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Chemistry > Transition Elements A2 > Flashcards

Transition Elements A2 Flashcards

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1
Q

Why is the d block called the d block?

A

Because the highest energy electrons are in the d subshell.

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2
Q

What is a transition element?

A

A d block element that forms an ion with an incomplete d-subshell.

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3
Q

What elements found in the d block are not transition elements?

A

Scandium and Zinc.

Sc’s only ion is Sc3+ (empty sub-shell).
Zn’s only ion is Zn2+ (full sub-shell).

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4
Q

What are the physical properties of transition metals? Explain.

A
  • Good conductors of heat and electrcity.
  • Hard, strong and shiny
  • High b.p and m.p

Hardness and high m.p and b.p is due to strong metallic bonds.
Both 4s and 3d available to take place in delocalisation into a ‘sea of electrons’ - giving strong metallic bondings and ability to conduct electricity.

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5
Q

What are the chemical properties of transition metals?

A
  • Variable in oxidation state
  • Colour
  • Catalysts
  • Complex formation
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6
Q

Why do TMs have variable oxidation states?

A

TMs can use both 3d and 4s electrons in bonding. This means they can form ions of roughly the same stability by losing different numbers of electrons.

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7
Q

For what 2 reasons do TMs make efficient catalysts? Give an example of a process catalysed by a transition metal.

A
  • 3d electrons enable TMs to form temporary bonds so reactants are held in place.
  • As they have several oxidation states they can participate in electron transfer processes, thus providing an alternative route for the reaction.

e.g. Contact process
2SO2 + O2 <–> 2SO3
Catalysed by Vanadium (V) oxide

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8
Q

How can you simplify writing the electron structure for transition elements?

A

Writing [Ar] and carrying on from there.

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9
Q

What are complex ions?

A

When species called Ligands form coordinate (dative) bonds to a central metal ion.

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10
Q

What is a ligand?

A

A molecule or ion that can donate a pair of electrons to a central metal ion to form a coordinate bond.

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11
Q

What is the coordinate number?

A

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

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12
Q

What are ligands with one / two coordinate bonds called?

A

Monodentate
Bidentate

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13
Q

What usually are the shape of complexes with H2O or NH3?

A

Octahedral

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14
Q

What shape are 4-coordinate complexes?
What is the exception?

A

Square planar
Complexes with 4 Cl- are tetrahedral due to it’s larger size.

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15
Q

Complex ions can also show 2 types of stereoisomerism. What are they?

A

Cis-trans isomerism - for both monodentate and bidentate

Optical Isomerism

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16
Q

What is Cis-platin?
- Structure
- Use / function

A
  • Square planar complex ion .
  • Platinum metal ion, 2Cl- and 2 NH3-
  • Cis-trans isomerism

CIS-platin
- one of the most successful anticancer drugs
- acts by bindings to DNA of fast growing cancer cells, preventing DNA replication and cell division.

(ASK BEN IF WE NEED TO KNOW ABOUT THE DISCOVERY)

17
Q

What are the requirements for optical isomerism?

A
  • Octahedral complex
  • A complex with 3 bidentate ligands OR
  • A complex with 2 bidentate ligands and 2 monodentate ligands

Non-superimposable - ASK BEN

18
Q

What is another name for optical isomers?

Are they superimposable?

A

Enantiomers

Non-superimposable mirror images of each other

19
Q

What is a ligand substitution reaction?

A

When a ligand in a complex is replaced by another ligand.

20
Q

What are the colour changes that occur in the ligand substitution when aq Cu(II) reacts with ammonia?

What are the 2 steps and ionic equations?

A

Pale blue sol to pale blue ppt to dark blue sol

+ Small amount of ammonia
Pale blue ppt forms
[Cu(H2O)6]2+ + 2NH3–> [Cu(H2O)4(OH)2)] + 2 NH4+

+ Excess ammonia
ppt dissolves in excesss ammonia to form dark blue solution.
[Cu(H2O)4(OH)2) + 4 NH3 –> [Cu(H2O)2(NH3)4]2+ + H2O + 2OH-

21
Q

Describe the colour change when aq Cu (II) is reacted with HCl.

What is the ionic equation?

A

Pale blue sol -> yellow sol

[Cu(H2O)6]2+ + 4Cl- –> [CuCl4]2- + 6H2O

22
Q

Describe the colour change when Cr (III) is reacted with ammonia.

What are the two steps and ionic equations?

A

+ Small amount of ammonia
Violet sol –> grey-green ppt
[Cr(H2O)6]3+ + 3NH3 –> [Cr(H2O)3(OH)3] + 3NH4+

+ Excess ammonia
Grey-green ppt dissolves in ammonia to form –> Purple sol
[Cr(H2O)3(OH)3] + 6NH3 –> [Cr(NH3)6]3- + 3H2O + 3OH-

23
Q

Describe the structure of haemoglobin.

A

Coordinate bonds between Fe2+ and 4 Nitrogen atoms. A further coordinate bond formed to a protein called globin. A final coordinate bond to an oxygen molecule which is then transported.

Fe2+, 4N, globin and O2 - complex ion

24
Q

What does CO do? What does it form?

A

CO and O2 bind to the same site on haemoglobin. When CO present, ligand substitution occurs and CO binds instead of oxygen.

CO binding to haemoglobin forms carboxyhaemoglobin.

The bond is strong so is not reversible. Starves the tissues of O2, leading to death.

25
Q

What is a precipitation reaction? What do transition metals react with to form ppt?

A

When two aq solutions are mixed and a solid ppt forms.

Transition metals react with NH3 and NaOH to form ppt.

26
Q

What colour changes occur when Fe(II) is reacted with NaOH or NH3?

What are the formulas for the orginal and oxidised ppt?

A

Pale green sol –> green ppt (turns brown on standing as oxidised)

Green ppt = [Fe(H2O)4(OH)2]
Brown oxidised ppt = [Fe(H2O)3(OH)3]
Fe2+ is oxidised to Fe3+

Does not dissolve in excess NaOH or NH3

27
Q

What colour changes occur when Fe(III) is reacted with NaOH or NH3?

A

Pale yellow sol –> orange-brown ppt

Does not dissolve in excess NaOH or NH3

28
Q

What colour changes occur when Cr(III) is reacted with excess NaOH?

A

Violet sol –> grey-green ppt –> dark green sol

29
Q

What colour changes occur when Mn(II) is reacted with NaOH or NH3?

A

Pale pink sol –> light brown ppt (darkens standing on air)

Does not dissolve in excess NaOH or NH3

30
Q

What colour changes occur when Cu(II) is reacted with NaOH or NH3?

A

Pale blue sol –> blue ppt

Does not dissolve in excess NaOH

31
Q

What TMs are soluble in excess NH3? NaOH?
What are the colour changes?

A

Cr(III) and Cu(II) are soluble in excess NH3.
Cr(III) is also soluble in excess NaOH.

Cr(III): violet sol –> grey-green ppt –> dark green sol (+NaOH) OR purple sol (+NH3)

Cu(III): blue sol –> blue ppt –> deep blue sol (+NH3)

32
Q

What always is the formula for ppts formed from transition metal reactions?

A

[M(H2O)6-n(OH)n]

n = charge of M

33
Q

What two transition metals have electron configurations you wouldn’t normally expect? What are they?

A

Cr and Cu.
Half and full subshells are more stable so an electron is stolen from the 4s subshell.

Cr - [Ar] 3d5 4s1
Cu - [Ar] 3d10 4s1

Chemistry (22 decks)

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