definition of a transition metal
form at least one stable ion with an incompletely filled d-sublevel
general e- configuration of a TM
[Ar] 4s^x 3d^y
which sublevel fills and empties first in a TM: 4s or 3d?
4s fills and empties before 3d
is Fe2+ or 3+ more stable and why?
Fe3+
orbitals are occupied singly, so is more stable
in 2+, there is one set of paired e- (draw e- in boxes to show), so there is decreased stability
what is the e- configuration of Cr and why?
[Ar]4s1 3d5
a 4s e- moves to 3d, reduces repulsion as all orbitals are now singly occupied
what is the e- configuration of Cu and why?
[Ar]4s1 3d10
a 4s e- moves to 3d, the completely filled d-sublevel is more stable
four characteristic chemical properties of TM
- variable oxidation states
- catalysts
- forms complexes
- coloured compounds
what does variable oxidation states mean?
the element can form more than one ion
why are TM good heterogeneous catalysts?
use 4s & 3d e- to adsorb reactants
why are TM good homogeneous catalysts?
they can form intermediates, have variable oxidation states so can be oxidised &/or reduced easily
examples of TM heterogeneous catalysts
- Fe in haber process
- Ni or Pt in hydrogenation of alkenes
- Pt/Pd/Rh in catalytic converters
- MnO2 in decomposition of H2O2 (pag 9)
what is a complex?
a central TM ion surrounded by ligands
what is a ligand?
a species which donates lone pairs to a TM ion to form dative bonds (AKA co-ordinate bonds)
what is the co-ordination number?
the number of dative bonds a complex has
what are the possible co-ordination numbers?
2,4,6
what is a monodentate ligand?
a ligand that forms one dative bond
give the formula for a complex
[TM ion (ligand 1)no. (ligand 2)no.]^overall charge
what is a ligand substitution reaction?
a reaction where one type of ligand is swapped for another
what two reasons might a ligand sub rxn occur?
- new complex is more stable
- there has been an increase in entropy
give a half equation for the formation of hydroxide ions
what type of equation is this?
2H2O + O2 + 4e- –> 4OH-
reduction
what are the two 3D shapes possible with coordination number of 4?
bond angles?
tetrahedral (more common) - 109.5
square planar (rare) - 90
how would chemists dissolve one bolt in sulfuric acid and make up the solution to 1dm3?
- dissolve bolt in warm sulfuric acid
- transfer to 1dm3 volumetric flask, make up to the mark
what is the shape and bond angle for coordination number 6?
octahedral - 90
why are coloured compounds formed with ligands?
(long - write down)
when there are no ligands present all 5 d-orbitals have the same energy
when ligands are present the d-orbitals split into 2 sets (set of 2 with higher energy and 3 with lower energy)
visible light of the correct frequency can be absorbed and used to promote electrons from a low energy d-orbital to a high energy d-orbital
the complementary colour is transmitted
