Transition Metals Flashcards
Where are the transition metals on the periodic table?
They are directly under and include the row between titanium to copper.
Physical properties of elements from titanium to copper.
Good conductors of heat and electricity. Hard, strong, shiny and have high melting and boiling points.
Which orbital are the first electrons gained or lost from for the first row of transition metals?
4s
Define a transition element
An element that forms at least one stable ion with a part full d-shell of electrons.
Chemical properties of transition metals
They have variable oxidation states. They form coloured ions. They or their compounds can show catalytic activity. They form complex ions.
What is a complex ion?
A transition metal surrounded by ions or other molecules (collectively ligands) which are bonded to it by co-ordinate bonds.
What is a ligand?
An atom, ion or molecule that forms a co-ordinate bond with a transition metal ion using a lone pair of electrons.
What is the co-ordination number?
The number of co-ordinate bonds to ligands that surround the d-block metal ion.
Shapes and examples for co-ordination numbers 2,4,6
2: linear. Example Ag+ complexes
4: tetrahedral (more common). Example large ligands like Cl-
4: square planar (less common). Example Pt2+ or Ni2+ complexes
6: octahedral. Most common out of all transition metals.
What is a Lewis acid?
An electron pair acceptor.
What is a Lewis base?
An electron pair donor.
What are aqua ions and how do they form?
If you dissolve the salt of a transition metal in water, the positively charged metal ion becomes surrounded by water molecules acting as ligands. Normally there are 6 water molecules in an octahedral arrangement. The resulting species are called aqua ions.
What is a multidentate ligand?
A ligand that has more than one atom with a lone pair of electrons which can bond to a transition metal ion.
Which ligand is often abbreviated to en?
Ethane-1,2-diamine
How many do-ordinate bonds can EDTA have and what is its charge?
6 bonds
4-
What are chelates?
Complex ions with polydentate ligands
What is the chelate effect?
Where chelate complexes with polydentate ligands are favoured over complexes with monodentate ligands. There is an increase in entropy and the change in enthalpy is negligible as the same number of the same type of similar bonds are being broken and formed.
What is chelation?
The process by which a multidentate ligand replaces a monodentate ligand in forming co-ordinate bonds to a transition metal ion
How to draw complex ions
Put metal in middle. Draw 3D bond shape. Add ligands. Draw square brackets around whole molecule. Put charge in top right, X+.
Describe cis-trans (geometrical) isomerism in complexes
A special type of E-Z isomerism. Occurs in octahedral or square planar complexes when there are two types of ligand. The ligands of the same type could be next to each other (cis) or on opposite sides of the central metal ion (trans).
Describe optical isomerism in complexes
Happens when there are 2 or more bidentate ligands is an octahedral complex. The two optical isomers are mirror images of each other and rotating either one cannot make the ligands all go in the same positions as the other.
Why are transition metal complexes coloured?
The transition metals have part filled d orbitals. It’s therefore possible for electrons to move from one d orbital to another. In a compound, the presence of other atoms nearby makes the d orbitals have slightly different energies. Electrons move from one d orbital (in ground state) to another of a higher energy level (excited state) if they absorb energy equal to the difference in energy between levels. This energy is often in the visible part of the EM spectrum. This colour is therefore missing from the spectrum and you see a combination of the colours not absorbed.
What affects the colour of transition metal complexes?
The energy gap between d orbitals. This is affected by the oxidation state of the metal, the type of ligands and the shape of the complex ion.
Colour and formula of Vanadium in oxidation states +5 to +2
\+5 is VO2 +, yellow \+4 is VO 2+, blue \+3 is V 3+, green \+2 is V 2+ violet All aqueous. You Better Get Vanadium
Conditions for reducing vanadium
Zinc is reducing agent. In acidic conditions (hydrochloric or sulfuric). No air in which would prevent V(+2) forming.
How does colorimetry work?
A colorimeter uses a light source and detector to measure the amount of light of a particular wavelength that passes through a coloured solution. The more concentrated the solution, the less light is transmitted through the solution (higher absorbance). You can use a calibration graph of absorbance or transmittane against concentration to find the unknown concentration of a coloured solution.
How does pH affect how easily a transition metal is oxidised or reduced?
Easier to oxidise transition metal in alkaline conditions. Easier to reduce transition metal is acidic conditions.
Conditions for MnO4- to work as oxidising agent and explain
Used in acidic conditions and dilute sulfuric acid is the acid used. Can’t use HCl as the MnO4- would also oxidise Cl- to Cl2 affecting the volume of MnO4- required. Can’t use concentrated sulfuric or nitric acid as these are oxidising agents as well so affect volume of MnO4- required. Can’t use a weak acid as wouldn’t provide enough H+ ions.
Half equation for MnO4- ions acting as oxidising agent
MnO4- + 5e- +8H+ -> Mn2+ + 4H2O
Which iron ion is analysed using potassium manganate?
Fe2+
Half equation for oxidation of ethanedioate ions
C2O4 2- -> 2CO2 + 2e-
Ratio of ethanedioate ions to manganate ions in redox titration
2.5:1
What are heterogenous catalysts and how do they work?
Catalysts that are present in a reaction in a different phase to the reactants. Their catalytic action occurs on the active sites of the solid surface and the reactants pass over the surface. At least one reactant is adsorbed onto the surface. This weakens bond within the reactant and holds reactants closer together in the correct orientation to react.
How to make catalysts more efficient
Increase surface area as reactions only take place on surface. Spread catalyst onto inert support medium to increase surface to mass ratio.
Describe poisoning.
Happens in heterogeneous catalysts. Unwanted substances adsorb strongly to the surface and blocks the active sites.
What is a homogenous catalyst?
A catalyst that is in the same phase as the reactants.
How do homogenous catalysts work?
The transition metal can vary oxidation states to either give or receive electrons to reactants. This is especially helpful for reactions involving species of the same type of charge. The reaction proceeds through an intermediate species.
What is autocatalysis?
Where one of the products of a reaction is a catalyst for the reaction.
Rate of reaction curve for autocatalysis reactions
Concentration of reactants against time. Starts slow at uncatalysed rate. Then reaction speeds up to catalysed rate. From then on behaves like a normal reaction. Bit like cos graph from 0 to 180.
Ratio of Fe2+ to MnO4- ions in redox titration
5:1
How does V2O5 act as a heterogenous catalyst in the contact process?
SO2 reacts with it to form SO3 and V2O4. Catalyst regenerated by V2O4 reacting with O2. Each of the two steps has a lower activation energy than the uncatalysed single step of just reacting SO2 with O2, and therefore the reaction goes faster.
How do Fe2+ ions acts as a homogenous catalyst for the reaction between [S2O8]2- and I-?
Fe2+ reacts with [S2O8]2- to form sulfate ions and Fe3+ ions. The Fe3+ then oxidises I- to I2. The uncatalysed reaction (forming I2 and sulfate ions) takes place between two negative ions which repel is the Ea is high. Both steps of the catalysed reaction are reactions between oppositely charged ions which attract so their rate of reaction is fast. No electrons in any equation.
Half equation for oxidation of ethanedioate ions
[C2O4]2- -> 2CO2 + 2e-
How do Mn2+ ions autocatalyse the reaction between potassium manganate and ethanedioc acid?
Is essentially thenreaction between manganate ions and ethanedioate ions. Mn2+ ions are formed in this reaction. These can then react with [MnO4]- ions to form water and Mn3+ ions (remember to balance with H+). The Mn3+ ions can react with the ethanedioate ions to form CO2 and Mn2+. No electrons in any equation.
