Transition Metals Flashcards
Transition element definition
A transition element is a d-block element that can form at least one stable ion with a partially filled (incomplete) d sub-shell.
The d sub shell can hold up to how many electrons?
10
Across period 4, which elements have an unusual electron configuration and why?
chromium and copper because an electron from the 4s orbital moves into the 3d orbital to create a more stable half full or full 3d sub shell respectively
Which two elements across period 4 are d block elements but not transition elements?
scandium and zinc
Why is scandium not a transition element?
It forms only one stable ion of Sc 3+. Sc 3+ has an empty d sub-shell and as it is not partially filled it is not a transition element.
Why is zinc not a transition element?
It forms only one stable ion of Zn 2+. Zn 2+ has a full d sub-shell. As it is not partially filled, it is not a transition element.
Why do transition metals have variable oxidation states?
The electrons sit in 4s and 3d energy levels which are very close. As a result, electrons are gained and lost using a similar amount of energy.
What colour is V 2+ (aq)?
violet
What colour is V 3+ (aq)?
green
What colour is VO 2+ (aq)?
blue
What colour is VO2 + (aq)?
yellow
What colour is Cr 3+ (aq)?
violet when surrounded by 6H2O but they are normally substituted so usually looks green
What colour is Cr2O7 2- (aq)?
orange
What colour is Mn 2+ (aq)?
pale pink
What colour is MnO4 - (aq)?
purple
What colour is Fe 2+ (aq)?
pale green
What colour is Fe 3+ (aq)?
orange/yellow
What colour is Co 2+ (aq)?
pink
What colour is Ni 2+ (aq)?
green
What colour is Cu 2+ (aq)?
blue
What is a complex ion?
where a central transition metal ion is surrounded by ligands bonded by dative covalent (coordinate) bonds
What is a ligand?
an ion, atom or molecule that has at least one lone pair of electrons
What are monodentate ligands?
ligands which only have one lone pair of electrons (can also be called unidentate ligands)
What are three examples of monodentate ligands?
H2O:
:NH3
:Cl-
What are bidentate ligands?
Ligands which have 2 lone pairs of electrons
What are two examples of bidentate ligands?
Ethanedioate
Ethane-1,2-diamine
What are multidentate ligands?
Ligands which have more than 2 coordinate bonds
What are two examples of multidentate ligands?
Haem and EDTA 4-
How many coordinate bonds can EDTA 4- make with the central metal ion?
6
What is the shape of a complex ion dependent on?
the size of the ligands and the coordination number
What is the coordination number?
the number of coordinate bonds in a complex
Give two examples of small ligands that you can fit 6 of around a central metal ion
H2O:
:NH3
Give an example of a larger ligand that you can only fit 4 of around a central metal ion
:Cl-
How many molecules of ethanedioate/ethane-1,2-diamine can you fit around a central metal ion usually?
3
Complexes with a coordination number of 6 form what shape?
octahedral
What is the size of all the bond angles in an octahedral complex?
90 degrees
Complexes with a coordination number of 4 form what shapes?
tetrahedral and square planar
What are the bond angles in a tetrahedral complex?
109.5 degrees
Give a specific example of a square planar complex
the anti-cancer drug cis-platin Pt[(NH3)2(Cl)2] (aq)
Give two examples of complexes with an octahedral shape
Co[(H2O)6] 2+ Co[(NH3)6] 2+
Give an example of a complex with a tetrahedral shape
[CuCl4] 2-
Complexes with a coordination number of 2 form what shape?
linear shapes
Give an example of a complex with a linear shape
[Ag(NH3)2] + (Tollen’s reagent)
What are the bond angles in a linear complex?
180 degrees
What is the name of the multidentate ligand in the molecule haemoglobin?
haem
What is the transition metal ion in haemoglobin complex?
Fe 2+
What is the shape of the complex ion in haemoglobin?
octahedral
What is the coordination number of the complex ion in haemoglobin?
6
What forms 4 of the coordinate bonds in the complex ion in haemoglobin?
4 nitrogens which come from a tetradentate ligand
In the complex ion in haemoglobin, what forms another coordinate bond?
one of the coordinate bonds comes from a large protein called globin
Where does the final coordinate bond come from in a haemoglobin complex?
it can bind loosely to an oxygen molecule
What happens to haemoglobin when in the lungs where the oxygen concentration is high?
oxygen substitutes the water ligand to form oxyhaemoglobin
What happens to oxyhaemoglobin when oxygen is needed?
Oxyhaemoglobin gives up oxygen to a place where it is needed. Water takes the place and haemoglobin returns back to the lungs to start the process again.
What is carbon monoxide?
a poisonous gas that causes headaches, unconsciousness and even death - it is odourless and colourless
What happens if carbon monoxide is inhaled?
The water ligand (on the complex ion in haemoglobin) is replaced with a carbon monoxide ligand. Carbon monoxide bonds strongly so it’s not readily replaced by oxygen or water. This means oxygen can’t be transported and leads to oxygen starvation in organs. Hence why carbon monoxide is poisonous.
Do complex ions show optical isomerism?
Yes
What is the criteria for a complex ion to show optical isomerism?
octahedral complex with 3 bidentate ligands
Do complex ions show cis-trans isomerism?
Yes
What is the criteria for an octahedral complex ion to show cis-trans isomerism?
octahedral complex with 4 ligands of the same type and 2 ligands of a different type
How do you know if an octahedral complex ion is a trans isomer?
It is octahedral shape with 4 ligands of the same type and 2 ligands of a different type. The two different ligands will be opposite each other.
How do you know if a complex ion is a cis isomer?
It is octahedral shape with 4 ligands of the same type and 2 ligands of a different type. The two different ligands will be adjacent to each other.
As well as octahedral shape complex ions, what other shape can display cis-trans isomerism?
square planar complex ions
How do square planar complexes show cis-trans isomerism?
They have two ligands of the same type and two ligands of a different type. If the two different ligands are opposite each other, you have a trans isomer but if the two different ligands are adjacent to each other, you have a cis isomer.
Give the formula of the ‘platin’ complex that is an anti-cancer drug
Cis-[Pt(NH3)2Cl2] (aq)
When does the d-subshell split into 2?
when ligands bond with the central metal ion
What is created when we attach ligands and some orbitals gain energy?
an energy gap
What happens when electrons absorb light energy?
some move from the lowest energy level (ground state) to higher energy level orbitals (excited states)
What must the energy from light equal in order for electrons to move from lowest energy level to higher energy orbitals?
the energy from light must equal the energy gap ΔE
What does the size of ΔE depend on?
- the central metal ion and its oxidation state
- the type of ligands
- coordination number
What is the formula for calculating the energy absorbed by the electrons? and what is the variation on this formula?
ΔE = hv
h = Planck’s constant
v = frequency of light absorbed (Hz)
ΔE = change in energy (J)
ΔE = (hc)/λ
c = speed of light (3 x 10^8 ms-1)
λ = wavelength of light absorbed (m)
On a spectrum, what colour has the lowest frequency?
red
On a spectrum, what colour has the highest frequency?
violet
The larger the energy gap, the ________ the frequency of light absorbed
higher
What happens to the frequencies of light that are not absorbed?
they are reflected or transmitted (these make a complimentary colour that we see)
What colour do we see complexes that have a full or empty 3d sub shell and why?
no electrons can migrate to the higher energy level which means we see these complexes as colourless or white
Give an example of ligand substitution where the coordination number is the same but the colour of the complex changes due to the new type of ligand
[Co(H2O)6] 2+ + 6NH3 -> [Co(NH3)6] 2+ + 6H2O
complex is originally pink whereas after ligand substitution the complex is now straw-coloured
Give an example of ligand substitution where the coordination number changes
[Cu(H2O)6] 2+ + 4Cl - -> [CuCl4] 2- + 6H2O
originally the complex is pale blue but after ligand substitution which changes the shape of the complex the colour of the complex is now yellow
Give two examples where the complex colour changes but only the oxidation state has changed
[Fe(H2O)6] 2+ -> [Fe(H2O)6] 3+
originally the complex is pale green but after the complex colour is yellow
[V(H2O)6] 2+ -> [V(H2O)6] 3+
originally the complex is violet but after the complex is green
What is colorimetry used for?
used to measure the concentration of transition metal ions in solution
How does a colorimeter work?
A colorimeter measures the absorbance of light by a coloured sample. The more concentrated a sample is, the darker it’s colour and hence the more light absorbed.
How do you use a colorimeter?
- The colorimeter must be set to zero. To do this we measure the absorbance of a blank sample. A blank sample is normally the solvent you are using to dissolve your transition metal ion (normally water).
- White light is filtered into a narrow range of frequencies. Monochromatic light (single colour) is produced. The choice of filter is important. The colour produced from the filter must be absorbed by the metal ion solution.
- The monochromatic light passes through the sample and some of the light is absorbed. The sample is held in a vessel called a cuvette.
- Light not absorbed travels to the detector. The detector will measure the level of absorbance by comparing it to the absorbance of the blank sample.
After using a colorimeter, how do we find out the concentration of the sample?
By plotting a calibration curve and then test the sample we want to know the concentration of by measuring the absorbance and then reading across the graph to find the concentration
How is a calibration curve made?
making up a range of known different concentrations of the transition metal ion solution and the absorption is measured for each one and the results are plotted
Give an example of a partial ligand substitution reaction that still results in a complex colour change
[Cu(H2O)6] 2+ + 4NH3 -> [Cu(NH3)4(H2O)2] 2+ + 4H2O
originally the complex is blue but after partial substitution the complex colour is dark blue
Give 3 examples of ligands of a different size being exchanged and their complex colours
[Co(H2O)6] 2+ + 4Cl- -> [CoCl4] 2- + 6H2O
originally the complex is pink but after the complex is blue
[Cu(H2O)6] 2+ + 4Cl- -> [CuCl4] 2- + 6H2O
originally the complex is blue but after the complex is yellow
[Fe(H2O)6] 3+ + 4Cl- -> [FeCl4] - + 6H2O
originally the complex is yellow and after the complex is still a yellow colour but the complex has changed shape from octahedral to tetrahedral
