3.4 D-block Flashcards
What is the D-block?
the set of elements whose highest energy electrons are found in d-orbitals
What is a transition element?
a metal that possesses a partially filled d sub-shell in its atom or stable ions
Why is zinc classified as a d-block but not a transition metal?
It has a filled D sub shell and maintains this in its compounds. As its D-subshell is never partially filled it is not a transition element
Which two elements do not obey the rules for filling orbitals?
Chromium and Copper.
What are the electron configurations of chromium and copper and why are they this way?
See book for configuration. The small energy difference between 3D and 4S orbitals and the extra energy required to pair electrons means that these configurations are more stable than the alternatives.
What happens in terms of removing electrons when transition metals are ionised?
4s electrons are lost first before 3d as this is more energetically favourable as 4s and 3d are close together in energy
What does the oxidation state favoured by each metal depend on?
oxidising power of other atoms in a compound. E.g. chlorine can oxidise iron to iron(iii) chloride but iodine cannot oxidise iron to the 3+ oxidation state
What is a ligand?
a small molecule that can form a bond to a transition metal e.g. H2O, NH3, Cl-, CN-
Why can ligands form bonds in this way?
They are electron rich molecules and have lone pair so these can form coordinate bonds with the empty orbitals on the transition metal ions.
What is the combination of a transition metal ion with its ligands called?
a complex
most ion are actually complexes with water molecules as ligands around the transition metal ion
How are ligands written?
3d shapes. Most are octahedral (bond angle 90) or tetraheldral (bond angle 109.5). Must be drawn with wedged and dashed lines.
What colour is [Fe(H20)6]2+
There are 6 water molecule ligands here
pale green complex
What colour is [Fe(H20)6]3+
yellow complex
What colour is [Cu(H20)6]2+
blue complex
What colour is [Cr(H20)6]3+
dark green complex
What colour is [Co(H20)6]2+
pink complex
what are two examples of tetrahedral complexes and their colours?
[CuCl4]2- is a yellow or green complex
[CoCl4]2- is a blue complex
What are the three complexes of copper which can be used to demonstrate variation in transition metal complexes?
[Cu(H2O)6]2+, [Cu(NH3)4(H20)2]2+
[CuCl4]2-
What are the two complexes of colbalt which can be used to demonstrate variation in transition metal complexes?
[Co(H2O)6]2+ and [CoCl4]2-
Similarities between [CoCl4]2- and [CuCl4]2-
- Tetrahedral with 109.5 bond angles
- complexes are formed with copper (II) or colbalt (II) ions react with concetrated HCl which displaces water molecules. There are distinct colour changes as the change in ligands and coordination geomertry both contribute to changes in light absorbed
- copper goes blue to yellow/green
- Colbalt goes pink to blue
Similarities between [Co(H2O)6]2+ and [Cu(H2O)6]2+?
- octrahedral
- one lone pair from each oxygen atom of the water molecules used for bonding to the metal ion
- gives familiar colours (Pink for colbalt, blue for copper)
How do you form [Cu(NH3)4(H20)2]2+?
Addition of ammonia to [Cu(H2O)6]2+ causes 4 ammonia molecules to replace water molecules forming a royal blue solution
What is the arrangement of [Cu(NH3)4(H20)2]2+?
Octrahedral. But two different arrangments. Trans isomer (water molecules opposite pole= more common), Cis isomer (water molecules next to each other)
How is Le Chateliers principle related to this topic?
when a transition metal ion is exposed to a mixture of ligands, ligands can be exchanged to form a new complex and this is an equilibrium process. Kc can be found for any exchange. If Kc is large the complex is more stable than the free ions and ligands
Whats the important thing to remember about transition metal atoms?
They are only coloured in complexes
What causes complexes to be coloured?
Splitting in D-orbitals mean electrons can gain energy (absorbed in the form of light) to move from the lower to the upper of these sets of orbitals.
Why are some complexes colourless?
they have an electronic configuration with a full d sub-shell (D10) so there are no empty orbitals to allow electrons to move between energy levels.
Also note ions such as Sc3+ ions have an empty D sub-shell so there are no electrons to move between orbitals
Where is iron used in industry?
The Harber process, to produce ammonia from nitrogen and hydrogen (catalyst)
Heterogenous catalysis
Where is nickle used in industry?
Hydrogenation of vegetable oils to form margarine (catalyst)
Heterogenous catalysis
What transition metal compound is the catalyst for the contact process that produces sulfuric acid?
Vanadium (V) Oxide
Heterogenous catalysis
What transition metal compound is the catalyst for the decomposition of hydrogen peroxide?
Maganese dioxide MnO2
Heterogenous catalysis
Why can transition metals act as catalysts?
empty orbitals and variable oxidation states mean they can act as intermediaries and provide an alternative lower energy route for the reaction
How is having empty orbitals a useful property of a catalyst?
Molecules with lone pairs can form coordinate bonds to the metal atom to form complexes, this can increase the reactivity of the species bonded to the metal or bring two reacting molecules closer together
How is having variable oxidation states a useful property of a catalyst?
It can act as an oxidising or reducing agent by oxidising or reducing one of the reactants. It can then be returned to its original oxidation state by reaction with another molecule
How do homogenous catalysts usually work?
they form coordinate bonds with the reactants then use their variable oxidation states to oxidise/reduce them which makes the reactant more reactive
Why are metal ion complexes often acidic?
They occur as hydrated complexes with a high positive charge density, this means they can readily loose H+
How to form a metal hydroxide?
Add alkali to a positively charged metal complex, forms insoluable metal hydroxide and water
What are the observations of adding Sodium Hydroxide to solutions containing complexes?
https://www.savemyexams.com/a-level/chemistry/edexcel/17/revision-notes/6-advanced-inorganic-chemistry-a-level-only/6-3-reactions-of-transition-metal-elements/6-3-3-reactions-of-ions-in-aqueous-solution/
