23 Tranistion Metals Flashcards
Definition of transition metal element
The formal definition of a transition element is that it is one that forms at least one stable ion with a path full d-shell of electrons. Scandium only forms Sc3+ (3d0) and zinc only forms Zn2+ (3d10). ( they are d block elements but not transition metals)
Chemical properties of transition metals
Variable oxidation states - have more than one oxidation state
Colour - different coloured ions
Catalysis - affects the rate of reaction without being used up
Complex formation - transition elements form complex ions
Co-ordination number
The number of ligand molecules bonded to a metal ion
Ligand
An atom, ion or molecule that forms a co-ordinate (dative) bond with a transition metal ion using a lone pair of electrons
Example of ligands
H2O:
:NH3
:Cl-
:CN-
Aqua ions
If you dissolve the salt of a transition metal in water
Copper sulphate = the positive charged metal ions becomes surrounded by water molecules acting as ligands
Multidentate ligands
More than one atom with a lone pair of electrons which can bond to a transition metal ion
Bidentate ligands
Ethane 1,2 diamine
Ethanedioate (oxalate) ion
Benzene -1,2- diol
Chelate effect
Add a hexadentate ligand such as EDTA to a solution of a transition metal salt
[Cu(H2O)6]2+ + EDTA4- —— [CuEDTA]2- +6H2O
Haemoglobin
Red pigment in blood
Responsible for carrying oxygen from the lungs to the cells of the body
Fe2+
Tranistion metals
Electrons are being added to the d-sub-level
Good conductor of heat and electricity
Hard , strong ,high melting and boiling point
Low chemical reactivity
co-ordination number
number of co-ordinate bonds to ligands that surround the d-block metal ion
Aquas ions
dissolve the salt of a transition metal in water, the positively charged metal ion becomes surrounded by water molecules acting as ligands
Ethane-1,2-diamine
each nitrogen had a lone pair which can forms a co-ordinate bond to the metal ion
EDTA
this can act as a hexadentate ligand using Loeb pairs on four oxygen and both nitrogen atoms. complex ions with polydentate ligands are called chelates. Chelates can be used to effectively removed d-block metal ions from solution
chelate effect
enhanced affinity of chelating ligands for a metal ion compared to the affinity of a collection of similar nonchelating ligands for the same metal.
Haemoglobin
red pigment
carries oxygen form the lungs
four of the co-ordination sites are taken up by a ring system called a porphyrin which acts as a tetra dentate ligand.
anaemia
shortage of haemoglobin
body suffers from a lack of oxygen
metal compounds are coloured
coloured is caused by the compounds absorbing energy that corresponds to light in the visible region of the spectrum.
why are transition metal complexes coloured
transition metal compounds are coloured because they have part filled d-orbitals
electrons can move between d-orbitals
E = hv = hc/λ
frequency of light is related to the energy difference
frequency is related to the colour of light. violent is of high energy and therefore high frequency and red is low energy and low frequency
colour of transition metal complex depends on the energy gap which depends on the oxidation number and also on the ligands.
Colorimetry
a simple colorimeter uses a light source and a sector to measure the amount of light of a particular wavelength that passes through a coloured solution. the more concentrated the solution, the less light transmitted through the solution. a colorimeter is used with a suitable calibration graph to measure the concentration of solutions of coloured transition metal compounds.
redox titrations
find out how much acid is required to react with certain volume of base
Fe2+ reacts with potassium manganate int he ratio 5:1
using a burette, you gradually add potassium manganate solution to solution containing Fe2+ ions acidified with excess dilute sulphuric acid. the purple colour disappers as the MnO4- ions are converted to pale pink Mn2+ ions to leave a virtually colourless solution.
oxidation of transition metal ions in alkaline solutions
high oxidation state of a mental are reduced in acidic solution. oxidation of lower oxidation states of transition metal ions tends to happen in alkaline solution