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23 - Transition Metals Flashcards

1
Q

What are the properties of transition metals? (8)

A

Good conductors of heat and electricity
Hard and strong
Shiny
High m.p and b.p
Not very reactive
Malleable and ductile
Good catalysts
variable oxidation states

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2
Q

What are the two exceptions when looking at the electron configurations of the transition metals?

A

Cr
Cu`

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3
Q

Why does chromium only have 1 electron in the 4s orbital?

A

The half-filled 3d orbital is more stable.

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4
Q

Why does copper only have 1 electron in the 4s orbital?

A

The full 3d orbital is more stable.

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5
Q

What is a d-block element?

A

An element with their highest energy electron in the d-orbital.

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6
Q

What is a transition metal?

A

An element that forms one or more table ions, which have an incomplete d-subshell.

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7
Q

Why are Sc and Zn not considered transition metals?

A

Sc forms 3+ ions and Zn forms 2+ ions, where
the d-subshell is not partially full.

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8
Q

Why do transition metals have high melting and boiling points?

A

Stronger metallic bonding - as they can delocalise electrons from both the 3d and 4s orbitals and their cations have a high charge so there is a greater electrostatic attraction. The ions are also small so they pack together well.

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9
Q

What ion does Sc form?

A

3+

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10
Q

What ion does Zn form?

A

2+

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11
Q

What ions does Cr form?

A

3+
6+

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12
Q

What ions does Mn form?

A

2+
7+ (exists as MnO4-)

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13
Q

What ions does Fe form?

A

2+
3+

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14
Q

What ions does Cu form?

A

1+
2+

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15
Q

Why does the stability of the 2+ ion increase across the period?

A

There is an increase in nuclear charge and number of electrons in the d-orbitals.

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16
Q

What is a ligand?

A

An ion or molecule with a lone pair of electrons that forms co-ordinate bonds with a transition metal ion.

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17
Q

What is the co-ordination number?

A

The number of co-ordinate bonds formed between a central metal ion and its ligands.

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18
Q

When are hexaaqua ions formed?

A

When transition metal salts dissolve in water.

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19
Q

How are hexaaqua ions formed? (process)

A

Six water molecules surround the positively charged metal ion and the water acts as a Lewis base and donates their lone pair of electrons to the metal ion.

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20
Q

What shape are hexaaqua ions?

A

Octahedral

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21
Q

What is a monodentate ligand?

A

A ligand that binds to the metal ion using a single lone pair of electrons.

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22
Q

What are examples of monodentate ligands?

A

Water
Ammonia
Chlorine
Cyanide
Hydroxide
Oxide

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23
Q

What are water ligands referred to when naming complex ions?

A

Aqua

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24
Q

What are ammonia ligands referred to when naming complex ions?

A

Ammine

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25
What are chlorine ligands referred to when naming complex ions?
Chloro
26
What are cyanide ligands referred to when naming complex ions?
Cyano
27
What are hydroxide ligands referred to when naming complex ions?
Hydroxo
28
What are oxide ligands referred to when naming complex ions?
Oxo
29
What are examples of bidentate ligands?
Ethane diamine Ethandioate Benzene-1,2-diol
30
What are examples of multidentate ligands?
EDTA Ethylene Diamine Tetra Acetic acid
31
How many co-ordinate bonds can edta form?
6
32
What is a chelate?
A complex compound where the central metal ion is bonded to a multidentate ligand.
33
Why are chelate complexes favoured over complexes with monodentate ligands?
When a multidentate ligand replaces multiple monodentate ligands the entropy increases, as there is an increase in the number of molecules, this favors the formation of the chelate complex.
34
What is HAEM?
A complex with a central iron(ll) ion, which is responsible for the red colour in blood and the transport of oxygen by red blood cells.
35
What shape does a complex with a co-ordination number of 2 form?
Linear
36
What shape does a complex with a co-ordination number of 6 form?
Octahedral
37
What shape does a complex with a co-ordination number of 4 form?
Tetrahedral - weak ligands Square planar - strong ligands
38
What are examples of weak ligands?
H2O Cl-
39
What are examples of strong ligands?
CN- NH3
40
What factors affect the co-ordination number of a complex ion?
Shape and size of ligand - bigger ligand = smaller number Size of metal ion - larger ion = more ligands = greater number Electron configuration and intermolecular interactions.
41
What isomers can the complexes form?
Geometrical Optical
42
What metal complexes can from optical isomers?
If the complex has two or more bidentate ligands.
43
What are optical isomers?
Compounds that are non-superimposable mirror images of eachother.
44
When naming complexes what name is used if the complex is a cation or neutral?
The metal name
45
When naming complexes what name is used if the complex is an anion?
The metal name, ending with -ate.
46
Why are some transition metal complexes colourless?
The ions with an empty or full d-orbital are colourless as all the sub-shells are degenerate so no light is absorbed.
47
What does it mean if sub-shells are degenerate?
All sub-shells are on the same energy level.
48
Why are some transition metal complexes coloured?
In an isolated metal atom all d-orbitals are the same energy level, but in a compound the other atoms make the d-orbitals have different energies. When electrons are promoted to a higher energy level they absorb energy in the visible region of the spectrum, which is proportional to the difference in energy between levels, so the compound appears as a combination of the colours not absorbed.
49
What determines a transition metal complexes colour?
The compound appears as a combination of the colours wavelength that is not absorbed.
50
What is the formula for energy change?
△E = hv △E = frequency x Planck's constant
51
What determines the wavelengths of colours absorbed in transition metal complexes?
Transition metal Oxidation state Ligands attached Co-ordination number
52
What is colorimetry?
A method to measure the concentration of a solution by shining light through a sample and measuring the amount of light transmitted through the solution.
53
How is colorimetry used to find the formula of a complex ion?
Light of a certain wavelength is passed through a solution. The greater the colour intensity the greater the absorbance. The concentration of each species in the complex is altered repeatedly. The mixture with the greatest absorbance identifies the ration of ligands to ions.
54
Why do transition metals have variable oxidation states?
They can use electrons from both their 3d and 4s orbitals in bonding.
55
What reaction happens with most transition metal compound?
Redox
56
What conditions are used to oxidise lower oxidation state ions and why?
Alkaline solution As in alkaline solution there is a tendency to form negative ions, which aids electron loss.
57
How can low oxidation state transition metals be stabilised?
By keeping them in acidic solution
58
What are heterogeneous catalysts?
Catalysts in a different phase to the reactants.
59
How do heterogeneous catalysts work?
Adsorption - The species forms bonds with the catalyst on the active site, using bonding electrons, which weakens it, making the reaction easier. Reaction - The absorbed species is held at the right orientation, increasing the chances of a favourable collision taking place. Desorption - There is a rearrangement of electrons, releasing the product from the active site.
60
How can a heterogeneous catalyst be made more effective?
Finely divide it - increases surface area, providing more collision sites. Spread the catalyst onto an inert support medium, increasing the surface-to-mass ration and reducing cost.
61
What is poisoning?
When impurities in the reaction mixture adsorb onto the catalysts surface, removing active sites for reaction molecules, decreasing efficiency.
62
What transition metals are good when it comes to strength of adsorption on heterogeneous catalysts?
Nickel Platinum
63
What is the Contact process used for?
To produce sulphuric acid.
64
What is the overall reaction for the Contact process?
2SO2 + O2 <--> 2SO3
65
What are the two reaction steps involved in the Contact process?
SO2 + V2O5 -> SO3 + V2O4 2V2O4 + O2 -> 2V2O5
66
What catalyst is used in the Contact process?
V2O5
67
What are homogeneous catalysts?
When the catalyst is in the same phase as the reactants.
68
How do homogeneous catalysts work?
The reaction proceeds through an intermediate species with a lower activation energy.
69
What is the overall reaction for the iodine clock reaction?
(S2O8)2- + 2I- --> 2(SO4)2- + I2
70
What are the two reaction steps involved in the iodine clock reaction?
(S2O8)2- + 2(Fe)2+ + 2(SO4)2- + 2(Fe)3+ 2(Fe)3+ + 2I- -> 2(Fe)2+ + I2
71
What is the catalyst in the iodine clock reaction?
Iron(ll)
72
Why does iron(ll) speed up the iodine clock reaction?
The uncatalysed reaction takes place between two negative ions, which repel each other so there is high activation energy. Whereas both steps of the catalysed reaction involve reaction between oppositely charged ions, so the overall activation energy is lower.
73
What is autocatalysis?
A reaction where one of the products acts as a catalyst.
74
What is an example of an autocatalysed reaction?
2MnO4- + 16H+ + 5(C2O4)2- -> 2Mn2+ + 8H2O + 10CO2 Mn2+ acts as the catalyst.

Chemistry (31 decks)

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