3.4 D-block

Question 1

What is the D-block?

Answer 1

the set of elements whose highest energy electrons are found in d-orbitals

Question 2

What is a transition element?

Answer 2

a metal that possesses a partially filled d sub-shell in its atom or stable ions

Question 3

Why is zinc classified as a d-block but not a transition metal?

Answer 3

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

Question 4

Which two elements do not obey the rules for filling orbitals?

Answer 4

Chromium and Copper.

Question 5

What are the electron configurations of chromium and copper and why are they this way?

Answer 5

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.

Question 6

What happens in terms of removing electrons when transition metals are ionised?

Answer 6

4s electrons are lost first before 3d as this is more energetically favourable as 4s and 3d are close together in energy

Question 7

What does the oxidation state favoured by each metal depend on?

Answer 7

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

Question 8

What is a ligand?

Answer 8

a small molecule that can form a bond to a transition metal e.g. H2O, NH3, Cl-, CN-

Question 9

Why can ligands form bonds in this way?

Answer 9

They are electron rich molecules and have lone pair so these can form coordinate bonds with the empty orbitals on the transition metal ions.

Question 10

What is the combination of a transition metal ion with its ligands called?

Answer 10

a complex

most ion are actually complexes with water molecules as ligands around the transition metal ion

Question 11

How are ligands written?

Answer 11

3d shapes. Most are octahedral (bond angle 90) or tetraheldral (bond angle 109.5). Must be drawn with wedged and dashed lines.

Question 12

What colour is [Fe(H20)6]2+

There are 6 water molecule ligands here

Answer 12

pale green complex

Question 13

What colour is [Fe(H20)6]3+

Answer 13

yellow complex

Question 14

What colour is [Cu(H20)6]2+

Answer 14

blue complex

Question 15

What colour is [Cr(H20)6]3+

Answer 15

dark green complex

Question 16

What colour is [Co(H20)6]2+

Answer 16

pink complex

Question 17

what are two examples of tetrahedral complexes and their colours?

Answer 17

[CuCl4]2- is a yellow or green complex
[CoCl4]2- is a blue complex

Question 18

What are the three complexes of copper which can be used to demonstrate variation in transition metal complexes?

Answer 18

[Cu(H2O)6]2+, [Cu(NH3)4(H20)2]2+
[CuCl4]2-

Question 19

What are the two complexes of colbalt which can be used to demonstrate variation in transition metal complexes?

Answer 19

[Co(H2O)6]2+ and [CoCl4]2-

Question 19

Similarities between [CoCl4]2- and [CuCl4]2-

Answer 19

• 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

Question 20

Similarities between [Co(H2O)6]2+ and [Cu(H2O)6]2+?

Answer 20

• 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)

Question 21

How do you form [Cu(NH3)4(H20)2]2+?

Answer 21

Addition of ammonia to [Cu(H2O)6]2+ causes 4 ammonia molecules to replace water molecules forming a royal blue solution

Question 21

What is the arrangement of [Cu(NH3)4(H20)2]2+?

Answer 21

Octrahedral. But two different arrangments. Trans isomer (water molecules opposite pole= more common), Cis isomer (water molecules next to each other)

Question 22

How is Le Chateliers principle related to this topic?

Answer 22

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

Question 23

Whats the important thing to remember about transition metal atoms?

Answer 23

They are only coloured in complexes

Question 24

What causes complexes to be coloured?

Answer 24

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.

Question 24

Why are some complexes colourless?

Answer 24

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

Question 25

Where is iron used in industry?

Answer 25

The Harber process, to produce ammonia from nitrogen and hydrogen (catalyst)

Heterogenous catalysis

Question 26

Where is nickle used in industry?

Answer 26

Hydrogenation of vegetable oils to form margarine (catalyst)

Heterogenous catalysis

Question 27

What transition metal compound is the catalyst for the contact process that produces sulfuric acid?

Answer 27

Vanadium (V) Oxide

Heterogenous catalysis

Question 28

What transition metal compound is the catalyst for the decomposition of hydrogen peroxide?

Answer 28

Maganese dioxide MnO2

Heterogenous catalysis

Question 29

Why can transition metals act as catalysts?

Answer 29

empty orbitals and variable oxidation states mean they can act as intermediaries and provide an alternative lower energy route for the reaction

Question 30

How is having empty orbitals a useful property of a catalyst?

Answer 30

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

Question 31

How is having variable oxidation states a useful property of a catalyst?

Answer 31

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

Question 32

How do homogenous catalysts usually work?

Answer 32

they form coordinate bonds with the reactants then use their variable oxidation states to oxidise/reduce them which makes the reactant more reactive

Question 33

Why are metal ion complexes often acidic?

Answer 33

They occur as hydrated complexes with a high positive charge density, this means they can readily loose H+

Question 34

How to form a metal hydroxide?

Answer 34

Add alkali to a positively charged metal complex, forms insoluable metal hydroxide and water

Question 35

What are the observations of adding Sodium Hydroxide to solutions containing complexes?

Answer 35

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