happens when you reduce vanadium from +5 to +2
- Use ammonium vanadate(V)
- In acidic solution the compound has VO2+
- With zinc catalyst the ion reduces
- Causing a change of yellow to blue to green
**VO2+ , VO 2+, V 3+**
Why is a reduction of vanadium 5+ to 4+ feasible?
- Electrode potential of the reduction reaction (first one) is more positive than the oxidation reaction is negative
- E0cell=E0red−E0oxid
- Zn is electron releasing with respect to VO2+
Why is a reduction of vanadium +4 to +3 feasible
- Electrode potential of the reduction reaction (first one) is more positive than the oxidation reaction is negative
- E0cell=E0red−E0oxid
- Zn is electron releasing with respect to VO +2
Why is a reduction of vanadium 3+ to 2+ feasible?
- Electrode potential of the reduction reaction (first one) is more positive than the oxidation reaction is negative
- E0cell=E0red−E0oxid
- Zn is electron releasing with respect to V 3+
Why is the reduction of +2 to 0 not feasible
- Electrode potential of the reduction reaction (first one) is less positive than the oxidation reaction is negative
- E0cell=E0red−E0oxid
- Zn is electron releasing with respect to V 2+vv
What are the different variable oxidation states?
How can Cr2O7 2- be reduced to 2Cr 3+?
- Colour change from orange to green
- Zinc is used as catalyst
- Positive electrode potential because of voltage
How can you reduce Cr3+ ions to Cr2+?
- Zinc acts as a catalyst and increases in oxidation number because of an increase in oxidation number
- Chromium is reduced with a decrease in oxidation number
- Cr2+ I unstable and is readily oxidized back into Cr3+ from oxygen in air
- Just feasible but not over +0.6V
- Blue to green
How are chromium ions oxidised?
- Cr3+ ions oxsidised using hydrogen peroxide in alkaline slution
- As pH can change the amount of CrO4 2-
- Green to yellow
- Chromate ions exist in equilibrium with dichromate
How is pH related to dichromate and chromate resersable reaction
- oxidation states don’t change → equilibrium
- In acidic conditions you will have dichromate
- In alkali conditions you will have chromate
What is the general reaction of transition metals with sodium hydroxide or ammonia solution?
- There would be proton transfer between the transition metal and ammonia solution/sodium hydroxide
- Which then forms a precipitate which is coloured
What happens when you add excess sodium hydroxide solution?
- Proton Transfer between precipitate and sodium hydroxide
- Precipitate dissolves
What happens when excess ammonia is added?
- Ligand exchange happens between ligands on complex and ammonia
- Precipitate dissolves
What is the reaction table for the transition metals?
What are the reactions of chromium in aqueous sodium hydroxide and aqueous ammonia?
What are the reactions of manganese in aqueous sodium hydroxide and aqueous ammonia?
What are the reactions of iron(II) in aqueous sodium hydroxide and aqueous ammonia?
What are the reactions of iron(III) in aqueous sodium hydroxide and aqueous ammonia?
What are the reactions of Nickle in aqueous sodium hydroxide and aqueous ammonia?
What are the reactions of Copper in aqueous sodium hydroxide and aqueous ammonia?
What are heterogeneous catalysts?
- One that is a different phase from the reactants
**Like breaking down hydrogen peroxide (liquid) with manganese oxide (solid)**
Why are transition metals good heterogeneous catalysts?
- Good solid catalyst
- Change oxidation number by gaining or losing electrons in the d-orbital
- Allowing for the transfer of electrons to speed up reactions
- Reactions only happen on the surface
- This is why we use powder rather than large lumps
- Also why it’s used to coat an inert supporting material
What is the step in the surface adsorption theory?
- Adsorption - 1+ reactants attach to the surface of the catalyst
- Reaction - Bonds are tweaked in the adsorbed reactants
- Desorption - Product becomes detached from the surface of the catalyst
What are the steps in the contact process?
Why are Carbon Monoxide and Nitrogen Monoxide bad?
- Carbon monoxide interferes with oxygen transport around the body
- Nitrogen monoxide is easily oxidised to nitrogen dioxide which forms acid rain
- Both formed through the incomplete combustion of hydrocarbon file
How does the catalytic converter convert these gases?
What are homogenous catalysts?
- A catalyst that is in the same phase as the reactants
- All gases or all in an aqueous solution
- Less common in industry
- Forms an intermediate species for which a specific formular can be written
What is the reaction with persulfate ion and what are the problems?
What are the steps in the reaction with persulfate using Fe2+
What is the steps in the reaction with persulfate using Fe3+?
What is the steps in the reaction with persulfate using Fe3+?
What elements beside transition elements can form metal ion complexes
Zinc and Aluminum
