Transition Metals Flashcards
Define ligand
A ligand is a molecule or ion that forms a coordinate bond with a transition metal by donating a pair of electrons
Define complex
A complex is a central metal atom or ion surrounded by ligands
Define coordination number
Number of coordinate bonds to the central metal atom or ion
Define transition metals
A transition element is one that forms at least one stable ion with a partially filled d sub-shell
What are the key features of transition metals
1 - form complex ions
2 - coloured ions
3- catalytic properties
4 - variable oxidation states
Define coordinate bond
A shared pair of electrons which have both come from the same atom
Give examples of monodentate ligands, bidentate ligands and multidentate ligands
Monodentate - H2O, NH3, Cl-, CN-
Bidentate - H2NCH2CH2NH2 (ethane - 1,2 - diamine) and C2O42- (ethanedioate)
Multidentate - EDTA4-
Define monodentate, bidentate and multidentate ligand
Monodentate - Each ligand forms 1 coordinate bond
Bidentate - each ligand forms 2 coordinate bonds
Multidentate - each ligand forms 2 or more coordinate bonds
What are the four common shapes which transition metals complexes form and give examples
Octahedral - 6 coordinate bonds - H2O and NH3 (e.g. [cu(H2O)6]
Tetrahedral - 4 coordinate bonds - Cl- (e.g.CuCl42-)
Square planar - 4 coordinate bonds - CN- [Ni(CN)4]2- OR cis platin (e.g. [Pt(Cl2)2(NH3)2]
Linear - 2 coordinate bonds - Ag (e.g. [Ag(NH3)2]+
Show how the complex [Cu(H2O)6]2+ can be converted into [Cu(H2O)3(NH3)3]2+
[Cu(H2O)6]2+ + 3NH3 ————> [Cu(H2O)3(NH3)3]2+ + 3H2O
What is the chelate effect
When a monodentate ligand is substituted by a bidentate ligand or a multidentate ligand
Explain why this reaction is feasible when changing [Cu(NH3)6]2+ to [Cu(H2NCH2CH2NH2)3]2+
There are 4 moles on the left
There are 7 moles on the right
There has been an increase in entropy
Delta S is more positive
Delta H is zero as same number of bonds are being broken and formed
Haemoglobin
O2 forms a coordinate bond to Fe2+ in haemoglobin enabling oxygen to be transported in the blood
CO is toxic because CO bonds more strongly to the Fe2+ in haemoglobin
This prevents O2 from bonding to the Fe2+, causing suffocation
Stereoisomers
Same structural formula but different arrangement of atoms in space
Cis and trans
Cis - same side - displays optical isomerism mirror image
Trans - opposite sides
What does cis platin do
Binds to DNA in cancer cells and stops cell replication
Why are transition metals coloured (example blue)
1 - Transition metals are coloured because they have partially filled d subshells
2 - These electrons absorb a specific amount of energy from visible light and transmit the rest of the colours
3 - These d subshells electrons become excited and move from ground stable state to unstable state
ROY is mostly absorbed
BIV is transmitted
What is the energy for the different colours
SMALL E ROY - low energy - long wavelength
BIG E BIV - high energy - short wavelength
What is delta E
Difference in energy between ground state and excited state
What are the 2 equations for delta E
Delta E = hv
Delta E = h(c/wavelength)
H = plancks constant
V = frequency of light
If there is a change to delta E it can change the colour of the compound. What things can change the colour
Change in ligand
Change in oxidation state
Change in coordination number
Change in shape
Writing frame for if it is a red solution
If has a large delta E between d subshells
High energy light BIV will be absorbed to excite electrons
ROY is reflected
This means co pound will look red
Key points of calorimetry
Measure absorbance for a range of known concentrations
Plot a graph of absorbance against concentration
Read the value of the concentration for the measured absorbance from the graph
Heterogenous catalyst vs homogenous catalyst
Heterogenous - catalyst is in a different phase to the reactants
Homogenous - where the catalyst is in same phase as the reactants
Mechanism for heterogenous catalysts
1) Reactants aDsorb (stick to) onto the surface of catalyst on active site
2) reaction occurs on the surface of that catalyst
3) Products desorb from the surface of the catalyst
Homogenous catalyst example you need to know
S2O82- + 2I- ————> 2SO₄²- + I2
Reaction is catalysed by Fe2+ ions
Combine redox reactions for S2O8- ——> SO₄²- and Fe2+ ——> Fe3+
Step 1: S2O82- + 2FE2+ ————> 2SO₄²- + 2Fe3+
STEP 2: combine redox reaction for I- ———> I2 and Fe3+ ———> Fe2+
2I- + 2Fe3+ ———> I2 + 2Fe2+
What is autocatalysis
Where one of the products of the reaction actually catalyses the reaction as it proceeds further.
Autocatalysis example you just know
Combine redox reaction of MnO4- ———> Mn2+ and C2O42- ——> CO2
Uncatalysed reaction : 2MnO4- + 16H+ 5C2O42- ———> 2Mn2+ 8H2O + 10CO2
Mn2+ catalyse reaction in 2 step process. Initially rate is slow but as more catalyst produced the rate increases.
Step 1: combine the equation of MnO4- to Mn2+ and Mn2+ to Mn3+
4Mn2+ + MnO4- + 8H+ ———> 5Mn3+ +4H20
Mn2+ oxidised by MnO4- to Mn3+
Step 2: combine equation of Mn3+ to Mn2+ and C2O42- TO CO2
2Mn3+ + C2O42- ———> 2CO2 + 2Mn2+
Describe the concentration vs time graph for autocatalysis of MnO4-
1- Rate starts off slow as there is no catalyst initially
2- The two negatively charged reactants collide with very high Ea
3 - Then as some Mn2+ is formed the rate increases as the reaction is being increasingly catalysed
4- The rate then decreases and levels off as the reactants get used up
