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Chemistry Unit 3 > ✅3.4: D Block Transition Elements > Flashcards

✅3.4: D Block Transition Elements Flashcards

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1
Q

Define the d-block

A

The d-block is the groups of elements whose outer electrons are found in the d-orbitals

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2
Q

Define a transition element

A

A transition element is a metal that possesses a partially filled d sub shell in its atom or stable ions

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3
Q

What elements does the d block contain in the first row?

A

Consists of elements from scandium to zinc, with the Ar of 21 (Sc) to 30 (Zn)

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4
Q

Name some shared characteristics of the first row d block elements

A

Elements are hard, dense materials with generally high melting points

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5
Q

What elements in the first row of the d block are also transition elements? Why?

A

Elements from scandium (Sc) to nickel (Ni) as they have partially filled d-orbitals in the unreacted metals.
Copper is also a transition metal despite having a full set of d-orbitals as a metal because it has partially filled d-orbitals in most of its compounds

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6
Q

Why is Zinc not considered a transition metal

A

Zinc has a filled d sub-shell in a zinc atom and maintains this in its compounds, as the d sub shell is never partially filled it’s not a transition element

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7
Q

What is important to remember when filling in electrons in boxes after argon

A

The order of filling orbitals for these elements is: 4s, 3d then 4p.

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8
Q

What two transition elements are exceptions to the rules on filling electrons in box’s

A

1) Chromium (Cr)

2) Copper (Cu)

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9
Q

Give the atomic number and electron configuration of Chromium (Cr)

A

Atomic number= 24
Electronic configuration=
2 2 6 2 6 5 1
1s 2s 2p 3s 3p 3d 4s

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10
Q

Give the atomic number and electron configuration of Copper (Cu)

A

Atomic number = 29
Electronic configuration:
2 2 6 2 6 10 1
1s 2s 2p 3s 3p 3d 4s

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11
Q

Why do copper and chromium not follow the electron configuration rules?

A

Due to the similar energy of the 3d and 4s sub shells, it does not take much to move electrons between them and so factors such as repulsion between between electrons in the same sub-shell and pairing energy for electrons in the same orbital are enough to change the stable electronic configuration

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12
Q

Key note to remember the electronic configuration of copper and chromium

A

Shells are more stable if they are filled or half filled

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13
Q

What is filled before what (in terms of electronic configuration)
What is removed before what (in terms of electronic configuration)

A

The 4s sub shell is filled before the 3d sub shell

The 4s electrons are lost before the 3d electrons

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14
Q

Why are the 4s electrons removed before the 3d electrons

A

The 4s and 3d orbitals are very close together in energy, so it is more energetically favourable to lose these 4s electrons before the 3d electrons.

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15
Q

What is the common oxidation states of Cr? (2)

A

Cr3+ and Cr6+

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16
Q

What is the common oxidation states for Mn (5)

A

+2, +3, +4, +6 and +7

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17
Q

What are the common oxidation states for Fe (2)

A

+2 and +3

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18
Q

What are the common oxidation states for Co? (2)

A

+2 and +3

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19
Q

What are the common oxidation states for Cu? (2)

A

+1 and +2

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20
Q

Why can transition metals form different oxidation states?

A

The energies of the 4s and 3d orbitals are similar and so the energy required to remove any of these electrons is similar

As the elements form compounds energy is readily released (either through forming covalent bonds or an ionic lattice) so the energy needed to reach higher oxidation states and the energy released in compound formation is finely balanced allowing a range of oxidation states to form

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21
Q

What is the main factor determining the common oxidation states of transition metals?

A

The oxidising power of the atoms in the compound. For instance chlorine gas is a sting oxidising agent and :: form iron (lll) chloride, whereas iodine vapour is a far weaker oxidising agent and so can only oxidise to form iron (ll) iodide.

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22
Q

How big are transition metal ions?

What charge do transition metals have?

A

Transition metal ions are small

They can have large positive charges

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23
Q

Define the term ligand

A

A small molecule with a lone pair that can form a bond to a transition metal (normally a co-ordinate bond)

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24
Q

Give some examples of common Ligands

A

H20, NH3, Cl-, CN-

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25
Q

Define the term complex

A

A combination of the transition metal ion and a ligand

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26
Q

Briefly describe the 3 stages in forming a complex

A

1) A Metal (M) has an empty orbital, and the ligand has a lone pair of electrons
2) The two atomic orbitals overlap to form a molecular orbital
3) A co-ordinate bond is formed between the transition metal ion and the ligand

27
Q

What is the most common arrangement of a transition metal complex?

A

6 ligands arranged octahedrally around the metal atom.
Bond angle = 90

      B

B B

       A

B B

        B
28
Q

What is the least common arrangement of a transition metal complex?

A

4 ligands arranged tetrahedrally around the metal atom, bond angle = 109.5 degrees

                B
                 I
                 I
     109.5  A 
               /   \ 
             /       \      B
          B           B
29
Q

Give some examples of octahedral transition metal complex’s + state their colours
What hint should you remember?

A

[Fe(H2O)6]2+ = pale green complex

[Fe(H2O)6]3+ = yellow complex

[Cu(H2O)6]2+ = blue complex

[Cr(H2O)6]3+ = dark green complex

[Co(H2O)6]2+ = pink complex

Hint: always a positive 2+/3+ charge
(H2O)6 shows it’s octahedral

30
Q

Give some examples of tetrahedral transition metal complex’s + state their colours
What hint should you remember?

A

[CuCl4]2- =yellow or green complex

[CoCl4]2- = blue complex

Hint: always negative 2- charge
[xxxx4] shows it’s tetrahedral

31
Q

What is the colour of the compounds (Fe2+, Fe3+, Cu2+, Cr3+) if there are no specified ligands

What is different about Co2+ in the absence of ligand (water)

A

They are all colourless in the absence of the ligand H2O

Co2+ is blue in the absence of water

32
Q

What is the order of the lines in the octahedral transition metal complex structure?

A 
Stating from the top: 
Solid 
Dashed 
Black wedge 
Solid 
(Look at diagram pg 44)
33
Q

What are the 3 known transition metal complex’s of copper, what can they be used to show?

A
  1. [Cu(H2O)6]2+
  2. [Cu(NH3)4(H2O)2]2+
  3. [CuCl4]2-
34
Q

[Cu(NH3)4(H2O)2]2+

What is important to note about the copper transition metal complex shown above?

A

It has 2 isomers, both with an octahedral straight, dashed, black wedge, straight arrangement.
One has H20 at either pole, opposite each other (trans isomer) the most common arrangement whereas one has its H2O either both on the RHS or both on the LHS (cis isomer)

35
Q

What colour is [Cu(NH3)4(H2O)2]2+ solution?

A

Royal blue solution.

36
Q

Why is there two different isomers of [Cu(NH3)4(H2O)2]2+

A

Because it contains two different ligands there are two different arrangements of these ligands

37
Q

Where does the bonding occur in the octahedral transition metal complex
[Cu(H2O)6]2+

A

One lone pair of each oxygen atom of the water molecules is used to form a co-ordinate bond to the Cu metal ion

38
Q

When are [CuCl4]2- and [CoCl4]2- complex’s formed?

A

Formed when copper (II) or cobalt (II) ions react with concentrated HCL, which displaced the water molecules.

39
Q

Name the colour changes of the transition metal ions Cu(II) and Co(II) when reacted with HCL

A

Cu(II) goes from pale blue to yellow/green

Cobalt(II) goes from pink to blue

40
Q

Explain why the colour attributed to [CuCl4]2- or [CoCl4]2- varies?

A

The ligand-complex equilibria are often simplifications as many different complex’s are formed when we have mixed ligands me hense when a complex is formed [CuCl4]2- or [CoCl4]2- is only one component in a complex mixture.

41
Q

What happens when a transition metal ion is exposed to a mixture of ligands?

What kind of reaction is this and how can we tell what the products are?

A

When it’s exposed to a mixture of ligands (e.g aqueous solution containing chloride ions) ligands can exchange rise form a new complex.
This is an equilibrium process, and hence the concentrations of the metal ions and possible ligands are key to identifying the species in the solution present

42
Q

Give an example where the equilibrium between complexes can lead to a change in geometry depending on the ligands used.

A

Equation:
[Co(H2O)6]2+ + 4Cl- —> [CoCl4]2- + 6H2O

According to Le Chatelier’s principle, if you added more concentrated HCL the equilibrium would shift to the RHS forming tetrahedral transition metal complex [CoCl4]2-, whereas it’s you added extra H2O the equilibrium would shift to the LHS producing the octahedral [Co(H2O)6]2+ transition metal ligand.

43
Q

What is important to note about the colours of transition metal ion?

A

They are only coloured (excluding Co2+) in complexes, in the absence of ligands around the metal ion they are colourless

44
Q

What does a transition metal atom have without the presence of ligands?

A

It has 5 degenerate d orbitals (5d orbitals with the same energy)

45
Q

Where do the first 3 d orbitals point?

A

They point between a pair of axis

46
Q

Where do the last 2 d orbitals point?

A

They point along a pair of axes,

The first along the x and y axis and the second along the z axis

47
Q

What happens to make the d orbitals or a transition metal atom non degenerate? (have different energy)

A

Example: in an octahedral complex

  • 6 negatively charged ligands approach the transition metal ion along the three axis (x,y,z)
  • negative charges repel the electrons In the orbitals that point along these axis (last 2 d orbitals) making them less stable
  • the first 3 orbitals are not made less stable
  • the energies of the d orbitals are no longer the same splitting the d orbital into 2 distinct energy groups
48
Q

In an octahedral complex which group of split d orbitals has more energy?

A

The last 2 d orbitals that point across the axis have more energy than the first 3d orbitals that point between the axis

49
Q

Describe how an electron can move from the lower energy state d orbital to the higher energy state d orbital after interacting with a ligand, what physical effect does this have on the complex?!

A

The electrons in the lower energy d of orbital absorbs energy form light, which corresponds to the energy gap between orbital, the relationship is given by the equation E=hf.
The light that remains gives the complex its characteristic colour.

50
Q

Why do different transition metal complex’s transmit different colours when ligands split their d orbitals?

A

The amount of splitting of d-d transitions varies between ions of different transition metal complex’s.
As the splitting varies so does the frequency (colour of light absorbed) leading to different colours for different complex’s.

E.g for [Cu(H2O)6]2+ the colour blue is transmitted as the electrons absorbs all frequencies of light to be promoted to the higher energy state apart from blue.

51
Q

Why are Cu+ and Zn2+ compounds colourless?

A

These complexes have a full d sub-shell (d10) which means there are no empty orbitals to allow electrons to move between energy levels.
:: these complexes don’t absorb light in the visible spectrum and appear colourless.

52
Q

Define the term catalyst

A

A substance which increase the rate of a chemical reaction by providing an alternative pathway with a lower activation energy

53
Q

Define the term homogeneous catalyst

A

Catalysts that are in the same physical state as the reactions they catalyse

54
Q

Define the term heterogeneous catalyst

A

Catalysts that are in a different physical state from the reactions that they catalyse

55
Q

What is a main use for transition metals in industry.

A

They are used as catalysts

56
Q

Give 3 examples where the transition metal itself is used in chemical processes as a catalyst

A

1) Iron: harbour process: to produce ammonia from nitrogen and hydrogen
2) Nickel: hydrogenation of vegetable oils to form margarine
3) Platinum: oxidation if ammonia to form nitric acid

57
Q

Give 2 examples where transition metal compounds are used as a catalyst in chemical processes:

A

1) Vanadium Oxide (V2O5): Contact process: production of sulfuric acid
2) Manganese dioxide (Mn02): catalytic decomposition of hydrogen peroxide

58
Q

Name some general uses for transition metal catalysts vital to our current economy:

A

Needed to make almost all plastics, artificial fibres, fertilisers, explosives, ethanoic acid and most other acids and solvents including ethanal.

59
Q

Give 2 reasons why transition metals ions make good catalysts

A

1) they have partially filled d orbitals

2) they have variable oxidation states

60
Q

Explain why transition metals having partially filled 2 orbitals allows them to be a good catalyst

A
  • they Have enough empty orbitals to combine with other molecules
  • Molecules with the lone pairs conform coordinate bonds to the metal atom to phone complexes and this can increase the reactivity of the species bonded to the metal, or bring two reacting molecules closer together
  • this makes a reaction more likely especially when the solid surface can provide an area where molecules are absorbed and brought close together for a reaction
61
Q

Explain why transition metals having variable oxidation states allows them to be a good catalyst

A
  • The variable oxidation states allow the metal ion to act as a catalyst in redox reactions
  • it can act as an oxidising agent or reducing agent by oxidising or reducing one of the reactants
  • the transition metal can then be returned to its original oxidation state by reaction with another molecule appearing unchanged at the end of the reaction.
62
Q

In what way are heterogenous catalysts good catalyst

A

They are typically solids that provide a surface for molecules to be absorbed and come together in an advantageous arrangement

63
Q

In what way are homogenous catalysts good catalysts

A

They use the variable oxidation states oxidised/reduce a reactant which makes it more reactive

64
Q

We’re all examples of catalysts listed as examples (5 of them) heterogeneous or homogenous? What does this mean?

A

Iron, nickel, platinum, vanadium oxide and manganese dioxide are all heterogeneous catalysts.
This means that absorption is a key stage in the alternative reaction route they provide.

Chemistry Unit 3 (6 decks)

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