TM Flashcards
Define a transition metal+-
An element that forms at least one stable ion with a partially filled d-sub shell
Characteristic properties of TMs
3CV
complex ion
coloured ions
catalytic properties
variable oxidation states
what is a ligand
A molecule or ion that forms a co-ordinate bind with TM by donating a pair of electrons
what is a complex
A central metal atom or ion surrounded by ligands
What is coordination number
The number of coordinate bonds to the central metal atom or ion
what is a mondentate ligand and examples
each ligand forms one coordinate bond
H2O:
Cl:-
:NH3
-:CN
Property NH3 and H2O ligand and why is this important
Similar in size and are uncharged
Exchange of these two ligands occurs without change of coordination number
Property of Cl lignands
Larger than uncharged ligands so only got 4 around TMs
Have a -1 charge so involve a change in co-ordination number
what is a bidentate ligand and examples
Each ligand forms 2 coordinate bonds
Ethane-1,2-diamine/ 1,2-diaminoethane (bonds form from the two N atoms) (something called ‘en’ ligand)
Ethanedioate ( bonds form from the 2 O- atoms)
what is a multi dentists ligand and examples
Each ligand forms 2 or more coordinate bonds
EDTA4- (forms 6 coordinate bonds, 2 from the N atoms and 4 from the O- atoms)
what is ‘haem’ group
its an iron(ii) complex with a multidentate ligand
what is a ‘globin’
a 5th bond forms to the fe2+ below the ring to a protein which is the globin
what is haemoglobin
a molecule found in red blood cells used to transport oxygen around the body. made up of a central fe2+ ion which has a coordination number of 6. it forms 4 bonds to a ring system called porphyrin. square planar arrangment
how is oxygen transported in the blood
oxygen forms a co-ordinate bond to Fe(II) in haemoglobin
why is carbon monoxide toxic
because it replaces oxygen co-ordinately bonded to Fe(II) in hemoglobin
how does the chelate effect occur and is it
occurs when a monodentate ligand is subsistuted by a bidentate or multidentate ligand.
it results in a large increase in entropy as more moles on RHS of equation due to subsistution (this is the chelate effect)
what is due transition mental usually form with small lignads
octahedral complexes
examples of small ligands
H2O and NH3
what isomerism can octahedral complexes display with monodentate lignads
cis-trans isomerism
what isomerism can octahedral complexes display with bidentate lignads
optical isomerism
stereoisomerism definition
have the same structural formula but have a different arrangement of atoms in space
what is cis-trans isomerism
where ligands can be spaced in different positions relative to one another. its a special case of E-Z isomerism. for example if you have 4of one type of ligand and 2 of another the 2 ligands that are the same can be arranged either at 90 degrees (next to each other) which displays cis isomerism or 180 degrees (opposite) which displays trans isomerism.
what do transition metals commonly form with larger ligands
tetrahedral complexes
examples of larger ligands
cl-
what is less commonly formed by transistion metals with larger ligands
square planar complexes
what isomerism does square planar display
cis-trans isomerism
how to tell if trans isomer or cis isomer in sqaure planar complex
if alike ligands are opposite to one another then it is trans isomer
if alike ligands ligands are next to each other then its cis isomer
what is cisplatin
cis isomer of [PtCl2(NH3)2]
cisplatin use
very effective anti-cancer drug, it works by binding to the DNA in cancerous cells and stops cell replicating
the 2 Cl- ions on the cisplatin are substituted for the two N atoms on the adjacent Guanine bases
when does the cis isomer display optical isomerism
when has at least 2 bidentate ligands
what is tollens reagent complex ion
[Ag(NH3)2]+ Ag+ forms the linear complex
how are transition metals identified
by thier colour
how does colour arise in transistion metals
when some of the wavelengths of visible light are absorbed and the remaining wavelengths of light are transmitted or reflected
what happens when light is absorbed in transition metals
d electrons move from the ground state to an exited state when light is absorbed
what is the energy and length or wavelength of colors in white light
ROY = lower energy, longer wavelength
G
BIV- higher energy, shorter wavelength
the frequency of light which provides the change in energy between 2 d subshells can be found by the formulas:
change in energy(J)= hf or = h(c/wavelength of light)
where
h= planck constant Js
and f = frequency of light s-1
c= speed of light
if a transition metal compounds has a large energy change between d subshells then
BIG E BIV abs
high energy light(BIV)
will be absorbed to excite electrons
ROY will be reflected so compounds will look red/orange
if a transition metal compounds has a small energy change between d subshells then
small E ROY abs
low energy light (ROY)
will be absorbed to exite electrons
BIV will be reflected by the compound
so compound will look blue/ pourple
what changes can alter the colour of the TM compumd
LOCo
change in ligands
change in oxidation state of the metal
change in coordination number of the complex
where is the absorption of visible light used
spectometry
what is a simple colorimeter used for
to determine the concentration of coloured ions in the solution
how to find the concentration of an unknown sample from the calibrations curve
measure the absorbance of known conc
plot graph absorbance v conc
read value conc for measured absorbance
from this graph
lower oxidation states and higher oxidation states types of ions
lower oxidation states exist as simple ions
higher oxidation states only form as ‘polyatomic’ ions eg manganese in the (VII) exists as the manganate ion MnO4-
reduction of vanadium species
vanadate(V) ion reduced to (VO3)- or (VO4)3- or (VO2)+
in acidic conditions by solid Zinc which itself is oxidised Zn —> Zn2+ +2e-
what is the redox potential for transition metals ion changing from a higher to a lower oxidation state influenced by
pH (larger in acidic solutions, some need H+ to be reduced some others releases OH- when reduced) and by the ligand(different ligands may make the redox potential larger or smaller depending on how well they bind to a particular metal ion in a particular oxidation state)
colour change Fe2+ to Fe3+
green to brown
colour change MnO4- to Mn2+
purple to colourless
(Cr2O7)2- to Cr3+ colour change
orange to green
what is the redox potential of on ion or atom
how easily it is reduced to a lower oxidation state
how does tollens reagent use redox to distinguish between aldehydes and ketones
prepared by adding just enough ammonia solution to silver nitrate solution to form colorless solution containing the complex ion [Ag(NH3)2]+ when added to aldehyde tollens reagent reacts to give a silver mirror, by the aldehyde is oxidized to carboxlilic acid and Ag+ ions are reduced to silver metal
what is a catalyst
speeds up rate of reaction and doesn’t get used up in reaction. works by providing an alternative reaction pathway with a lower activation energy
transition metals and their compounds can act as
heterogenous and homogenous catalysts
what is a heterogeneous catalyst
is in a different phase from the reactants and the reaction occurs at the active site on the surface
what is a homogenous catalyst
in the same phase as the reactants and reaction proceeds through an intermediate species
mechanism steps of heterogeneous catalyst
reactants adsorb onto the surface of the catalyst on an active site
reaction occurs on the surface of the catalyst
products desorb from the surface of the catalyst
how to make heterogenous catalyst more effecient
increase surface area
spread the catalyst over an inert support medium
why don’t heterogeneous catalysts last forever and how increases time they last
posisoning can occur
impurities can block the active sites
this prevents the reactants from adsorbing
purifying the reactants if the best way to prevent to poisinging
catalyst for making ammonia in Haber process and the eqaution
catalyzed by solid iron heterogenous
N2(g) + 3H2(g) <—> 2NH3(g)
heterogenous catalyst for making sulphric acid in the contact process and the equations
heterogenous catlayste solid vandium(V) oxide - V2O5(s)
1- SO2(g) + V2O5(s) <—-> SO3(g) + V2O4(s)
2- 2V2O4(s) + O2(g) <—> 2V2O5(s)
overall- 2SO2(g) + O2(g) —> 2SO3(g)
sulfuric acids then formed by reacting SO3 and H2O
catalyst for making methanol
Cr2O3
heterogenous
why in homogenous catlyst is the activation energy of the uncataluysed reaction so high
the two negative ions repel
catatlyse for reaction of I- and (S2O8)2-
eqautions and why
Fe2+ (homogenous) needs catalyst as both negative
(S2O8)2- (aq) + 2Fe2+(aq) –> 2(SO4)2-(aq) + 2Fe3+(aq)
2I-(aq) +2Fe3+(aq) —> I2(aq) + 2Fe2+(aq)
overall equation
(S2O8)2-(aq) + 2I- –> 2(SO4)2-(aq) +I2
what is autocatalysis
unusual example of homogeneous catalysis, where one of the products of the reaction actually catalyses’ the reaction as it proceeds further
autocatalysis example in oxidation of ethanedioic ions
by mangate(VII) ions
explain with the aid of eqautions how reaction between manganite (VII) ions and ethanedioate ions are catalysed
Uncatalysed reaction very slow :
2MnO4- +16H+ + 5C2O4 2- —-> 2Mn2+ +8H2O + 10CO2
Quickens as reaction proceeds as Mn2+ formed acts as autocalyst, reacts with MnO4- ions to form Mn3+ as an intermediate species
4(Mn)2+(aq) + MnO4-(aq) + 8H+(aq) –> 5Mn3+(aq) + 4H2O(l)
which then reacts with C2O4 2- ions to reform Mn2+
2Mn3+ (aq) + (C2O4)2-(aq) —> 2CO2(g) + 2Mn2+(aq)
describe and explain the conc vs time graph for reaction between MnO4- and C2O4 2
the rate starts off slow as there is no catalyst initially.
the 2 negatively charged reactants collide with a very high Ea
then as some Mn2+ is formed the rate increases as the reaction is being increasingly catalyzed.
the rate then decreases and levels off as the reactants get used up
