DM ghl: D-block electronic configurations; transition metal catalysis Flashcards

1
Q

Indicate the orbital blocks on the periodic table.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Draw a diagram showing the energies of electron sub-shells from n = 1 to n = 4.

State the elements for which this diagram is correct.

A

Correct up to Ni in period 4, after which 4s sub-shell has higher energy than 3d.

Note: energy gaps should decrease with increasing principal quantum numbers, as below.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What defines d-block elements?

A

Elements for which the last-placed electron is in a d-orbital.

Not outermost shell; 4s already filled since lower energy.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the electronic configuration of argon?

A

1s22s22p63s23p6

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Give the electronic configuration of all of the elements in period 4 of the d-block, in terms of the electronic configuration of argon.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Give the electronic configuration of chromium, and explain why it is is not [Ar]3d44s2, as might be expected.

A

[Ar]3d54s1.

This is an energetically favourable arrangement since it avoids repulsion of two electrons in 4s orbital.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Give the electronic configuration of copper, and explain why it is is not [Ar]3d94s2, as might be expected.

A

[Ar]3d104s1

This is an energetically favourable arrangement, since 2 electrons in the fifth 3d orbital experience less repulsion than 2 electrons in the 4s orbital.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Draw a diagram showing the arrangement of electrons in the ground state of elements in the first row of the d-block.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is a transition metal?

A

A d-block element which forms one or more stable ions with incompletely filled d-orbitals.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

From where are electrons first lost when transition metals form simple ions?

A

The 4s sub-shell (and then the 3d sub-shell).

When empty, 3d has more energy than 4s, but this reverses when electrons are populated (quantum physics…)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Which elements are transition metals?

A

Ti to Cu (not Sc or Zn).

All trans metals are d-block elements but not all d-block elements are trans metals.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Use the electronic configurations of the common ions of zinc and scandium to demonstrate why they are not transition metals.

A
  • Zn [Ar] 3d104s2 →* Zn2+ [Ar] 3d10
  • Sc [Ar] 3d14s2 →* Sc3+ [Ar]

Neither form stable ions with incompletely filled d-orbitals, so they are not transition metals.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Why do transition metals exist in variable oxidation states?

A

There are several stable arrangements of their 3d and 4s electrons.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q
  • What are the common oxidation states of iron?
  • Write their electronic configurations.
A

Fe [Ar] 3d64s2

Oxidation state = +2: Fe(II) or Fe2+ [Ar] 3d6

Oxidation state = +3: Fe(III) or Fe3+ [Ar] 3d5

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

With reference to electronic configuration, suggest and explain why Fe(II) is spontaneously oxidised to Fe(III).

A
  • Fe2+ has 2 electrons in its 5th d-orbital, causing repulsion
  • Fe3+ has only one electron in each d-orbital, so experiences less repulsion
  • Fe3+ has the more energetically favourable configuration so is stabler
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q
  • What are the common oxidation states of copper?
  • Write their electronic configurations.
A

Cu [Ar] 3d104s1

Oxidation state = +1: Cu(I) or Cu+ [Ar] 3d10

Oxidation state = +2: Cu(II) or Cu2+ [Ar] 3d9

17
Q

What is the full electronic configuration of vanadium(III)?

A

V [Ar] 3d34s2

V3+ 1s22s22p63s23p63d2

18
Q

Why do the transition metals tend to have higher oxidation states only in combination with other elements?

A
  • Higher oxidation states mean removal of more electrons
  • Makes ions smaller + more charged
  • High charge density
  • More reactive
  • More likely to occur in molecules
19
Q

Suggest why manganese(II) is more stable than manganese(III).

A

Mn2+ [Ar] 3d5

Mn3+ [Ar] 3d4

3d5 electronic arrangement is more stable than 3d4

20
Q
A

C

21
Q

What is a catalyst?

A

A chemical which increases the rate of a reaction by providing an alternative pathway with a lower activation enthalpy, but remains chemically unchanged.

22
Q

What is heterogeneous catalysis?

A

Catalysis in which the catalyst and reactants are in different physical states.

23
Q

What is homogeneous catalysis?

A

Catalysis in which the catalyst and reactants are in the same physical state.

24
Q

Why are 3d transition metals good:

  • Heterogeneous catalysts?
  • Homogeneous catalysts?
A

Heterogeneous: They have 3d + 4s electrons available to form weak bonds with reactants by adsorption.

Homogeneous: They exist in variable oxidation states, since there are several stable arrangements of their 4s + 3d electrons. This allows them to undergo redox.

25
Q

Describe the typical action of transition metals as heterogeneous catalysts.

A
  • Gaseous/liquid reactant(s) are adsorbed onto solid metal surface by forming weak bonds with its 3d + 4s electrons
  • Weakens + breaks bonds in reactants
  • New bonds form
  • Weak bonds break; products are released
26
Q

How does homogeneous catalysis usually occur for transition metal catalysts?

A
  • Aqueous phase
  • Metal ion + reactant(s) → intermediate → product(s)
27
Q
  1. Write an overall equation for the reactions below.
  2. Suggest what is acting as a catalyst, and justify your suggestion.
  3. How could this hypothesis be tested?
A
  1. S2O82-(aq) + 2I-(aq) → 2SO42-(aq) + I2(aq)
  2. Fe2+ since it is reformed (it is a reactant and final product)
  3. Attempt reaction with and without Fe2+ present. If reaction is slower or does not occur without Fe2+, it acts as a catalyst.

You could record initial [Fe2+], then measure final [Fe2+] by manganate(VII) titration. If [Fe2+] were unchanged, you’d have proved it isn’t used up, but not that it’s involved in the reaction.

28
Q

An example of homogeneous catalysis is the reaction between 2,3-dihydroxybutanedioate ions and hydrogen peroxide, catalysed by Co(II) ions, which are pink in aqueous solution.

The reactant mixture begins pink, then turns green and back to pink. Suggest why.

A
  • Mixture initially contains Co2+, which is pink
  • Co2+ reduces H2O2 and is oxidised to intermediate containing Co3+, which is green
  • Co2+ is reformed in products, so pink is seen again
29
Q

An example of homogeneous catalysis is the exothermic reaction between 2,3-dihydroxybutanedioate ions and hydrogen peroxide, catalysed by Co(II) ions.

Draw an enthalpy profile, showing both the uncatalysed and catalysed reaction.

A