Transition Metals Flashcards
What are transition metals?
Metals that can form one or more stable ions with an incomplete d sub-shell
Why are Sc and Zn d-block elements, yet not transition metals?
Their highest energy electron is in the de subshell
Not trabsition metals because do not form an stable ipn with an incomplete d subshell
What are four characteristic properties lf transition metals that arise due to their incomplete d subshell?
Complex formation
Catalytic activity
Variable oxidation states
Formation of coloured ions
What is a complex?
A central metal ion that is surrounded by ligands
What is a ligand?
A molecule or ion that forms a co-ordinate bond with a transition metal, by donating a pair of electrons
What are the three types of ligands?
Monodentate, bidentate, multidentate
What is a monodentate ligand?
A molecule or ion that donates one pair of electrons to the central metal ion to form one coordinate bond
Give four common monodentate ligands, and state where their lone pair of electrons is
Water- on the oxygen
Ammonia- on the nitrogen
Chloride ions- on the chloride
Cyanide ion- on the carbon
What is a bidentate ligand?
Molecules or ions that have two atoms, that can each donate a pair of electrons to the central metal ion to form two different coordinate bonds
What is a multidentate ligand?
A molecule or ion that has more than two atoms that can each donate a pair of electrons to the central metal ion to form more than two coordinate bonds
Give the name of the main multidentate ligand, how many coordinate bonds can ot form?
EDTA 4-
Can form six bonds
What is a coordinate number?
The number of coordinate bonds to the central ion in a complex
What are the four common shapes of complexes, and their bond angles and coordinate numbers?
Octahedral- 90, 6 bonds
Tetrahedral- 109.5, 4 bonds
Square planar- 90/180, 4 bonds
Linear- 180*, 2 bonds
What shape do complexes containing water ligands usually have?
Octahedral
What shape do complexes containing ammonia oigands usually have?
Octahedral
What shape do complexes containing chloride ligands usually have?
Tetrahedral
Why is there a difference between the shape of complexes containing chloride ligands and ammonia/water ligands?
Chlorine ions are much bigger than water or ammonia molecules
What shape do complexes containing copper(I) ligands usually have?
Linear
What shape do complexes containing silver(I) ligands usually have?
Linear
What is the complex product when silver chloride or silver bromide is dissolved in ammonia? What shape complex is it?
[Ag(NH3)3]+
Linear
What transition metals usually form complexes with square planar shapes?
Ni, Pt, Pd
Why do transition metals have coloured ions?
Transitipn metal ions can absorb a certain frequency of visible light
This causes d- subshell electrons to be promoted (as they gain energy)
The remaining frequencies of light are transmitted- and the ion appears this colour
What colour are aqueous copper (II) ions and why?
Blue
Cu 2+ ions absorb certain frequencies of visible light
D electrons are promoted
Remaining frequencies are transmitted in the blue area of the visible spectrum
What is the difference in d- orbital energy between transition metal atoms and in complexes?
In transition metal atoms, all d-orbitals have the same energy
In complexes, the d orbitals split depending on the coordination number. So some orbitals have more energy than others. The orbital split creates an energy gap (ΔE)
What is the frequency of loght absorbed by a transition metal ion dependent on?
The size of the energy gap (ΔE)- which is dependent on the coordination number of a complex
Give the two equations for ΔE, and the units of each measurment
ΔE= h (Js) x v (Hz)
ΔE= h x c (ms-1)/y (m)
What is the equation for frequency of light absorbed? (V)
V= c/ y
= speed lf light/ wavelength
In the equation for frequency, what is the unit for wavelength?
metres
What is the unit for energy gap (ΔE)
Joules
What three factors can affect the colour of transiripn metal complexes?
Coordination numbers
Ligand substitution
Oxidation states of transition metals
How does the change in coordination number affect the colour of a trabsirion metal ion?
The splitting of the d-orbitals is different in octahedrals and tetrahedrals- so changes the energy gap. Change in coordination number changes the shape, and so changes energy gap and frequencies of visible light absorbed/ transmitted
How does the change in ligand affect the colour of a trabsirion metal ion?
Different ligands change the energies lf the d orbitals, so changes the size of the energy gap and therefore the frequencies of visible light transmitted/ absorbed
How does the change in oxidation state affect the colour of a trabsirion metal ion?
As the oxidation state of a transition metal increases, so does the size of the energy gap. So different frequencies of visible light are absorbed/ transmitted
What is a colorimeter?
A type of spectroscopy that measures the amount of light absorbed by a solution, and goves a measure of concentration
How do you find the concentration of an unknown solution, using a colorimeter and a calibration curve?
Create 4/5 standard solutions of known concentrations
Select the filter of the complimentary colour to the metal ion, and measure the absorbance pf the known solutions
Use these results to plot a calobration curve
Compare an unknown solutions absorbance to the curve to find the conc.
When creating a calibration curve, why must 4/5 standard solutipns be made?
Sonthere are enough points to plot the curve, and a line of best fit can be drawn
Why is a filter used in a colorimeter?
The sample will only absorb certain frequencies of visible light. A filter that has a complimentary colour is used so the sample will absorb all the light
