transition metals Flashcards
what is a transition metal
an element that forms at least one stable ion with a partially filled d sub shell
what 4 key features do transition metals display
1) form complex ions
2) coloured ions- transition metal compounds are diffrent colours
3) catalytic properties- transition elements and compounds formed from transition events can act as catalysts
4) variable oxidation states
transition elements form compounds in which the metal can have different oxidation states
what is a coordinate bond
shared pared of electrons that come from the same ion
what is a ligand
an ion or molecule with a lone pair of electrons that can from a coordinate bong
what is a bidentate ligand
2 coordinate bonds in a ligand
coordination number
number of coordiante bonds
what is a complex ion
centeral atom surrounded by ligands
multi dente ligand
2 or more coordinate bonds formed
name 5 monodente ligands
water H2O:
ammonia :NH3
hydroxide -:OH
chloride Cl:-
cynaide -:CN
name two bidentate ligands
ethane-1,2-diamine
:NH2CH2CH2NH3:
ethanedioate ion
C2O4-2
why does chloride ligands only fit 4 around
relatively large
how many coordinate bonds can EDTA4- form
6
2 form N atoms
4 from O atoms
when does the chelate effect occur
when a monodente ligand is substituted by and bidente ligand or multi dente ligand
AND THERE IS A LARGE INCREASE IN ENTROPY
explain why ligand substation reactions are feasible
more moles of products then reactants
so increase in entropy/disorder
same amount of bonds broken as formed
^H IS APPROXIMATELY ZERO
^G is less then or exalt to zero making reaction feasible
how is suffocation caused by coordinate bonds
O2 forms a coordinate bond to Fe2+
in hameoglobin enabling oxygen to be transported in the blood
CO is toxic because CO bonds more strongly to Fe2+ in hameglobin
this prevents O2 from forming bonds causing suffocation
want is a stereoisomer
same structural formula but a diffrent arrangement in space
trans isomer
2 ligands arranged opposite to each other
what is a cis isomer
two ligands arranged next to each other
why is Cis platin an anti cancer drug
binds to the DNA in cancer cells and stops cell replication
preventing growth and spread of cancer cells
how do you find out which optical isomer is present
optical isomers rotate a plane of polarised light in opposite directions
describe the energy of diffrent colours of light
ROY -low energy
G
BIV- high in energy
why do transition metal compounds appear coloured
they have partially filled 3d subshells
in a transition metals all d orbitals are equal in energy (GROUND STATE)
the presence od other atoms causes the d orbitals to have slightly diffrent energies
this enables electrons to be excited from one d subshel to another
when an electron moves from a low energy subshel to a higher one the energy needed to make the transition is taken from white light
the colour of the light absorbed is then missing from the light which is reflected
the colours are transmitted give the compound is colour
change in E can be found using what formula
^E=hv
^E is change in energy gained by the excited electron
h is planks constant
v is frequency of light
explain big E BIV absorption
large increase in energy between d sub shells
high energy light absorbed to excite electrons
red orange yellow reflected
so looks red orange
what things can alter the colour of a compound
change in
ligands
oxidation state
coordination number
shape of a complex
what does colorimetry do
determine the unknown concentration of transition metal ions
by measuring the amount of lights transmitted threw a sample
describe the experimental method
an appropriate ligand is added to solution in order to intensify colour
a range of solutions of same complex ion are made of known concentrations
one at a time they are tested in a colorimeter the transmission is measured
a graph is plotted of conc vs transmission and line of best flirt drawn
the transmission of unknown solution is measured in a colorimeter and it’s concentration is determined by a reading off the calibration curve
what affects the amount absorption in the experimental method of measuring absorpion
length of container the solution is in
diluted
filters used in the colorimeter which allows one colour of light threw the sample
how do you calibrate in order to measure absorption of unknown solution
cuvette is filled with water and put in the colorimeter and set to zero
this ensure accuracy and negated absorbsnce due to solution
what is a catalyst
a substance that increases the rate of a chemical reaction without being used up
how does a catalyst work
provides an alternative reaction pathway with a lower activation energy
what is a heterogeneous catalyst
diffrent phase to reactant
what is a homogeneous catalyst
same phase an the reactants
how do heterogenous catalysts work
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 do you make a catalyst most effectent
increase surface area
spread the catalyst over an inert support medium
how can poison of catalyst occur
impurities blocking the active sites
prevents the reactants from adsorbing
purifying the reactants in the best way to prevent poisoning
name 3 heterogeneous catalyst examples
making ammonia in the haber process
catalysed by solid iron
making sulfuric acid in the contact process
catalysed by solid vandium oxide
manufacturing of methanol
catalysed by solid chromium oxide
why can transition metals act as catalysts and group 1 metals can’t
they have variable oxidation states
example of homogenous catalyst you must no
peroxodisulfate ions oxsdise iodide ions to iodine
the uncatalyzed reaction has high activation energy as the 2 negative ions repel each other
Fe2+ catalyses it in a 2 step process
S2O8 + 2Fe2+ -> 2SO42- + 2Fe3+
2I- + 2Fe3+ -> I2 + 2Fe2+
both steps then are between positive and negative ions
in the second step the catalyst is regenerated
what is an autocatalyst
a homogeneous catalyst where one of the products of the reaction actually catalyses the reaction as it proceeds further
e.g oxidation of ethanedioic acid and managaate ions
describe the oxidation of ethanedioic acid by magnate ions
the rate starts of slow as there is no catalyst intially
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 catalysed
the rate then decreases and levels off as the reactants get used up
why is the titration of Fe2+ and MnO4 self indicating
as the MnO4- reactants to form Mn2+ it turns from deep purple to colourless
as the MnO4- is added to the Fe2+ solution it decolourises as it reacts
as soon as all the Fe2+ is reacted the reaction mixture will start to turn pale pink as the MnO4- has nothing to react with
purple (MnO4-) + (Fe2+) pale green
goes pink Fe3+ ?
