Transition Metals Model Answers
State what is meant by the term ligand
A molecule or ion that bonds to a transition metal ion via a coordinate bond
How is the bond formed between a metal ion and a ligand in a complex ion?
- A lone pair of electrons
- Is donated from the ligand to the metal ion
- Forming a coordinate bond
Explain what is meant by the term bidentate
A ligand that forms two coordinate bonds with the metal ion
Define the term coordination number
The number of bonds formed with the central metal ion in a complex ion.
Explain why the chloride ions in the complex [Co(NH3)6]Cl3 are not considered to be acting as
ligands
They are not bonded by coordinate bonding to the metal ion.
Explain why the Zn2+ ion is not considered to be a transition metal ion
It has a full 3d subshell but transition metals must have an ion that has a partially full 3d subshell.
Explain the meaning of the term complex in terms of bonding
Transition metal bonded to one ore more ligands by coordinate bonding.
Explain why H2 does not act as a ligand
It does not have a lone pair of electrons
Suggest why electron pair repulsion theory cannot be used to predict the shape of complex
ions
There are too many electrons in d subshells
Give two other characteristic properties of transition metals other than formation of
complexes and catalytic action. Give examples of each of these.
- Variable oxidation state -> Fe(II) and Fe(III)
- Characteristic colour of complexes. Cu2+(aq) is blue
Name the potential shapes of transition metal complexes and give examples of each of these.
- Octahedral [Co(NH3)6]2+
- Square planar [Pt(NH3)2Cl2]
- Linear [Ag(NH3)2]+
Explain why equilibrium is displaced to the right in the formation of CaEDTA from Ca(aq).
- There are two moles reactants compared to seven moles of products.
- So the amount of disorder increases
- Therefore the amount of entropy increases
Explain the meaning of the terms ligand and bidentate as applied to transition metal
complexes
- Ligand is an electron pair donor that uses its electron pair to form a coordinate bond
- A bidentate ligand donates two electron pairs from different atoms on the same molecule.
Explain why two complexes have different colours
- The d orbitals will have different energies in different complexes
, - Light is absorbed causing an electron to be excited to a higher energy level
- Different frequencies of light will be absorbed due to the difference in energy gap.
Suggest why the enthalpy change for a ligand substitution reaction is approximately zero
- Bonds formed have a similar enthalpy to the bonds broken
- The same number of bonds is broken as are made.
State the characteristic features of the chemistry of vanadium and its compounds
- Forms coloured ions
- Has variable oxidation states
- Forms complex ions
- Can be used as a catalyst
Explain why complex ions with partially filled d sub levels are usually coloured
- Electrons excited from ground state to an excited state
- Energy for this is absorbed from visible light
Explain why coordinate bonds can be formed between transition metal ions and water
molecules
- Transition metals can accept electron pairs
- Oxygen on water has lone pairs of electrons so it can donate a pair.
State a feature of silver chemistry that is characteristic of the transition elements
- Can form complexes
- Can be used as a catalyst
State a feature of silver chemistry that is not characteristic of the transition elements
- Forms colourless compounds
- Has one common oxidation state
Suggest a method of determining the concentration of a solution, which contains only cobalt
chloride
Colorimetery
Explain why Cu(I) compounds are colourless but Cu(II) compounds are coloured.
- Copper 1 has a fully filled d sub shell
- Copper 2 has a partially filled d sub shell.
Explain what is meant by a multidentate ligand
Many lone pairs form coordinate bonds.
With reference to electrons, explain why aqueous copper(II) ions are blue.
- Electrons are excited to higher energy levels
- Electrons absorb characteristic frequencies that are equal to the energy gap between the two
energy levels
- Blue light is reflected and not absorbed.
Suggest what is done to a heterogeneous catalyst to maximize its efficiency.
- The surface area is increased
- This is done by using a finely divided catalyst
- The catalyst can also be spread on an inert ceramic support
- The catalyst can also be spread on a mesh support.
State what is meant by the term ligand
A molecule or ion that bonds to a transition metal ion via a coordinate bond
How is the bond formed between a metal ion and a ligand in a complex ion?
- A lone pair of electrons
- Is donated from the ligand to the metal ion
- Forming a coordinate bond
Explain what is meant by the term bidentate
A ligand that forms two coordinate bonds with the metal ion
Define the term coordination number
The number of bonds formed with the central metal ion in a complex ion.
Explain why the chloride ions in the complex [Co(NH3)6]Cl3 are not considered to be acting as
ligands
They are not bonded by coordinate bonding to the metal ion.
Explain why the Zn2+ ion is not considered to be a transition metal ion
It has a full 3d subshell but transition metals must have an ion that has a partially full 3d subshell.
Explain the meaning of the term complex in terms of bonding
Transition metal bonded to one ore more ligands by coordinate bonding.
Explain why H2 does not act as a ligand
It does not have a lone pair of electrons
Suggest why electron pair repulsion theory cannot be used to predict the shape of complex
ions
There are too many electrons in d subshells
Give two other characteristic properties of transition metals other than formation of
complexes and catalytic action. Give examples of each of these.
- Variable oxidation state -> Fe(II) and Fe(III)
- Characteristic colour of complexes. Cu2+(aq) is blue
Name the potential shapes of transition metal complexes and give examples of each of these.
- Octahedral [Co(NH3)6]2+
- Square planar [Pt(NH3)2Cl2]
- Linear [Ag(NH3)2]+
Explain why equilibrium is displaced to the right in the formation of CaEDTA from Ca(aq).
- There are two moles reactants compared to seven moles of products.
- So the amount of disorder increases
- Therefore the amount of entropy increases
Explain the meaning of the terms ligand and bidentate as applied to transition metal
complexes
- Ligand is an electron pair donor that uses its electron pair to form a coordinate bond
- A bidentate ligand donates two electron pairs from different atoms on the same molecule.
Explain why two complexes have different colours
- The d orbitals will have different energies in different complexes
, - Light is absorbed causing an electron to be excited to a higher energy level
- Different frequencies of light will be absorbed due to the difference in energy gap.
Suggest why the enthalpy change for a ligand substitution reaction is approximately zero
- Bonds formed have a similar enthalpy to the bonds broken
- The same number of bonds is broken as are made.
State the characteristic features of the chemistry of vanadium and its compounds
- Forms coloured ions
- Has variable oxidation states
- Forms complex ions
- Can be used as a catalyst
Explain why complex ions with partially filled d sub levels are usually coloured
- Electrons excited from ground state to an excited state
- Energy for this is absorbed from visible light
Explain why coordinate bonds can be formed between transition metal ions and water
molecules
- Transition metals can accept electron pairs
- Oxygen on water has lone pairs of electrons so it can donate a pair.
State a feature of silver chemistry that is characteristic of the transition elements
- Can form complexes
- Can be used as a catalyst
State a feature of silver chemistry that is not characteristic of the transition elements
- Forms colourless compounds
- Has one common oxidation state
Suggest a method of determining the concentration of a solution, which contains only cobalt
chloride
Colorimetery
Explain why Cu(I) compounds are colourless but Cu(II) compounds are coloured.
- Copper 1 has a fully filled d sub shell
- Copper 2 has a partially filled d sub shell.
Explain what is meant by a multidentate ligand
Many lone pairs form coordinate bonds.
With reference to electrons, explain why aqueous copper(II) ions are blue.
- Electrons are excited to higher energy levels
- Electrons absorb characteristic frequencies that are equal to the energy gap between the two
energy levels
- Blue light is reflected and not absorbed.
Suggest what is done to a heterogeneous catalyst to maximize its efficiency.
- The surface area is increased
- This is done by using a finely divided catalyst
- The catalyst can also be spread on an inert ceramic support
- The catalyst can also be spread on a mesh support.
