Transition Metals Part 1 Flashcards
Transition metal
A metal that can form one or more stable ions with an incomplete d sub shell
Why are Sc and Zn d block elements
Because their outer electron is in a (3)d sub shell
Why are Sc and Zn not transition metals
They don’t form a stable ion with in incomplete d sub shell
What are the four characteristic properties of transition metals
Form coloured compounds
Variable oxidation state
Catalysts
Form complex ions
What do the characteristic properties of transition metals arise due to
Incomplete d sub shell
Complex ion
Central metal ion surrounded by ligands
Ligands
A molecule/ion that forms a coordinate bond with a transition metal by donating a pair of electrons
3 types of ligands
Monodentate, bidentate and multidentate
Monodentate ligands
Molecules/ions that can donate one electron pair to the central mental ion to form one coordinate bond
Bidentate ligands
Molecules/ions that can donate 2 electron pairs to the central metal ion to form 2 coordinate bonds
Multidentate ligands
Molecules or ions that can donate more than 2 electron pairs to the central mental ion to form more than 2 coordinate bonds
Coordination number
The number of coordinate bonds to the central metal atom/ion
What is coordination number not necessarily the same as
The number of ligands
When is coordination number the same as number of ligands
In monodentate ligands
What are the two common shapes of complex ions
Octahedral and tetrahedral
What 2 other shapes are also sometimes complex ions
Square planar and linear
Why do complexes containing water and/or ammonia ligands usually have an octahedral shape
Because they usually have a coordination number of 6
Why do complexes containing chloride ligands usually have a tetrahedral shape
They usually have a coordination number of 4
Why do complexes of copper and silver usually have a linear shape
They usually have a coordination number of two
What are ligand substitution reactions
Reaction where one ligand is replaced by another
Why does the coordination number and shape not chance when a ligand substitution reaction occurs between NH3 And H2O
They are similar in size
equation for aqueous cobalt salts reacting with excess ammonia (all 6 water ligands replaceed)
[Co(H2O)6]2+ +6NH3 >< [Co(nh3)6]2+ +6H2O
colouur change when aqueous cobalt II salts react with excess ammonia
pink to pale brown
equation for aqueous copper II salts reacting with excess ammonia (4 water ligands replaced)
[Cu(H2O)6]2+ + 4NH3 >< [Cu(H2O)2(NH3)4]2+ +4H2O
colour change when aqueous copper II salts are reacted with excess ammonia
pale blue to dark blue
coordination number and shape for aqueous copper II salts reacting with excess ammonia (4 water ligands replaced)
6-6
octabhedral- octahedral
why do reactions involving chloride ligands involve a change in coordination number AND SHAPE
chloride ligand larger than NH3 and H2O
equation aqueous cobalt II salts reacted with conc hcl (all 4 ligands replaced)
[Co(H2O)6]2+ + 4Cl- >< [CoCl4]2- + 6H2O
COLOUR, COORD NUMBER AND SHAPE aqueous cobalt II salts reacted with conc hcl (all 4 ligands replaced)
colour: pink-blue
coord no- 6 to 4
shape: octahedral to tetrahedrial
haemoglobin: coordination number of iron II in haem unit
4
haemoglobin: shape around iron II i haem unit
square planar
haemoglobin: what does planar haem unit bound to and what does it bind to in body
complex protein called globin
both water and oxygen can bind to iron II as ligands
haemoglobin: what happens inthe lungs as a result of the concentration of oxygen being high
equilibrium shifts right and water ligands are substituted for oxygen molecules to form haemoglobin
haemoglobin: which is the process of water/oxygen binding to haemoglobin reversed
when oxyhaemoglobin gets to where it is needed
haemoglobin: what is the coordination number around iron in oxyhaemoglobin
6
haemoglobin: what can haemoglobin substitute H2O ligands for when carbo monoxide is inhaled
Co
haemoglobin: why is carbon monoxide considered toxic
bond between carbon monoxide and iron II is very strong and not readily revewrsed
preventsw oxygen being bonded to haemoglobin
why are enthalpy changes usually quite small in ligand substitution reactions
often little change in number and types of bond present
What happens when reactions occur that substitute bidentate and multidentate ligands for monodentate ligands
Complex formed often very stable and reaction hard to reverse
When is a reaction feasible in terms of energy
If free energy, delta G, is negative
What does delta G equal
Delta H - T delta S
Why is there a large increase in entropy of a reaction when there is an increase in moles
Disorder is increased
Chelate effect
Multidentate and bidentate ligands replace monodentate ligands to form complexes
Why are transition metal ions coloured
Because they have an incomplete d sub shell
What do all the d orbitals in a transition metal atom have exactly the same
Energy
Why do complex ions have some orbitals with more energy than other
Interactions between ligands and electrons in d orbitals gives some more energy than others
What does how the orbitals split depend on
The coordination number of the complex
What are electrons promoted from and to when visible light is absorbed
Electrons promoted from lower energy (ground state) to higher energy (excited state)
When transition metal ions absorb visible light corresponding to a colour this colour is…
Missing from the spectrum
Why is the complementary colour to the one hat is absorbed seen
The remaining colours are transmitted
What does the frequency of light absorbed depend on
The size of the energy gap
Delta E equals
hv
What is h
Plancks constant = 6.63x10-34 Js
V equals (definition )
Frequency of light absorbed
V equals
c/ŷ
C equals
Speed of light = 3x10^8
Ŷ equals
Wavelength of light
what factors induce change of colour in reaction
- change in coordination number
- change in ligand
- change in oxidation state
why does change in coordination number induce colour change
splitting in the dorbitals is different in octahedral complexes than tetrahedral so when coordination number changes from 6 to 4 colour will also change
example colour change due to change in coordination number equation
[Co(H2O)6]2+ + 4Cl- >< [CoCl4]2- + 6H2O
colour change [Co(H2O)6]2+ to [CoCl4]2-
pink to blue
what is a change in coordination number always accompanied by
a change in ligand
why does a change in ligand induce a colour change
different ligands have different effects on the energies of d orbitals so when ligand changes the size of deltaE changes and hence the colour changes
example nickel ligand changing from H2O to NH3
[Ni(H2O)6]2+ + 6NH3 >< [Ni(NH3)6]2+ + 6H2O
colour change when nickel ligand changes from water to ammonia
green to blue
why does a change in oxidation state induce a colour change
as oxidation state of metal increases so does size of energy gap, delta E. this leads to a change in colour
example of irons ox state changing 2+ to 3+
[Fe(H2O)6]2+ > [Fe(H2O)6]3+
what is spectrometry the study of
how electromagnetic radiation interacts with matter
what is colorimetry a type of
spectroscopy
what does a colorimeter measure and what does it give a measure of
measures amount of light absorbed by a solution and gives a measure of colour intensity
what you must first do to find the concentration of an unknown
generate a calibration curve
colourimetry experiment
- create 4/5 standard solutions of known concentrations
- select filter of complimentary colour and measure absorbance of known solutions
- unknowns absorbance can be measured and conc found from calibration curve
why must 4/5 standard solutions be made in colorimetry
to provide enough data to draw a line of best fit with confidence
why must a filter be used in colorimetry
to select out the complementary colour, this is the light the sample absorbs
stereoisomerism
compounds with the same structural formula but a different arrangement of atoms in space
what type of complexes can exhibit stereoisomerism
square planar and octahedral
when can cis-trans isomers form in square planar complexes
when it has 2 different ligands
formula of cisplatin
[Pt(NH3)2Cl2]
when can octahedral complexes exhibit cis-trans isomerism
2 different ligands- 4 of one and 2 of another
which complexes can exhibit optical isomers
octahedral complexes containing bidentate ligands
optical isomers
non superimposable mirror images
Examples of complexes that exhibit optical isomerism
[Ni(en)3]2+ and [Co(C2O4)3]3-
