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A2 CHEMISTRY > Transition Elements > Flashcards

Transition Elements Flashcards

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1
Q

Electron configuration Chromium (24)

A

1s2 2s2 2p6 3s2 3p6 3d5 4s1

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2
Q

Electron configuration Copper (29)

A

1s2 2s2 2p6 3s2 3p6 3d10 4s1

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3
Q

Properties of transition elements

A
  • Coloured compounds
  • Act as a catalyst
  • Form complex ions/Ligand substitution
  • Variable oxidation states
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4
Q

Colour of Co2+ in solution

A

Pink

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5
Q

Colour of Fe2+ in solution

A

Pale green

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6
Q

Colour of Fe3+ in solution

A

Yellow

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7
Q

Colour of Cu2+ in solution

A

Blue

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8
Q

Colour of Co2+ complex hydroxide precipitate and equation

A

Blue which turns beige in the presence of air

+ 2OH- -> (H2O)4(OH)2 + 2H2O

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9
Q

Colour of Fe2+ hydroxide precipitate and equation

A

Green, then turns brick red in presence of O2

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10
Q

Colour of Fe3+ hydroxide precipitate and equation

A

Brick red/ rusty brown

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11
Q

Colour of Cu2+ hydroxide precipitate and equation

A

Blue

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12
Q

What is a bidentate ligand?

A

A ligand which can donate two lone pairs of electrons to the central metal ion to form coordinate bonds

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13
Q

Ligand substitution in complexes:

Cu 2+ and ammonia, first a small amount then in excess

A

A small amount: pale blue precip. of Cu(OH)2

Excess: precip. dissolves, deep blue solution + 4NH3 [Cu(NH3)4(H2O)2]2+ + 4H2O

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14
Q

Cu 2+ and hydrochloric acid

A

Initially turns green then yellow solution

+ 4Cl- equil. [CuCl4]2- + 6H2O

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15
Q

Co 2+ and conc. hydrochloric acid

A

Dark blue solution

+ 4Cl- equil. [CoCl4]2- + 6H2O

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16
Q

Co 2+ and ammonia

A

Small amount: = 2NH3 -> (H2O)4(OH)2 + 2NH4+ green precip

Excess: start from same complex ion, + 6NH3 -> []6NH3 2+ + 6H2O beige then black on standing

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17
Q

What is a transition element?

A

A d block element that forms an ion with an incomplete in d sub-shell.

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18
Q

Why does 4s sub shell fill before 3d sub-shell and which electrons are lost first?

A

Has a lower energy. 4s electrons are lost first

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19
Q

Explanation for unusual electron config.s of chromium and copper

A

More energetically favorable arrangement as lower energy so more stable.

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20
Q

Transition metal uses

A

Nickel alloyed w. copper for making silver coins, titanium in joint replacement parts, iron alloyed for construction

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21
Q

Trend in atomic radii and IE

A

Little variation as electrons are added to inner 3d sub-shell not outer 4s sub-shell which affects atomic radii. Nuclear charge increases but IE doesn’t increase by much due to pretty much same shielding and atomic radii

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22
Q

Why are they denser than s block elements?

A

Smaller ions. Strong bonding between them pulling them close together, greater masses.

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23
Q

Why high melting point?

A

More delocalisable electrons - greater ion charge

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24
Q

Why variable oxidation states?

A

They have a number of electrons with similar ionisation energies.

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25
Q

How act as catalyst?

A

Provide a surface for reaction to take place on. Reactants adsorbed, products desorbed.
Ability to gain or lose electrons means that they can bind to reactants forming an intermediate as part of a chemical pathway with a lower activation energy

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26
Q

Example of transition metals as catalysts

A

Iron metal in haber process
V2O5 in contact process
Nickel in hydrogenation of alkenes
MnO2 in decomp. of hydrogen peroxide

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27
Q

How and why coloured compounds?

A

Need to have partially filled d sub-shells (promote d electrons from lower energy levels to higher energy levels, requiring electrons to be promoted and spaces to promote them into). Colour observed is mixture of wavelengths not absorbed.

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28
Q

What is a complex ion?

A

A transition metal ion bonded to one or more ligands by coordinate bonds

29
Q

What is a coordinate bond?

A

Bond in which both electrons in shared pair are donated by the same bonding atom

30
Q

What is a ligand?

A

A molecule or ion which donates a pair of electrons to the central metal ion to form a coordinate bond

31
Q

What is coordination number?

A

The total number of coordinate bonds formed between a central metal ion and its ligands

32
Q

Why do transition metal ions form complex ions?

A

They are relatively small and have two or more charges, therefore their high charge density makes them strongly polarizing and able to attract lone pairs of electrons or ions on molecules

33
Q

Requirement to act as a ligand

A

At least one lone pair of electrons

34
Q

Formula and charges of following ligands:

  1. Water
  2. Ammonia
  3. Thiocyanate
  4. Cyanide
  5. Chloride
  6. Hydroxide
A
  1. :OH2 & neutral
  2. :NH3 & neutral
  3. :SCN- & -1
  4. :CN- & -1
  5. :Cl- & -1
  6. :OH- & -1
35
Q

What is a monodentate ligand?

A

A ligand that donates just one pair of electrons to the central metal ion to form one coordinate bond

36
Q

Using VSEPR, describe how coordination number influences the shape of complex ions

A

Electron pairs repel each other, coordinate bonds are bonding electron pairs which will repel each other equally and as far apart as possible to minimize repulsion. Thus, number of coordinate bonds will influence the shape of the complex ion

37
Q

What type of complex ions does cis/trans isomerism occur in?

A

Octahedral complex ions that contain four of one type of ligand and two of another
Square planar complex ions

38
Q

Difference between cis and trans complex ion isomers

A

In the cis, the two ligands which are the same are at adjacent corners and 90~ to one another
In the trans, the two ligands which are the same are at opposite corners and 180~ to one another

39
Q

What is a bidentate ligand?

A

A ligand that can donate two lone pairs of electrons to the central metal ion to form two coordinate bonds.

40
Q

What is a hexadentate ligand?

A

A ligand with 6 lone pairs of electrons, each forming a coordinate bond to a metal ion in a complex ion

41
Q

What is EDTA and its usual form in complex ions

A

EDTA 4-:
:N(:O-OCCH2)2 CH2CH2 N:(:O-OCCH2)2
EDTA has Hs attached to O-

42
Q

What does EDTA do?

A

Binds metal ions and decreases the conc. of metal ions in solutions by binding them into a complex (as a chelating agent)

43
Q

Uses of EDTA

A

In detergents, binds to calcium and magnesium to reduce the hardness of water
Uses in some foods as a stabilizer to remove metal ions that might catalyze the oxidation of the product
In medicine, added to blood samples to prevent clotting and used to treat patients with lead and mercury poisoning

44
Q

Which complex ions form optical isomers?

A

Octahedral complexes that contain multidentate ligands

45
Q

Requirements for optical isomers

A

(No plane of symmetry)

  • A complex with three molecules or ions of a bidentate ligand
  • A complex with two molecules or ions of a bidentate ligand, and two molecules or ions of a monodentate ligand
  • A complex with one hexadentate ligand
46
Q

What is a ligand substitution?

A

A reaction in which one ligand in a complex ion is replaced by another ligand

47
Q

Reaction between copper (II) ions and ammonia

A

Small amount of ammonia: ammonia acts as base and blue precipitate of Cu(OH)2 is formed (from blue solution)
When excess ammonia is added, the pale blue precip dissolves and a deep blue solution is formed. Four of water ligands are replaced by ammonias.
[Cu(H2O)6]2+ + 4NH3 [Cu(NH3)4(H2O)2]2+ + 4H2O

48
Q

Reaction between copper (II) ions and conc. HCl

A

Blue solution turns green then yellow. When green, both the blue and yellow, aqua and the chloro complexes are present.
[Cu(H2O)6]2+ + 4Cl- [CuCl4]2- + 6H2O

49
Q

Cobalt (II) ions and conc. HCl

A

Pale pink solution turns dark blue.

[Co(H2O)6]2+ 4Cl- CoCl4 2- + 6H2O

50
Q

Cobalt (II) ions and ammonia

A

Small amount: Green precip of hydroxide
Excess: Straw coloured solution is formed
[Co(H2O)6]2+ + 6NH3 [Co(NH3)6]2+ + H2O

51
Q

Test for iron (III) ions using SCN-

A

[Fe(H2O)6]3+ + SCN- [Fe(SCN)(H2O)5]2+ + H2O

Yellow/orange solution turns deep blood red

52
Q

What is the equation for Kstab?

A

[new complex]/[aqua complex][new ligands]^no. of moles of ligand in eqn.

53
Q

What does large Kstab value show about equilibrium?

A

The position of equilibrium lies to the right

54
Q

What does a large Kstab value show about stability and formation of ion?

A

Complex ions with larger Kstab values are more stable than those with lower ones, large stability shows that the ion is easily formed

55
Q

What is structure of cis-platin?

A

Square planar, Pt at centre, 2 NH3, 2 Cl

56
Q

What is use of cis-platin?

A

Treatment of cancer

57
Q

How does cis-platin work?

A

Binds onto the DNA of cancerous cells, preventing division and ultimately triggering cell death

58
Q

Problems with cis-platin?

A

Unpleasant side effects

59
Q

Cis-platin ligand sub.

A

A Cl is subbed for water which can subsequently be lost and cis-platin binds to DNA

60
Q

What is carboplatin and what is its advantage?

A

Fewer side effects and lower doses. Cl s in cis-platin replaced by bidentate structure.

61
Q

What is haemoglobin?

A

A complex protein composed of four polypeptide chains.

62
Q

Characteristic of haem groups?

A

Fe2+ ion in at centre

63
Q

How does haemoglobin work?

A

Oxygen binds to Fe2+ ion, as blood passes through the lungs, the haemoglobin picks up oxygen and carries it to the cells to be released. CO2 can be picked up and taken to lungs

64
Q

Structure of coordinate bonds formed around Fe2+ in haem group

A

4 N: groups in corners of parallelogram, globin and O2

65
Q

What is it that allows CO, H2O and O2 to bind to Fe2+ ?

A

Lone pairs of electrons

66
Q

Haemoglobin sub.

A

H2O replaced by O2

67
Q

CO problem

A

Binds more strongly than oxygen (much higher Kstab). Substitution is irreversible. Starves respiring tissues of oxygen

68
Q

What to talk about with altitude

A

Equilibrium with haemoglobin oxygen ligand sub.

A2 CHEMISTRY (16 decks)

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