transition metals Flashcards
what is a transition element?
an element which forms a stable ion which has a partially filled d sub shell
what is a d block element?
an element which has its electrons in its d sub shell
which d block elements aren’t transition metals and why?
scandium - has no electrons in its d sub shell when it forms an ion
zinc - has a full d sub shell when it forms an ion
out of the 4s and 3d sub shell, which one fills up first?
4s
what is the electron configuration of a chromium ion?
[Ar] 4s1 3p5
what is the electron configuration of copper?
[Ar} 4s1 3d10
give some of the properties of transition elements?
forms coloured ions
acts as a catalyst
has variable oxidation states
can form complexes
what’s a complex?
a molecule with a transition metal ion in the centre with ligands coordinately bonded to them
what is a ligand?
an atom or a molecule that donates a pair of electrons to a central metal ion to form a coordinate bond
what is the coordination number?
the number of coordinate bonds formed to a central metal ion
what is a monodentate ligand?
atoms or molecules which only form one coordinate bond to the complex ion
give some examples of monodentate ligands
Cl-, NH3, H2O, OH- and CN-
what are bidentate ligands?
molecules which have two atoms which each have a lone pair of electrons which can each form a coordinate bond to a central metal ion
give an example of a bidentate ligand
ethane-1,2-diamine - H2NCH2CH2NH2
C2O4^2-
what are multidentate ligands?
ligands which can form more than one coordinate bond to a central metal ion because they have multiple atoms with lone pairs available to form coordinate bonds
give an example of a multidentate ligand
EDTA
how many coordinate bonds does EDTA form?
6
what is a ligand substitution reaction?
a reaction where one ligand which is coordinately bonded to a central metal ion is replaced by another ligand
when does a ligand substitution reaction with no change in coordination number occur?
when small and uncharged ligands are used
what is haem?
an iron(II) complex with a multidentate ligand
how does haemoglobin carry oxygen?
Oxygen forms a co-ordinate bond to Fe(II) in haemoglobin, enabling oxygen to be transported in the blood.
why is carbon monoxide toxic?
replaces oxygen, co-ordinately bonded to Fe(II) in haemoglobin so oxygen can’t be carried
what is the chelate effect?
when bidentate and multidentate ligands replace monodentate ligands in a complex
what is the link between coordination number and the enthalpy change?
no change in coordination number = no enthalpy change
more coordinate bonds broken than made means an increase in enthalpy
what determines the entropy change of a ligand substitution reaction?
the number of reacting particles and the number of product particles
what is the shape of a complex with 6 coordinate bonds joined to it?
octahedral
what is the bond angle in octahedral complexes?
90
which octahedral complexes form E-Z isomers?
Those in the form of ML4A2 (all monodentate)
which octahedral complexes can form optical isomers?
Those formed from bidentate ligands
what is the bond angle in tetrahedral complexes?
109.5
give some examples of tetrahedral complexes
[CuCl4}2-
[CoCl4]2-
[FeCl4]-
what is cisplatin
an ant-cancer drug
what kind of isomerism does cisplatin show?
E-Z isomerism
in what form is cisplatin active?
the Z form
how does cisplatin work?
forms bonds between the bases in DNA so it stops DNA replication in tumour cells and stops tumours from growing
what is the bond angle in square planar complexes?
90
what happens to the d sub shell when a complex is formed?
it’s split into two different orbitals at two different energy levels
how are transition metal complexes coloured?
when they’re hit by light, light is absorbed and promotes electrons from ground state to excited state
some light is absorbed
colour arises when other wavelengths are transmitted
what does the colour of a complex depend on?
shape of the complex
ligands attached to it
coordination number
metal ions and different charges
what formula can you use to calculate energy difference between orbitals?
delta E = hv = hc/v
h = Planck constant c = speed of light v = frequency Hz
give an example of a linear compound
[Ag(NH3)2]+
what is colorimetry?
the measurement of colour intensity using a colorimeter
how does a colorimeter work?
light shone through a sample and absorbance calculated
filter used to get a specific wavelength of light
absorbance compared against a calibration curve
when do you use a spectrophotometer?
when the compound is colourless so colorimetry can’t be used as the compound doesnt absorb visible light but does absorb UV light
how can vanadium be reduced?
by a reducing agent such as zinc in the presence of an acid
describe the colour change as vanadium goes from +5 to +2
yellow —> blue —> green —> violet
what is tollen’s reagent used for?
testing for the presence of aldehydes and ketones
what is potassium manganate used for?
titrations - testing how many moles of acid and alkali there are
what is a homogenous catalyst?
a catalyst which is in the same physical state as the reactants
what is a heterogenous catalyst?
a catalyst which is in a different phase to the reactants
explain how catalysts work
by chemisorption
- reactants are adsorbed onto the active site on the surface of the catalyst
- reactant bonds weakened
- held in a more favourable shape
- product molecules leave the catalyst’s surface
how can catalysts be poisoned?
a substrate binds irreversibly to the active site so they have a reduced efficiency
what are the implications of catalyst poisoning?
have to be replaced which is expensive
how can catalyst poisoning be reduced?
purify reactants before reacting them
what is autocatalysis?
when the product in a reaction acts as a catalyst for the reaction
why is the reaction of manganate ions and ethanedioate ions slow at first?
both negatively charged so they repel each other because of the high activation energy
why does the rate of reaction increase as manganate and ethanedioate ions react?
because Mn^2+ is formed which catalyses the reaction
why can manganese and iron act as catalysts?
they have variable oxidation states
what is the test for 3+ ions?
adding sodium carbonate and seeing if there’s effervescence
why are 3+ ions more acidic?
higher charge
draw electrons in more (away from H)
H is a better leaving group
complex therefore acts as an acid
what colour is potassium mangante in acid?
colourless
what colour is potasium manganate in alkali?
purple
name an example of homogenous catalysis?
S2O8^2- and I-
give an example of autocatalysis?
MnO4- and C2O4^2-
why is the reaction of MnO4- and C2O4^2- slow at first?
ions repel each other
high activation energy
small amount of catalyst at first
