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Bellas chemistry > Topic 15.1 Transition Metals > Flashcards

Topic 15.1 Transition Metals Flashcards

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1
Q

Transition metals outline

A
  • Variable oxidation states
  • Partially filled d orbitals
  • Lost electrons; s orbitals removed first
  • Similar properties: atomic radius, high density, high melting point/boiling point
  • Form complexes
  • Make coloured ions in solution
  • Good catalyst
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2
Q

Complexes

A
  • Central ion surrounded by ligands
  • Ligands: H2O, Cl-, NH3, OH- (monodentate)
  • Dative covalent bond
  • Bidentate (eg. NH3CH2CH2NH2 lone pairs on each side)
  • Octahedral: H2O, NH3, OH-
  • Tetrahedral: Cl-
  • Co-ordination number is the amount of ligands
    silver: 2
    platinum: 4
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3
Q

Coloured ions

A
  • In transition metals
  • Ligands cause d orbitals to split
  • Some electrons will be in a higher energy levels
  • Ions can be colourless if no electrons to exite (eg. zinc- completely filled d orbitals)
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4
Q

Square planar

A
  • 90°
  • cis-platin (hair loss symptom- administer in small doses)
  • platinum
  • nickel
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5
Q

Ligand substitution

A
  • Exchange ligands
  • eg. Haem –> multidentate, Fe
    Oxygen substituted by carbon monoxide
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6
Q

Amphoteric metal hydroxide

A

Cr(OH)3(H2O)3 + 3H+ —> [Cr(H2O)6]3+ (?)
Cr(OH)3(H2O)3 + 3OH- —> [Cr(OH)6]3- + 3H2O (acts as acid-donates protons(?))

  • ability of a species to react with both acid and bases.
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7
Q

Chelete effect

A
  • Positive entropy- more favourable (higher the entropy, the more favourable it is).
  • Greater entropy change, greater Gibbs free, more favourable.
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8
Q

Characteristics of transition metals

A
  • Hard solids
  • Have high mpt/bpt
  • Can act as catalysts
  • Form coloured ions and compounds
  • Form ions with different oxidation numbers
  • Form ions with incompletely-filled d-orbitals
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9
Q

Symbols and equations with ligands

A
  • The relatively small size of transition metal ions enables them to attract electron-rich species more strongly, including the water molecules present in aqueous solutions.
  • These water molecules are attracted to the transition metals are attracted to the transition metal ions so strongly that they form a specific number of bonds, usually 6.
  • These electron-rich species that can form dative bonds in the same way, are called ligands. The complete formulae are called complexes (complex ions).
  • The total number of dative bonds around the metal ion is called the coordination number.
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10
Q

Examples of ligands

A
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11
Q

Naming complexes

A
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12
Q

Colour depends on electrons in 3d energy levels

A

If one of the electrons in the lower energy level absorbs energy from the visible spectrum, it can move to the higher energy level (‘excited’ state).
- When an electron moves to a higher energy level, the amount of energy it absorbs depends on the difference in energy between two levels- the bigger the energy difference, the more energy the electron absorbs.

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13
Q

Predicting shapes if complexes: using VSEPR theory

A

Count the number of electrons donates by the ligands.

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14
Q

Predicting the shapes of complexes: octahedral complexes

A
  • The most common ligands in most octahedral complexes are water, ammonia and the hydroxide ion.
  • Although these ligands have different numbers of lone pairs of electrons, each ligand uses only one lone pair to forma coordinate bond with a transition metal ion.
  • As they contain six ligands, the complexes are sometimes described as having six-fold coordination.
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15
Q

Predicting the shape of complexes: Tetrahedral and linear complexes

A
  • The only tetrahedral complexes needed are chloride ions.
  • Chloride ions are much bigger than water etc so there is insufficient room around the central metal ion for six chloride ions to act as ligands.
  • The only linear complex needed is the reactive ion present in Tollen’s reagent (ammoniacal silver nitrate).
  • The Ag+ ion has only two ligands.
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16
Q

Predicting the shape of complexes: Square planar molecules

A
  • Example of a square planar shape is xenon tetrafluoride (XeF4).
  • The four bonding pairs are in a plane, with four fluorine atoms at the corners of a square
  • Bond angle: 90°
17
Q

Predicting the shape of complexes: Cis-platin

A
  • Four ligands in this complex form a square planar shape, and not a tetrahedral shape.
  • Effective treatment for some types of cancer.
18
Q

Cis-trans isomers

A
  • Cis-platin and trans-platin isomers
  • Consist of: a platinum(II) ion, two chloride ligands and two ammonia ligands.
  • The cis- prefix indicates that identical ligands are next to each other.
  • The trans- prefix indicates that they are opposite to each other
19
Q

Denticity

A
  • Monodentate ligands: ligand uses one pair of electrons on one atom to form the dative bond with the metal ion.
  • Bidentate ligand: has two atoms, each of which uses a one pair of electrons to form a dative bond with the metal ion.
  • Multidentate ligand: a ligand with several atoms, each of which uses a lone pair of electrons to form a dative bond with metal ion.
20
Q

Bidentate ligands

A

When it acts as a bidentate ligand, it uses the lone pair of electrons on each nitrogen atom to attach to the metal ion.

21
Q

Multidentate ligands

A
22
Q

The stability of complexes

A
  • The ‘stability’ refers to the stability of two complexes in which the number of ligands has changed.
  • Ligand exchange reactions lead to an increase in stability of the products compared to the reactants, and so formation of the products is favoured.
  • When a mono dentate ligand is replaced by a multi dentate ligand, the increase in stability is even greater.
23
Q

Haemoglobin and oxygen transport

A

In a haem group 4 n atoms hold Fe2+ ion by forming dative bonds in the square planar structure.
- Fifth dative bond from protein to Fe2+ ion.
- Oxygen binds by becoming ligand to Fe2+.
- Reversible reaction as bond is weak.

24
Q

Haemoglobin and carbon monoxide

A
  • Lone pair on carbon that forms ligand.
  • Strong bond between carbon and oxygen so takes oxygen from Fe2+.
  • Ligand substitution.
  • Non reversible reaction.
  • Once the carboxyhemoglobin is formed, the dative bond is so strong that it doesn’t break easily.
  • Haemoglobin + carbon monoxide –> carboxyhaemoglobin (whereas: Haemoglobin + oxygen ⇌ oxyhaemoglobin).
25
Q

equation linking energy and frequency of light

A

ΔE = h𝝂
where ΔE = change of energy
h = Planck’s constant (6.62607015×10^−34)
𝝂 = frequency

26
Q

what makes colours of transition metals

A
  • d orbitals split due to ligands.
  • Electrons absorb light in the visible region of the spectrum.
  • To promote electrons to higher energy levels.
  • The unabsorbed light is the colour shown/reflected.
27
Q

types of reaction of ligands

A
  • redox
  • acid base
  • ligand exchange
  • coordination number change
28
Q

types of reaction of ligands
-redox

A

The oxidation number of the transition metal ion changes.
- Fe+ (aq) is pale green but when exposed to air turns yellow.
- +2 to +3

29
Q

types of reaction of ligands
-acid base reaction

A

One or more of the ligands gains or looses a hydrogen ion
- Hexaaquacopper ions react with hydroxide ions OH- remove hydrogen ions from water ligands attached to copper in acid base.
- Insoluble neutral complex formed - blue precipitate.

30
Q

types of reaction of ligands
-ligand exchange

A

One or more of the ligands around the central transition metal is replaced by a different ligand.
- When excess ammonia is added to hexaaquacopper ions ligand exchange occurs deep blue solution of tetraaminediaquacopper formed.

31
Q

types of reaction of ligands
-coordination number change

A

The number of ligands changes.
- Concentrated HCl added to hexaaquacopper the six water are replaced by four chlorine.
- Blue to green to yellow.
- Coordination 6-4.

Bellas chemistry (32 decks)

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