13.1 Coloured complexes Flashcards
list out the key properties of the transition metals
- a high melting point, boiling point and density
- act as catalysts in reactions
- exhibits temporary magnetism in response to external magnetic fields
- they all have +2 oxidation states
- all form coloured complexes
- all form complex ions
define paramagnetism
strong and results from alignment of unpaired electrons
- paramagnetic atoms are attracted to a magnet
define diamagnetic
weak and results from alignment of paired electrons
- diamagnetic atoms are repelled by magnets
what are complex ions?
structures composed of a transition metal ion surrounded by ligands
held in place by dative covalent bonds
define dative covalent bonds
form of covalent bond where both electrons are donated by a single atom
define ligand
species with a spare pair of electrons, known as a lone pair, that forms dative covalent bonds with a central ion
what are the 2 types of ligands?
- monodentate; one lone pair, e.g. h2o and nh3
- polydentate; more than one lone pair, e.g. nh2ch2ch2nh2
what’s a coordination number?
number of lone pairs bonded to the transition metal ion
what are the oxidation states for water and ammonium ligands?
neutral, 0
what are the oxidation states for halides, hydroxides and cyanide ligands?
-1
how does coloured complexes form?
when a transition metal is surrounded by ligands in a complex ion, there is a repulsion between the d-orbital electrons and the ligands lone pair
why are transition metals coloured?
- d-d orbitals splits
- partially filled d subshells (d1 - d9)
explain the d-d transition phenomenon where complex ions absorbs light
- visible light promotes an electron from a lower energy d-orbital to a higher energy d-orbital
- complex ions appears complementary in colour to the light that is absorbed
what are the 2 main factors that affect the colour of the complex ion
- identity of the metal
- nature of the ligand
what does it mean if the nature of ligands is further to the right or further to the left? (series can be found in section 15)
further to the right: the bigger the split for the ligands
further to the left: the smaller/ lower the split
what does more splitting mean in terms of light frequency?
the more splitting there are, the higher frequency of light that is absorbed
whats the colour of [Cu(H2O)6]^2+?
blue
whats the colour of [Cu(NH3)4(H2O)2]^2+?
deep blue
whats the colour of [Fe(SCN)(H2O)5]^2+?
blood red
what is the colour of [Ni(H2O)6]^2+?
green
during the addition of ammonia to aqueous copper sulphate, a ligand swap occurs with water, what observations would be expected?
- given that ammonia is higher on the spectrochemical series
- higher energy light will be absorbed
- such as blue
- therefore the solution will change to the complementary colour of orange
define isoelectronic
having the same numbers of electrons or the same electronic structure
explain why [Ti(H2O)6]3+, and other complex ions alike, display colours (3)
- ligands cause splitting of the 3d orbital into 2 energy levels
- energy from visible light promotes an electron from a lower energy level to a igher energy level
- the energy absorbed is in the visible regioin of the spectrum
- so the complementary colour is expressed
concentrated ammonia was added to [Ti(H2O)6]3+ in a solution. How would this impact the wavelength of light absorbed by the solution? (2)
- as the ammonia is concentrated, it would displace/ replace the H2O ligands with NH3 ligands
- NH3 is further up the electrochemical series than H2O
- therefore, higher energy light is absorbed with a lower wavelength
