12 An introduction to the chemistry of transition elements Flashcards
The complex ion [Cr(H2O)6] 3+ can be converted into [CrCl 2(H2O)4] +.
(i) Suggest a suitable reagent for this conversion.
Ref: 9701/42/O/N/16
Concentrated HCl or any soluble chloride ion
In an isolated transition metal atom the five d orbitals have the same energy. When a transition metal ion forms a tetrahedral complex the d orbitals are split into two groups of different energies.
Complete an orbital energy diagram to show this, indicating the number of orbitals in each group.
Ref: 9701/42/F/M/16
2 groups of non degenerate orbitals
3 over 2
Platinum(II) forms a four co-ordinate complex containing two ammonia molecules and two chloride ions.
This complex exists as two isomers.
One of the isomers in (ii) is an important anticancer drug. State which isomer this is and explain why this isomer is effective.
Ref: 9701/42/F/M/16
Cis isomer because it can react and bond with DNA. This prevents the recplication of the strand/ cell division.
State the colours you would observe when concentrated HCl(aq) is added to an aqueous solution of cobalt(II) nitrate, Co(NO3)2.
Give the formulae and geometry of the complexes formed.
Ref: 9701/41/M/J/16
solution starts pink
turns blue
pink is [Co(H2O)6]2+
blue is [CoCl4]2–
this complex is tetrahedral
[Cu(H2O)6] 2+ + 4Cl – [CuCl 4] 2– + 6H2O
State the colours of these two complex ions.
[Cu(H2O)6] 2+
[CuCl 4] 2– [1]
Cu(H2O)6]2+ blue
and
[CuCl4] 2– yellow OR yellow/ green OR green / yellow
[Cu(H2O)6] 2+ + 2NH3 [Cu(NH3)2(H2O)4] 2+ + 2H2O equilibrium 1
[Cu(H2O)6] 2+ + en [Cu(en)(H2O)4] 2+ + 2H2O equilibrium 2
What do these Kstab values tell us about the relative positions of equilibria 1 and 2?
equilibrium 2 lies more to the RHS/ favours forward reaction more
Nickel forms the complex ion [Ni(en)3] 2+ in which it is surrounded octahedrally by six nitrogen atoms.
Name the type of stereoisomerism displayed by [Ni(en)3] 2+
Draw three-dimensional diagrams to show the two stereoisomers of [Ni(en)3] 2+.
Ref: 9701/41/O/N/16
optical
The following scheme shows some reactions of [Co(H2O)6] 2+.
Explain why compounds of transition elements are usually coloured.
Ref: 9701/42/O/N/16
d orbitals split into lower and upper orbitals
light /photon absorbed
electron(s) promoted / excited / jumps up to (higher) (d–) orbital
or
electron(s) moves / jumps (from lower (d–)) to higher (d–) orbital
Draw the shape of one of the d orbitals.
Ref: 9701/42/F/M/17
Complete the diagram to show how the presence of ligands around an isolated transition metal ion affects the energy of the d orbitals.
Ref: 9701/42/F/M/17
[Cu(H2O)6] 2+ is pale blue but [Cu(NH3)4(H2O)2] 2+ is deep purple-blue. Suggest a reason for this.
Ref: 9701/42/F/M/17
different frequency /wavelength of light are absorbed by the two complexes OR different size of energy gap
Describe and explain the differences in the density and the melting point between cobalt (a transition element) and calcium ( a group 2 element)
- Cobalt has a higher density than calcium because it has a higher Ar and a smaller atomic radius
- Cobalt has a higher melting point than calcium because there are stronger electrostatic forces of attraction between the ion and the electrons as more electrons are released.
Explain what is meant by structural isomer in the context of transition elements.
molecules that have the same number and type of atoms but a different structural formula.
Explain what is meant by stability constant.
It is the equilibrium constant for the formation of a complex ion in a solvent from its constituent molecules.
