transition metals Flashcards
define transition element
an element which forms at least one stable ion with a partially full d- shell of electrons
characteristic physical properties
metallic good conductors hard strong shiny high mp/bp low reactivity
uses of iron
vehicle bodies
reinforce concrete
uses of titanium
jet engine parts
uses of copper
water pipes
characteristic chemical properties
variable oxidation states
coloured compounds in solution
good catalyst
form complex ions
complex ion
central transition metal ion surrounded by ligands that are coordinated bonded to it
catalysts in processes
iron - haber
vanadium oxide - contact
MnO2 - decomposition of H2O2
which electrons do transition metals lose first when forming ions
4s
define ligand
an ion or molecule with at least one lone pair of electrons, that donates them to a transition metal ion to form a coordinate bond and thus a complex ion
monodentate ligands
cl-
H2O
NH3
Cn-
ethanedioate
.. .. O - O - \ / C -C / / \\ O O
ethane-1,2-diamine
:NH2 - CH2 - CH2 - :NH2
how many coordinate bonds does EDTA4- form
six
define coordination number
the number of coordinate bonds the metal ion has formed to surround the ligand
chelate effect
chelate complexes with multidentate ligands are favoured over monodentate ligands or ligands that form fewer coordinate bonds per molecule
chelate effect in terms of entropy
number of molecules increases when multidentate ligands , displace ligands that form fewer coordinate bonds per molecule
more stable complex ion formed
transition metal in water
Aqua ion, 6H2O ligands
octahedral
transition metal with two ligands
linear
transition metal with four ligands
tetrahedral
platin
square planar
conditions needed for a complex ion to display optical isomerism
octahedral with two or more bidentate ligands
haem
a molecule which makes up protein chains, with an Fe2+ central metal ion
coordination number = 6
4 of which bonds to porphyrin, 1 to nitrogen of a globin protein, 1 to oxygen
haemoglobin transport oxygen
O2 forms weak coordinate bond to the metal ion which is transported around the body. the bond breaks when haemoglobin reaches cells
why is CO toxic
coordinately bonds to FE2+ and is a better ligand so bonds more strongly than O2
stops O2 from bonding so it can not be transported around the body
why are transition metal compounds coloured
partially filled d orbitals
in compounds with ligands the d orbital splits into different energy levels
energy gap
see reflected light
delta E
\
hf= hc/ /\
how is delta E changed
oxidation state of metal
number/type of ligands
shape
coordination number
VO2^+
VO^2 +
V^3+
V^2+
5+ yellow
4+ blue
3+ green
2+ violet
what reduces vanadium
zinc
what colour is Fe2+ aqua ion
green
what colour is Fe3+ aqua ion
pale brown
what colour is Cr2+ aqua ion
blue
what colour is Cr3+ aqua ion
red/violet
what colour is Co2+ aqua ion
brown
what colour is Co3+ aqua ion
yellow
what does a colorimeter do
measure the absorbance of a particular wavelength of light by a solution
which oxidation states do all transition metals have except Sc
2+
colour of MnO4^-
deep purple
colour of MN2+
pink
reduction of MnO4^-
MnO4^- + 8H+ +5e- = Mn2+ + 4H2O
colour of Cr2O7^2-
orange
colour of Cr3+
green
reduction of Cr2O72-
Cr2O72- + 14H+ + 6e- = 2Cr3+ + 7H2O
what happens to aqua metal ions in acidic conditions
they get reduced
what happens to aqua metal ions in alkaline conditions
they get oxidised
define a catalyst
a substance that increases the rate of a reaction without being chemically changed at the end of the reaction
how do catalysts usually work
provide an alternative reaction pathway with a lower activation energy
why are transition metals good catalysts
they can exist in variable oxidation states so can provide alternative pathways easily
advantages of using a catalyst
allows reactions to proceed at lower temperatures and pressures
metals used in catalytic converters
Pt
Rd
Pd
heterogeneous catalyst
catalyst is in a different phase to the reactants
activity occurs on the solid surface as the reactants pass over it
heterogenous catalysts work
reactants absorb the catalyst’s surface at active sites. this weakens bonds within the reactants, holds reactants close together on the surface and/or in the correct orientation to react. once the reaction has occurred, products desorb from active sites
what is catalyst poisoning
unwanted impurities adsorb to the catalyst’s active sites and do not desorb
this blocks the active sites
how can a catalyst be degraded
finely divided catalyst can be gradually lost from their support medium
Haber process
N2 + 3H2 = 2NH3
iron catalyst
contact process
SO2 + V2O5 = SO3 + V2O4
V2O4 + 1/2O2 = V2O5
homogenous catalyst
catalyst that is in the same phase as the reactants
form intermediates to give a different reaction pathway with a lower activation energy
