TOPIC 15 - TRANSITION METALS Flashcards
Transition metal
is a d-block element that has an incomplete d-subshell as a stale ion
found in btw Gp2 and 3
- lose e- from 4s first
properties of transition metals
- have different oxidative states
- form complexes
- coloured compounds
- acts as catalysts - good catalyst as they exist in variable oxid stats so provide alternative pathways so Gp1 etc not good catalysts
- as well as other metal porperties
why is Sc not a transition metal element?
Sc3+ as a stable ion it’s d block subshell is empty and it only forms Sc3+ ion
Sc - 4s2,3d1
Sc 3+ - 3p6
why is Zn not a transition metal element?
Zn only forms Zn2+ and as it’s stable ion it’s d-subshell is completely filled
- 3d10
zn - [Ar] 4s0,3d10
why do transition metals have variable oxidation states?
4s and 3d orbitals are really close in energy levels - is possible for electrons to be lost from both orbitals easily so remaining electrons can form stable configurations
exceptional e- config
Cr - 24 as a ion 4s1 3d5
Cu - 29 as a ion 4s1 3d10
5 subshells in d = total 3d10
what is a complex ion
a transition metal ion bonded to 1/ more ligands by co-ordinate bonds/dative covalent bonds
ligand def
molecule or an ion that can donate a pair of electrons to the transition metal ion to form a co-ordinate bond
co-ordinate number
the total number of c-ordinate bonds formed between a central metal ion and its ligands
solid wedge
bonds coming out of the plane of the paper
hatched wedge
bonds going behind the plane of the paper
ligands and their charge
H2O = 0 aqua -OH = -1 hydroxo NH3 = 0 ammine Cl - = -1 chloro Cl- ligand is much larger and change in coord no
hexaaquairon(II)
[Fe(h2o)6] 2+
coordinate no = 6
6 dative covalent bonds
tetrachloroferrate (III)
[Fecl4]-
depends on size of ligand that determine the coordinate no
[Cu(NH3)4(H20)2] 2+
tetraammineaquacopper (II)
why is partially filled d-orbital in transition element is responsible for the colour. (e- occupied)
when white light passing through sol. containing transition metal ions some wavlengths of visible light from EM spec are absorbed
colour observed is a mix of wavelength of light that have not been absorbed
complementary colours
absorbs red - look blue/ green
increase in frequency absorbed violet/indigo
the lower the wavelength absorbed 400nm
sol. CuSO4 appears blue
because sol absorbs red/organge region of EM and refelcts/transits blue colour
Sc(III) 4s23d0
is colourless in sol. as there is no partially filled d-orbital for the colour
uses of iron
vehicle bodies to reinforce concrete
uses titanium
jet engine parts
uses of copper
water pipes
example of catalysts in transition metals
iron - harber process
vanadium oxide - contact process
MnO2 - decompo H2O2
how colour emitted
movement of lower energy e- to higher energy level = promotion
- the amount of energy it absorbs depends on the difference in energy btw the two levels - bigger diff, more energy ab
energy gained by electron directly prop to freq of absorbed light and inversely prop of the wavelength
shape of complex
octahedral
6 ligands
e- donated 12
bond angle 90
[Co{NH3)6]2+
Mn[OH2] 2+
Al[OH] 3-
Fe[oh2(h20)4]tetrahedral
4 ligands
8 electrons donated
109.5
[CuCl4]2-
linear
2 ligands
4 e- donated
180
[Ag(NH3)2]+
ions and complexes are colourless
no available electrons to excite and move around cannot absorb light = colourless
square planar complexes
Pt and Ni bond angle 90 only 4 coordinate bonds
- cisplatin isomer = Ptcl2nh32 - side effcts so given small amounts and cure cancer therapy not given as a single isomer and not in a mixture with trans form
monodentate ligand
can form 1 coordiante bond per ligand
bidentate
have 2 atoms with lobe pairs and can form 2 coordinate bonds per ligand
e.g. Cr(C2O4)3]3- ethanedioate
Cr(NH2CH2CH2NH2)3]3+
multidentate
EDTA4- can form 6 coordinate bonds per ligand
4O and 2N to donate
- haemoglobin - o2 transport
CO can form strong coordinate bond with Hb and replace O2
colour change arises in changes of
oxidation state
co-ordinate no
ligand
changing ligand or co-ordinate no will
change the energy split btw d-orbitals and change the freq of light absorbed
chelate effect in terms of entropy
multidentate ligands are favoured as they have greater no. of coordinate binds per ligand
EDTA displaces ligands that form fewer coordinate bonds per molecule so significant increase in entropy - gibbs free energy <0 so reaction is feasible so more stable complex ion is formed
Zn in acidic conditions will reduce VO2+ all the way to V2+
alkaline conditions are required for ions to be oxidised so thats the role of pH
- Zn has more negative electrode pot than V half eq Zn2+ + 2e- = Zn E=-0.76v
colour of VO2 +
yellow
colour of V02+
blue
colour of V3+
green. tin metal Sn reduces VO2+ to V3+
colour of V2+
violet
Ecell value shows that the reduction of V
becomes less favourable as the oxid state of V decreases to the point where V2+ to V3+ oxidation is more favourable than the other way around as it is more +ve compared to -ve
[Ag(NH3)2)]+
linear
tollens reagent to test for aldehyde/ketones
Cr2O7 2- (orange) reduced with zinc in acid conditions as Fe is less strong reducing agent and only reduce to Cr3+
to Cr3+(green) and Cr2+ (blue)
Cr 2+ can form a ligand with
sodium ethanoate - red precip
Cr3+ can be oxidised by hydrogen peroxide in alkaline conditions into
Cr2O7 2-
2CrO4 2- by acidification can turn into
Cr2O7 2-
equilibrium add 2H+ = h20
Acidification cause equil shift to the right so Cr2O7 2- increase
amphoteric metal hydroxides
Cr(OH)3(H2O)3
dissolve in acid - accept protons
+ 3H+ -> [Cr(H2O)6] 3+
Cr(OH)3(H2O)3 with base
+ 3OH- –> [Cr(OH)6]3- + 3H2O
enthalpy change for ligand subst
very small - close to 0 as bonds formed are similar to bonds broken
advantages of catalysts for reactions
- proceed at lower temp and press
- saves energy and valuable resources
heterogenous catalysts
haber process
e- are ransferred to produce reactive intermediate and speed up rate of reaction
e.g. contact process V2O5 (reduced from V5+ to V4+ ) convert SO2 -> SO3
catalytic converters
adsorption use 3d 4s e- to make bonds/ correct orientation/ proximity/ weaken/ desorb from active site
Pt/ Rd/Pd
CO + NO —-> N2 + CO2
advantage of using heterogeneous catalyst
no need for seperatin of products from catalyst
good properties of catalysts
- cant adsorb too strongly
- cant adsorb too weakly not held on for long enogh
increase efficiency of heterogenous catalysts
- increase SA = inc no of active site
- spread onto inert medium
catalyst poisoning
poisoned by impurities (S) which do not desorb and cause block of active site
- increase chemical costs
homogenous catalyst
S2O8 2- + I- where Fe2+ used as catalyst and these negative ions would repel naturally and never react so high Ea which overcome
- form intermediates - low Ea
- homogenous cat its e- pot must lie btw the e- pot of the 2 reactants so reduce reactant with more positive e- pot
form 2SO4 2- + I2
STAGE1 => 2SO42- + 2Fe3+
STAGE2 => 2Fe2+ + I2
autocatalysis
when product of a reaction is also a catalyst for that reaction
graph for autocatalysed reaction
intiallyat concen y-axis the is slow and uncatalysed not as much had been formed. rate inc as catalyst is made ; catalysed react faster and slows down as reactants are used up (MnO4 -) drops
so opposite sigmail curve
- high Ea due to 2 -ve ions
autocatalysis by Mn2+ in titrations of C2O4 2- with Mno4 -
2 MnO4- + 5 C2O42- + 16H+ –> 2Mn2+ + 10 CO2 + 8 H2O
Catalysed alternative route
Step 1 4Mn2+ + MnO4- + 8 H+ –> 5Mn3+ + 4 H2O
Step 2 2Mn3+ + C2O4 2- —> 2Mn2+ + 2 CO2
monitor concen of MnO4 -
using colorimeter measure the intensity of purple
- quicker determination of concen as it does not disrupt the reaction mixture
