Transition Elements Flashcards
What is meant by the term d-block element?
- element w its highest energy e- in a d-subshell
What is meant by the term transition element?
- a d-block element forming 1 or more stable ions w an partially filled d-subshell
Why are some d-block elements not transition elements?
- bc some elements form only an ion w a full or empty d-sub shells
- e.g. Sc^3+ has an empty d-subshell: 1s22s22p63s23p6
- e.g. Zn^2+ has a full d-subshell: 1s22s22p63s23p63d10
What are the 2 exceptions to the electron configuration?
- Cr: 1s22s22p63s23p63d54s1
- Cu: 1s22s22p63s23p63d104s1
What is metallic bonding?
- the strong electrostatic forces of attraction between positive ions + a sea of delocalised outer e-s arranged in a giant lattice
What are the chemical properties of transition elements?
- variable oxidation states (e.g. iron (II) + iron (III), copper (I) + copper (II))
- compounds form coloured solutions when dissolved in water (e.g. CuSO4 solution is blue + FeSO4 solution is pale green)
- good catalysts (e.g. Iron (II) catalyses Haber process + MnO2 catalyses decomposition of H2O2)
- form complex ions
What is the definition of a complex ion?
- a central transition metal ion bonded to 1 or more ligands by coordinate (dative covalent) bonds
What is the definition of a ligand (Lewis base-electron pair donor)?
- an ion/molecule w a lone pair of e-s that can be donated to a transition metal to form a coordinate (dative covalent) bond
What is the definition of a coordination number?
- total NO° of coordinate (dative covalent) bonds between a central metal ion + its ligands
What is the definition of a monodentate ligand?
- a ligand that donates 1 pair of e-s to central metal ion (e.g. H2O, Cl-, NH3)
What is the definition of a bidentate ligand?
- a ligand donating 2 lone pairs of e-s to central transition metal ion, forming 2 coordinate bonds
What are e.g.s of common bidentate ligands?
- ethane-1,2-diamine (en): H2NCH2CH2NH2
- ethanedioate (ox): C2O4^2-
What is the bond angle in an octahedral, tetrahedral + square planar shaped complex ion?
- octahedral (6 coordination): 90 {e.g. [Cu(H2O)6]2+}
- tetrahedral (4 coordination): 109.5 {e.g. CuCl4^2-}
- square planar (4 coordination): 90 {e.g. Pt(NH3)2Cl2}
What is stereoisomerism?
- compounds w the same molecular + structural formula, but a diff. arrangement of atoms in space
What are examples of complex ions showing cis-trans isomerism + draw them out?
- [NiCl2(NH3)2]
- [Co(NH3)4Cl2]
What are optical isomers?
- isomers that have non-superimposable mirror images so have no line of symmetry {e.g.[Ni(H2NCH2CH2NH2)3]2+}
What is the structure of cis-plantin?
- [Pt(NH3)2(Cl)2]
What is the use of cis-plantin in medicine?
- is an anti cancer drug that binds to nitrogen atoms on bases in DNA in cancer cells
- it undergoes ligand substitution where H2O replaces Cl-
- nitrogen is a better ligand than water so forms coordinate bonds w cis-plantin, distorting shape of DNA + preventing it from replicating = prevents cell division
What is the definition of ligand substitution?
- when 1 ligand in a complex ion is replaced by another ligand in a reaction
What happens when a copper salt (e.g. CuSO4/CuCl2) is dissolved in water?
- it forms the hexaaquo complex [Cu(H2O)6]2+
- the water ligands can then be replaced by other ligands
What forms a pale blue ppt. + write the ionic equation?
- when NaOH/NH3 is added dropwise to Cu2+ ions a pale blue ppt {e.g. Cu(OH)2(H2O)4} forms
- Cu2+ (aq) + 2OH- (aq) —-> Cu(OH)2 (s)
What forms a dark green ppt. + write the ionic equation?
- when NaOH/NH3 is added dropwise to Fe2+ ions a dark green ppt forms
- Fe2+ (aq) + 2OH- (aq) —-> Fe(OH)2 (s)
What forms a rusty brown ppt. + write the ionic equation?
- when NaOH/NH3 is added dropwise to Fe3+ ions a rusty brown ppt forms
- Fe3+ (aq) + 3OH- (aq) —-> Fe(OH)3 (s)
What forms a light brown ppt. + write the ionic equation?
- when NaOH/NH3 is added dropwise to Mn2+ ions a pale brown ppt forms
- Mn2+ (aq) + 2OH- (aq) —-> Mn(OH)2 (s)
What forms a grey-green ppt. + write the ionic equation?
- when NaOH/NH3 is added dropwise to Cr3+ ions a grey-green ppt forms
- Cr3+ (aq) + 3OH- (aq) —-> Cr(OH)3 (s)
What forms a white ppt. + write the ionic equation?
- Cu2+ (blue) can be reduced to Cu+ (white) by the addition of I- causing blue solution to turn red-brown + a white ppt to form
- 2Cu2+ + 4I- —-> 2CuI + I2
How does haemoglobin transport O2 around the body?
- contains haem groups which have a central Fe2+ ion which, O2 acts as a ligand + reversibly binds to
- O2 is carried to respiring cells where it is released
Why is carbon monoxide toxic?
- O2 + CO can both bind to same binding sites of haemoglobin
- O2 ligands can be replaced by CO ligands which bind more strongly + irreversibly, so can’t be removed
- this dec ability of blood to transport O2 around body + carries CO around body instead so tissues are starved of O2
What complex ion forms when excess NH3 is added to [Cu(H2O)6]2+?
- [Cu(NH3)4(H2O)2]2+
- bc only partial ligand substitution occurs
Describe substitution in cobalt (II) complexes.
- the [Co(H2O)6]2+ (aq) complex ion is pink
- when NaOH is added dropwise, partial ligand substitution of 2 H2O ligands by 2 OH- ligands occurs, forming a blue ppt. {Co(OH)2(H2O)4}
- if excess NaOH is added, blue ppt will turn red when warmed
- when HCl is added, complete ligand substitution of H2O ligands by Cl- ligands occurs, causing pink solution to turn blue {[CoCl4]2-}
- adding water to solution causes Cl- to be displaced by H2O so pink solution returns
Describe the disproportionating of copper (I) ions.
- when solid copper (I) oxide, Cu2O, reacts w H2SO4 a brown ppt of Cu(s) + a blue solution of copper (II) sulfate, CuSO4 is formed
- Cu2O(s) + H2SO4(aq) —-> Cu(s) + CuSO4(aq) + H2O(l)
- copper is reduced from +1 in Cu2O to 0 in Cu
- copper is oxidised from +1 in Cu2O to +2 in CuSO4
Describe the reduction of Cu2+ to Cu+.
- a pale blue solution of Cu2+ can be reduced to Cu+ by potassium iodide
- 2Cu2+(aq) + 4I-(aq) —-> 2CuI(s) + I2(aq)
- I- is oxidised to brown I2
- Cu2+ is reduced to Cu+ forming a white ppt
