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H2 Inorganic Chemistry > Transition Metals > Flashcards

Transition Metals Flashcards

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1
Q

Transition element

A

d-block element which forms one or more stable ions with partially filled d subshell

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2
Q

Ligand

A

molecule or anion that has at least one lone pair of electrons for dative bond formation with a transition metal atom or ion

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3
Q

Complex

A

A species which consists of a central metal atom or ion surrounded by ligands which are bonded to it by dative bonds

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4
Q

Electronic configuration trend across the period

A
  • Across the period, additional electrons enter the penultimate 3d
    subshell
  • When forming ions, 4s electrons are removed first before removing
    3d electrons
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5
Q

Atomic radius/First I.E. across the group

A
  • Across the period, atomic radius is relatively invariant
  • Additional electrons enter the** penultimate 3d subshell**, increasing
    the shielding effect     between the nucleus and out 4s electrons
  • Thus the increase in nuclear charge is nullified by the increase in
    shielding effect
  • Hence there is insignificant increase in ENC across the period
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6
Q

Second I.E.

A
  • Greater than first I.E. M+ion > M
  • Second I.E. of Cr and Cu are higher than expected as 3d electron is
    removed instead of 4s
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7
Q

Third and higher I.E.

A
  • Valence 3d electrons removed
  • Across the period NC increases
  • Shielding effect constant
  • I.E. increase across the period
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8
Q

Melting point

A
  • Higher than s-block elements
  • Both 4s and 3d electrons can delocalise as they are close in energies
    to form stronger metallic bonds (s-block only 2 valence electrons
    delocalise)
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9
Q

Density

A
  • Higher than s-block element
  • Increases gradually across the period
  • Greater relative atomic mass to atomic radius ratio
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10
Q

Variable oxidation state

A
  • Both 3s and 3d electrons can be used for bond formation as they
    are close in energies
  • Vacant 3, 4s or 4p orbitals available for bond formation
  • Maximum oxidation state = 4s electrons + unpaired 3d electrons
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11
Q

Coloured complexes

A
  • Degenerate 3d orbitals in octahedral complexes are split into 2
    different energy levels     due to presence of ligands (d-d splitting)
  • A 3d electron from the lower energy level is promoted to the upper
    energy level by absorbing energy from the visible regions of the
    electromagnetic spectrum    , known as d-d transition
  • Only possible with partially-filled d subshell configuration
  • The complement of the colour absorbed is seen
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12
Q

Homogeneous catalysts

A
  • A homogeneous catalyst is in the same phase as the reactants
  • Transition metals or their ions can act as homogeneous catalysts as
    they are able to assist in transferring electrons in redox reactions
    due to their variable oxidation states
  • They work by reducing or oxidising the reactants
  • Lowering the Ea of the reaction
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13
Q

Heterogeneous catalysts

A
  • A heterogeneous catalyst is in a different phase as the reactants
  • Transition metals can act as a heterogenous catalyst as they can
    form weak bonds with reacts molecules using their partially filled 3d
    subshell.
  • Hence reactant molecules can be adsorbed onto the catalyst
    surface, weakening the covalent bonds within the reactant molecules
  • Adsorption also increases the concentration of the reactant
    molecules at the catalyst surface     and allows the reactant molecules
    to come into close contact with each other and with proper
    orientation     for reaction
  • Lowering the Ea of the reaction
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14
Q

Monodentate ligands

A

Ligands that have one lone pair of electrons to form one dative bond

eg: NH3, H2O, CN-, Cl-

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15
Q

Bidentate ligands

A

Ligands that have two lone pair of electrons to form two dative bonds

eg: ethylenediamine/ethan-1,2-diamine CH2CH2CH2CH2

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16
Q

Hexadentate ligands

A

Ligands that have six lone pair of electrons to form six dative bonds

eg: EDTA (ethylenediaminetetraacetate)

17
Q

Coordination number

A

The number of dative bonds formed by the transition metal atom or ion with the ligands in the complex

Coordination number | Shape
2 | Linear
4 | Tetrahedral
6 | Octahedral

18
Q

Structural requirements for formation of complexes

A
  1. Lone pairs of electrons from ligands
  2. Available vacant orbital from transition metal atoms or ions to
    accommodate the lone pairs from ligands
19
Q

Ligand-exchange reactions

A

Ligands in a complex can be replaced to form a more stable complex or through a shift in equilibrium position

20
Q

LEx in oxyhaemoglobin

A
  • At regions of high concentrations of Osub>2</sub>, it will replace
    water in haemoglobin to form oxyhaemoglobin

haemoglobin + 4O2 ⇄ oxyhaemoglobin + 4Hsub>2</sub>O

  • CN- and CO are toxic since they can be strongly and
    irreversibly bonded     to Fe in haemoglobin
  • When replaced by CN- ligands, the complex becomes
    negative charged. It is harder to add electrons to a negatively than
    the charged ion than to a positively charged ion. Hence it is harder
    to reduce the negatively charged [Fe(CN)6]3-
    than the positively charged [Fe(H2O)
    6]3+
21
Q

Chromium complexes

A

[Cr(H2O)6]3+
green
+3

[Cr(OH)6]3-
dark green
+3

Cr(OH)3
grey green ppt
+3

Cr2O72-
orange
+6

CrO42-
yellow
+6

22
Q

Manganese compounds and complexes

A

Mn2+
colourless
+2

MnO2
dark brown ppt
+4

MnO42-
dark green
+6

MnO4-
purple
+7

23
Q

Iron compounds and complexes

A

[Fe(H2O)6]2+
pale green
+2

Fe(OH)2-
green ppt
+2

[Fe(H2O)6]3+
pale yellow
+3

[Fe(SCN)(H2O)5]2+
blood red
+3

Fe(OH)3
reddish brown ppt
+3

24
Q

Copper compounds and complexes

A

[Cu(H2O)6]2+
pale blue
+2

[Cu(NH3)4(H2O)2]2+
dark blue
+2

[CuCl4]2-
yellow
+2

Cu(OH)2
pale blue ppt
+2

25
Q

Aluminium compounds and complexes

A

[Al(H2O)6]3+
colourless
+3

Al(OH)3
white ppt
+3

[Al(OH)4]-
colourless
+3

26
Q

Silver compounds and complexes

A

[Ag(NH3)2]+
colourless
+1

27
Q

Zinc compounds and complexes

A

[Zn(H2O)6]2+
colourless
+2

Zn(OH)2
white ppt
+2

[Zn(OH)4]2-
colourless
+2

[Zn(NH3)4]2+
colourless
+2

28
Q

d-d splitting

A
  • In a complex, the presence of ligands split the d orbitals of the transition metal atom
    or ion into two energy levels
  • a d electron absorbs certain wavelengths of light energy from the visible region of
    the electromagnetic spectrum
  • The d electron undergoes d-d transition and promoted to a higher energy d orbital
  • The remaining unabsorbed wavelengths are transmitted and the complementary
    colour     of the wavelength of light absorbed is observed
29
Q

Criteria for coloured complexes

A
  1. ligands for d-d splitting to occur
  2. ΔE(difference between two split d orbitals) must be in visible light
  3. Need to have partially filled d-orbitals

H2 Inorganic Chemistry (10 decks)

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