Transition Metals Flashcards
What are transition metals?
A d-block element forming one or more stable ions with partially filled (incomplete) sub-shell of d-electrons.
What are the exceptions of d-block elements that aren’t described as transition metals?
By definition, a transition metal is one that forms at least one stable ion with a partially full d-shell of electrons.
-Scandium only forms Sc3+, which is 3d0 in all its compounds.
-Zinc only forms Zn2+ (3d10).
As scandium has an empty 3d-orbital and zinc has a full 3d-orbital, they are not considered transition metals and cannot form complex or coloured ions.
What are the chemical properties of transition metals?
- Variable oxidation states
- Colour
- Catalysis
- Complex formation
How is variable oxidation states a feature of transition metals?
Transition metals have more than one oxidation state in their compounds, e.g. Cu(I) and Cu(II). This arises from the similar energies required for removal of 4s-and 3d-electrons.
How is colour a feature of transition metals?
The majority of transition metal ions are coloured, Cu2+(aq) is blue. The electrons in the d-subshell determine this.
How is catalysis a feature of transition metals?
Catalysts affect the rate of reaction without being used up or chemically changed themselves. Many transition metals and their compounds show catalytic activity.
-Iron is the catalyst in the Haber process, vanadium (V) oxide in the contact process and manganese (IV) oxide in the decomposition of hydrogen peroxide.
How is complex formation a feature of transition metals?
Transition elements form complex ions. A complex ion is formed when a transition metal ion is surrounded by ions or other molecules, collectively called ligands, which are bonded to it by co-ordinate bonds.
-E.g. [Cu(H2O)6]2+ is a complex ion that is formed when copper sulfate dissolves in water.
What are the physical properties of transition metals?
-High density
-High melting and boiling points.
-Ionic radii are more or less the same.
The properties don’t gradually change across the period as might be expected.
What is a complex ion?
A metal ion surrounded by coordinately bonded ligands. All transition metal ions can form coordinate bonds by accepting electron pairs from other ions or molecules.
What is a ligand?
An atom, ion or molecule that donates a pair of electrons to a central metal ion. A ligand must have at least one lone pair of electrons to use to form the coordinate bond, and can be neutral or negatively charged. All ligands function as Lewis bases.
What are unidentate ligands?
Ligands that can only form one coordinate bond.
- Ammonia, chloride ions, water
- Although water has two lone pairs, they are so close together that it can only form one coordinate bond.
What are bidentate ligands?
Ligands that can form two coordinate bonds.
-Etanedioate (C2O42-), Ethane-1,2diamine, benzene-1,2-diol.
What are multidentate ligands?
Ligands that can form more than one coordinate bonds (inc. bidentate ligands).
-EDTA (ethylendiaminetetra-acetic acid). EDTA acts as a hexadentate ligand, using long pairs on four oxygen and two nitrogen atoms.
What is chelation?
Complex ions with polydentate ligands are called chelates. Chelates can be used to remove d-block metal ions from solution.
-This is due to the chelate effect.
What is the chelate effect?
The enhanced affinity of chelating ligands for a metal ion compared to the affinity of a similar non-chelating (unidentate) ligands for the same metal.
What is coordination number?
The number of coordinate bonds to ligands that surround the metal ion.
What is the shape of complex ions governed by?
Shape is governed by the number of ligands around the central ion.
- Transition metal ions commonly form octahedral complexes with small ligands (e.g. H2O and NH3).
- They also commonly form tetrahedral complexes with larger ligands (e.g. Cl-).
- Some complex ions also form square planar complexes, such as cisplatin.
- It is common for Ag+ to form linear complexes, e.g. [Ag(NH3)2]+, present in Tollen’s reagent.
Do complex ions form optical isomers?
Organically, optical isomerism is displayed in chiral compounds, but it can also be seen I complex ions due to the planes causing the ions to be non-super imposable.
-This is most likely to occur in octahedral complexes, containing bidentate ligands, like [Ni(NH2CH2CH2NH2)3]3+.
What factors determine the colours of complex ions?
- Oxidation state
- Coordination number and shape
- Type of ligands.
Why are transition metal complexes coloured?
- They are coloured because they have partially filled d-orbitals, making it possible for electrons to move from one d-orbital to another.
- In an isolated transition metal atom, all the d-orbitals are of exactly the same energy, but in a compound, the presence of other atoms nearby makes the d-orbitals have slightly different energies.
- When the electrons move from one d-orbital to another of a higher energy level, they often absorb energy in the visible region of the spectrum, equal to the difference in energy between levels.
- The colour is missing from the spectrum, we see colours that aren’t absorbed.
What is the formula to calculate the energy absorbed by complex ions?
∆E = hν ΔE = energy absorbed h = Planck’s constant (6.63x10^-34Js) ν = frequency of light absorbed (hertz/Hz)
What colours do complex ions appear?
When visible light hits a transition metal, some frequencies are absorbed as electrons jump to the higher orbitals. The frequency absorbed depends on the size of the energy gap.
The rest of the frequencies are reflected. These reflected frequencies combine to make the complement of the colour of the absorbed frequencies.
-Red + green = yellow
-Red + blue = purple
-Blue + green = turquoise.
