transition metals Flashcards
What is a transition element?
A d-block element that can form at least one stable ion with a partially filled d-subshell.
What are the general physical properties of transition metals?
- Good conductors of heat and electricity
- Hard
- Strong
- Shiny
- High melting points
- High boiling points
What are the general chemical properties of transition metals?
- Form complex ions
- Form coloured ions
- Good catalysts
- Variable oxidation states
What is the order of filling electron subshells in transition metals?
4s sublevel fills up first, followed by the 3d sublevel.
Which two elements are exceptions in the electron configuration pattern of transition metals?
Chromium (Cr) and Copper (Cu).
Why are Scandium and Zinc not considered transition metals?
They only form Sc3+ (3d10) and Zn2+ (3d10) respectively, resulting in empty or full d subshells.
What is a complex ion?
A transition metal ion surrounded by ligands bonded to it by coordinate bonds.
What defines a ligand?
A molecule or ion that forms a coordinate bond with a transition metal by donating a pair of electrons.
What is the coordination number?
The number of coordinate bonds to ligands that surround the d-block metal ion.
What are the types of ligands based on coordination?
- Uni/Monodentate ligands
- Bidentate ligands
- Multidentate ligands
What is the chelate effect?
The phenomenon where monodentate ligands are replaced by bi/multidentate ligands, forming more coordinate bonds.
What is the shape of octahedral complexes?
Coordination number of 6 with bond angles of 90 degrees.
How does the substitution of similar sized ligands occur?
Without change of coordination number or shape.
What happens during the substitution of different sized ligands?
Change of coordination number and shape occurs.
What is the effect of ligand substitution on enthalpy?
Enthalpy change is often small as the strength of the bonds broken is similar to the new bonds formed.
What is the significance of multidentate ligands in stability?
They form more stable complexes due to ring structures, which are thermodynamically and kinetically stable.
What is optical isomerism?
Occurs when there are two or more bidentate ligands in a complex that is octahedral.
Why are transition metal complexes colored?
Due to their partially filled d-orbitals allowing electrons to be promoted by absorbing UV/visible light.
What is the formula for calculating ΔE?
ΔE = hν = hc/λ
What does a high frequency of light correspond to in terms of color?
Violet light, which has high energy.
What is the overall charge on a complex ion determined by?
The total oxidation state of the metal ion and the sum of the ligand charges.
What is the bond angle in tetrahedral complexes?
109.5 degrees.
What is the bond angle in square planar complexes?
90 degrees.
Fill in the blank: A ligand that forms 1 coordinate bond to a metal ion is called a _______ ligand.
monodentate
True or False: All transition metals are highly reactive.
False
What is the relationship between frequency and color of light?
Frequency is related to the color of light.
Violet is of high energy and frequency, while red is of low energy and frequency.
What does the color of a transition metal complex depend on?
The color depends on the energy gap ΔE, which is influenced by the oxidation state of the metal and the ligands.
Different compounds of the same metal can exhibit different colors.
What is the oxidation state and color of V2+ in water?
V2+ is violet in color.
This is one of the colors of ions when dissolved in water.
What is the oxidation state and color of Mn2+ in water?
Mn2+ is pale pink in color.
What is the effect of ligands on the color of transition metal complexes?
Ligands affect the energy gap ΔE and thus influence the color of the complex.
How does spectroscopy determine the concentration of a solution?
By measuring the amount of light absorbed by the solution.
More concentrated solutions absorb more light.
What is colorimetry used for?
To measure the amount of light of a particular wavelength that passes through a colored solution.
What happens to light transmission in a more concentrated solution?
Less light is transmitted through the solution, more is absorbed.
What is the main feature of a colorimeter?
It uses a light source and a detector to measure light absorption.
A calibration graph is used to determine concentration.
What defines variable oxidation states in transition metals?
Transition metals can use their 3d and 4s electrons in bonding, leading to a variety of oxidation states.
Which transition metals show both +1 and +2 oxidation states?
All except scandium and zinc show both +1 and +2 oxidation states.
What is the reagent used for testing aldehydes?
Tollen’s reagent - contains [Ag(NH3)2]+.
What is the color change observed in Fehling’s solution when testing for aldehydes?
A brick-red precipitate (Cu2O) is formed.
What is the color change when primary and secondary alcohols are oxidized using acidified K2Cr2O7?
Color changes from orange (Cr2O72-) to green (Cr3+).
What is the definition of oxidation in redox reactions?
Loss of electrons.
What is the definition of reduction in redox reactions?
Gain of electrons.
What is an oxidizing agent?
An electron acceptor that is reduced.
What is a reducing agent?
An electron donor that is oxidized.
What factors affect the ease of changing oxidation states in transition metals?
pH and ligands present.
What is the effect of pH on oxidation and reduction of transition metals?
Easier to oxidize in alkaline conditions; easier to reduce in acidic conditions.
What is the significance of electrode potentials in redox reactions?
They are affected by ligand type and pH, influencing oxidation and reduction ease.
What is the color of V2+ in acidic conditions?
V2+ is violet.
This occurs when V is reduced from V(+5).
What is the self-indicating property of KMnO4 in redox titrations?
It changes from purple to colorless when reacted, indicating the endpoint.
What is the overall equation for the reaction of Fe2+ with KMnO4?
5Fe2+ + MnO4- + 8H+ → 5Fe3+ + Mn2+ + 4H2O.
What is autocatalysis?
A reaction where one of the products acts as a catalyst.
What is a catalyst?
A substance that increases the rate of a chemical reaction without being used up.
What are heterogeneous catalysts?
Catalysts that are in a different phase from the reactants.
How do heterogeneous catalysts work?
Reactants are adsorbed onto the surface, increasing reaction likelihood.
What is catalyst poisoning?
When substances adsorb strongly to the surface, blocking active sites and lowering efficiency.
What is the effect of increasing the surface-to-mass ratio in catalysts?
It reduces costs as only a small coating is required for large surface area
This is particularly beneficial for expensive catalysts.
What is catalyst poisoning?
When other substances adsorb strongly to the surface of a catalyst, blocking active sites
This lowers the efficiency or makes the catalyst ineffective.
What is an example of catalyst poisoning in the Haber process?
Sulfur poisoning due to sulfur impurities in natural gas
Any sulfur adsorbed onto the Fe catalyst stops it from working efficiently.
What is the catalyst used in the Haber process?
Fe catalyst
The iron catalyst lasts about five years before it becomes poisoned.
What is the role of vanadium(V) oxide in the Contact process?
It oxidizes sulfur dioxide to sulfur trioxide
The vanadium(V) oxide is regenerated unchanged after the reaction.
What type of catalyst is a homogeneous catalyst?
A catalyst that is in the same phase as the reactants
Most reactions involving homogeneous catalysts take place in solution.
How do homogeneous catalysts work?
They proceed via an intermediate species formed from a reactant and the catalyst
The intermediate reacts further and regenerates the catalyst.
What is the role of an acid homogeneous catalyst?
It protonates one of the reactants
This leads to the formation of a species that reacts with another reactant.
What is an example of a transition metal homogeneous catalyst?
Fe2+ ions catalyzing the oxidation of iodide ions to iodine
This reaction is very slow without the catalyst due to repulsion between negative ions.
What is autocatalysis?
When one of the products of the reaction is a catalyst for the reaction
The reaction starts slowly and speeds up as the concentration of the catalyst increases.
What is the significance of variable oxidation states in transition metals?
They allow transition metals to gain/lose electrons from their d orbitals
This enables them to act as effective catalysts by facilitating redox reactions.
In the catalyzed reaction of ethanedioic acid by manganate(VII) ions, what role do Mn2+ ions play?
They act as a catalyst
Mn2+ can easily change between oxidation states, facilitating the reaction.
What happens in the reaction catalyzed by Mn2+ ions?
Mn2+ reduces MnO4- to Mn3+, which then oxidizes C2O4 2- to CO2
The reaction leads to the regeneration of Mn2+.
Fill in the blank: The vanadium(V) oxide in the Contact process is used to manufacture _______.
concentrated H2SO4
True or False: The iron catalyst in the Haber process can last indefinitely without replacement.
False
