Transition Metals Flashcards
Define Transition Metals
These are d-block elements that can form one or more stable ions with incomplete filled d-orbitals
Why is Zn not a transition metal?
Zn can only form a 2+ ion. In this ion the Zn 2+ has a complete d orbital and so does
not meet the criteria of having an incomplete d orbital in one of its compounds.
Why is Sc not a transition metal?
Sc can only form a +3 ion. In this ion the Sc3+ has an empty d orbital and so
does not meet the criteria of having an incomplete d orbital in one of its ions.
Characteristics of Transition Metals
*complex formation,
*formation of coloured ions,
*variable oxidation state
*catalytic activity.
Manganese is a transition metal. It forms stable manganese(II) ions, Mn2+,
and stable permanganate(VII) ions, MnO4–. With reference to the electronic configurations of these ions, explain why manganese shows variable oxidation numbers.
Manganese has the electronic configuration [Ar] 4s2 3d5 so its outer electrons are in the 4s and 3d subshells. These subshells
are very close in energy [1 mark]
so there is no great difference
between removing electrons from the 4s subshell (e.g. to make Mn2+) or from the 3d subshell (e.g. to make MnO4–) [1 mark].
The energy released when manganese forms compounds or complexes containing manganese in variable oxidation numbers
is greater than the energy required to remove these outer electrons [1 mark], (so manganese can exist with variable oxidation numbers).
Define Complex Ion ?
This is a metal ion surrounded by
dative covalently (coordinately) bonded ligands.
What is the coordination number ?
This is the number of ligands (atoms, ions, or molecules) that are bonded directly to a central metal ion in a coordination complex. It represents the total number of bonds formed between the central metal ion and the ligands surrounding it.
Transition metal ions form a wide range of different colours when bonded to ligands.
Using your knowledge of 3d orbitals, explain how ligands cause transition metals to be coloured.
Normally, all the 3d orbitals have the same energy. When ligands form dative covalent bonds with a metal ion, the 3d electron orbitals split in energy. Electrons tend to occupy the lower orbitals and energy is required to move an electron from an lower 3d orbital to a higher one. The energy needed to make an electron jump from the lower 3d orbital to the higher 3d
orbital is equal to a certain frequency of light. This frequency gets absorbed. All the other frequencies are transmitted and it is these frequencies that give the transition metal colour.
Amphoteric
Can act as an acid or base depending on the condition of the reaction
A student is measuring the rate of the reaction between MnO4– ions and C2
O4^2– over time. She predicts that the rate will decrease with time, but discovers instead that the rate of reaction
over the first five minutes increases. Explain the student’s results with use of appropriate equations.
- The overall equation for the reaction is:
2MnO4(aq) + 16H^+ (aq) + 5C2O42(aq) —-> 2Mn2+ (aq) + 8H2O(l) + 10CO2(g) [1 mark]. - This is slow to begin with, because the MnO4– and C2O42– ions are both negatively charged, so repel each other and don’t collide very frequently [1 mark].
- The Mn2+ product, however, is able to catalyse the reaction. It reduces MnO4– to Mn3+:
MnO4– (aq) + 4Mn2+ (aq) + 8H+ (aq) —–> 5Mn3+ (aq) + 4H2O(l) [1 mark]. - The Mn3+ ions are reduced back to Mn2+ by reaction with C2O4^2–:
2Mn3+(aq) + C2O42– (aq) —–> 2Mn2+(aq) + 2CO2(g) [1 mark]. - This means the reaction is an autocatalysis reaction. As more Mn2+ is produced, there is more catalyst available and so the reaction rate will increase [1mark].
What is adsorption
this is when the reactant molecules are attracted to the surface of the solid catalyst and stick to it
Explain how adsorption helps to catalyse a reaction ?
- The surface of the catalyst activates the molecules, weakening the
bonds between the atoms in the reactants [1 mark] - making them easier to break and reform as the products [1 mark].
