24) Transition elements Flashcards
For which two elements does the expected principle of electrons filling singly in orbitals before pairing does not apply?
Chromium (3d5 4s1) and Copper (3d10 4s1)
the 1/2 full or fully filled 3d sub-shell to give additional stability
Define transition element
a d-block element which forms an ion with an incomplete d-sub-shell
(not Sc -> Sc3+ or Zn -> Zn2+)
Give 3 features of transition elements
- form compounds in which the transition element has different oxidation states
- form coloured compounds
- the element and their compounds can act as catalysts e.g. vanadium (V) oxide in the Contact process - production of sulfur dioxide
What is a species containing a transition element in its highest oxidation state often?
a strong oxidising agent
Define complex ion
a transitional metal ion bonded to ligands by coordinate (dative covalent) bonds
When is a complex ion formed?
when 1 or more molecules / anions (ligands) bond to a central metal ion
Define ligand
a molecule or ion that can donate a pair of e- to the transitional metal ion
Define coordinate bond
a shared pair of e- in which the bonded pair has been provided by one of the bonding atoms only
Define coordination number
the total number of coordinate bonds formed between a central metal ion and ligands
What is the overall charge of a complex ion?
the sum of the charges on the central metal ion and any ligands present
Describe the written formula of a complex ion e.g. [Cr(H2O)6]3+
square brackets used to group all of the parts of the complex ion together
ligand inside round brackets
overall charge of complex outside square brackets
Define monodentate ligand
a ligand that is able to donate 1 pair of e- to a central metal ion
Give 5 examples of monodentate ligands
H2O: \:NH3 \:Cl- cyanide, :CN- \:OH-
Define bidentate ligand
a ligand that can donate two lone pairs f e- to the central metal ion, forming two coordinate bonds
Give 2 examples of bidentate ligand
1,2-diaminoethane ethanedioate ion (oxalate ion)
What does the shape of a complex ion depend upon?
its coordination number
Six-coordinate complexes can form which shape?
octahedral
Four-coordinate complexes can form which 2 shapes?
tetrahedral
square planar
In which complex ions does a square planar shape occur?
in those of transition metals with 8
Describe cis-trans isomerism in octahedral complexes with monodentate ligands
4 of 1 type of ligand and two of another type of ligand
Describe optical isomerism in octahedral complexes
contain 2 or more bidentate ligands
‘cis’ isomers only
What are trans-isomers of octahedral complexes unable to show optical isomerism?
mirror image is exactly the same and can be superimposed
Describe the role of cis-platin in cancer treatment?
forms a platinum complex inside of a cell which binds to DNA, preventing DNA replication
activation of the cell’s own repair mechanism leads to apoptosis
Define ligand substitution
a reaction in which one or more ligands in a complex ion are replaced by different ligands
What colour is [Cu(H2O)6]2+ as a solution?
pale blue
What happens to [Cu(H2O)6]2+ upon small addition of NH3?
Cu(OH)2, copper (II) hydroxide forms
pale blue ppt
What colour is [Cu(H2O)6]2+ as a solution?
pale blue
What happens to [Cu(H2O)6]2+ upon small addition of NH3?
Cu(OH)2, copper (II) hydroxide forms
pale blue ppt
What happens to [Cu(H2O)6]2+ in excess of NH3?
[Cu(NH3)4(H2O)2]2+
dark blue solution
4 ammonia ligands replace 4 of the water ligands
What happens to [Cu(H2O)6]2+ upon small addition of NH3?
Cu(OH)2, copper (II) hydroxide forms
pale blue ppt
What colour is [Cr(H2O)6]3+ as a solution?
violet
What happens to [Cr(H2O)6]3+ upon small addition of NH3?
Cr(OH)3, chromium (III) hydroxide
grey-green ppt
What happens to [Cr(H2O)6]3+ in excess of NH3?
[Cr(NH3)6]3+
dark purple solution
What happens to [Cr(H2O)6]3+ in excess of NH3?
[Cr(NH3)6]3+
dark purple solution
What colour is chromium (III) sulfate dissolved in water?
[Cr(H2O)5 SO4]+
green solution
What happens to [Cu(H2O)6]2+ in conc. HCl?
[CuCl4]2-
yellow solution (if not carried out to completion intermediate = green)
tetrahedral shape
6 water ligands have been replaced by 4 chlorine ligands
chlorine ligands are larger in size so fewer can fit around the central Cu 2+ ion
Describe ligand substitution with relation to haemoglobin
CO can bind by ligand substitution to form carboxyhaemoglobin (irreversible)
if CO conc is too high, transport of O2 is prevented - leading to death
Define precipitation reaction
the formation of a solid from a solution during a chemical reaction
When are precipitates often formed?
when two aqueous solutions are mixed together
What happens to Cu 2+ on the small addition of OH- ?
Cu(OH)2
pale blue ppt
What happens to Cu 2+ on the small addition of OH- ?
Cu(OH)2
pale blue solution -> pale blue ppt
What happens to Cr 3+ on the small addition of OH- ?
Cr(OH)3
violet solution -> grey-green ppt
What happens to Fe 2+ on the small addition of OH- ?
Fe(OH)2
iron (II) hydroxide
pale green solution -> green ppt
What happens to Fe 3+ on the small addition of OH- ?
Fe(OH)3
iron (III) hydroxide
yellow/orange solution -> orange-brown ppt
What happens to Mn 2+ on the small addition of OH- ?
Mn(OH)2
manganese (II) hydroxide
pale pink solution -> light brown ppt
What happens to Cr 3+ upon an excess of OH- ?
[Cr(OH)6]3-
dark green solution
What is significant about the reactions of Fe2+, Fe3+ and Mn2+ with aqueous ammonia?
they react in the same way as with aqueous sodium hydroxide, forming precipitates
Standard electrode potentials can be used to explain _. The more positive the E⦵ value, the more likely equilibrium is to _ electrons, shift to the _ and undergo _.
redox reactions
gain
RHS
reduction
Suggest why vanadium does not form ions in which vanadium has an oxidation state greater than +5?
only 5 e- in 4s and 3d sub-shells
