transition elements Flashcards

1
Q

what is a transition element?

A

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

(by this definition, Sc and Zn are not transition elements since they do not form ions with a partially filled subshell)

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2
Q

why are the atomic radii and 1st IE of the transition elements relatively invariant?

A
  • no. of proton increases, NC increases
  • e- are added to inner 3d subshell, inner 3d e- effectively shield outer 4s electrons from the nucleus, cancelling the effect of the increasing NC across the period
  • increase in ENC is insignificant, atomic radii and 1st IE remains almost constant
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3
Q

how does the melting point of transition elements compare to s-block elements (e.g. calcium)

A

first row transition elements have a higher mp than s-block elements
both have giant metallic structures, but transition elements have stronger metallic bonds due to:
- availability of 3d e- for delocalisation in the sea of electrons
- smaller cationic radius
hence more energy is required to overcome the stronger electrostatic forces of attraction

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4
Q

how does the densities of transition elements compare to s-block elements (e.g. calcium)?

A

transition elements are denser than s-block elements, due to smaller cationic size, higher mass, and stronger metallic bonds resulting in closer packing

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5
Q

why are transition elements able to exhibit various oxidation states?

A

due to the close proximity of energy of the 4s and 3d electrons

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6
Q

what is a complex?
CDL

A

a complex is a central metal atom or ion dative bonded to one or more surrounding molecules or anions called ligands

if it has an overall charge, it is a complex ion

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7
Q

what is a ligand?
ILDD

A
  • an ion or molecule,
  • which contains at least 1 atom with a lone pair of electrons,
  • which can be donated into a low-lying vacant orbital of a central metal atom or ion
  • to form a dative covalent bond, resulting in the formation of a complex
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8
Q

what are the different types of ligands?

A
  • monodentate ligand (forms 1 dative bond to a central atom)
  • polydentate ligand e.g. bidentate ligand, tetradentate ligand
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9
Q

what is ligand exchange?

A

when one ligand displaces another ligand from the metal complex

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10
Q

describe what happens when dilute NH3 (aq) is added to a solution containing Cu2+ (aq) until in excess

A

when dilute NH3 (aq) is gradually added, a blue ppt of Cu(OH)2 is first formed
NH3 + H2O ⇌ NH4+ + OH-
[Cu(H2O)6]2+ (aq) + 2OH- (aq) ⇌ Cu(OH)2 (s) + 6H2O (l) ——- eqm 1

when excess NH3 (aq) is added, ligand exchange occurs to form a deep blue solution
[Cu(H2O)6]2+ + 4NH3 ⇌ [Cu(NH3)4(H2O)2]2+ + 4H2O ——- eqm 2

The formation of [Cu(NH3)4(H2O)2]2+ decreases the conc of [Cu(H2O)6]2+, causing the POE of eqm 1 to shift to the left to replenish. thus blue ppt Cu(OH)2 dissolves, forming deep blue solution

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11
Q

why does the intake of carbon monoxide deplete oxygen levels?

A

CO is a stronger ligand than O2, so CO displaces O2 in haemoglobin
CO also bonds less reversibly to haemoglobin

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12
Q

what are the colours of copper compounds?

A

[Cu(H2O)6]2+ : blue
[CuCl4]2-: yellow
[Cu(NH3)4(H2O)2]2+: deep blue
Cu(OH)2: pale blue
CuCl, CuI: white ppt
Cu2O: brick red ppt

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12
Q

describe the splitting of d orbitals into two energy levels
IOEEGS
1) difference between energy level of gas phase and octahedral complex + reason
2) which d orbitals have higher energy level + reason
3) results in?

A
  • in the isolated gas phase, all five partially filled d orbitals are degenerate (have the same energy)
  • in octahedral complexes, the energy of the d orbital is higher that that in the gas phase ion
  • this is due to electronic repulsion between the lp of e- of the ligands and the e- in the d orbitals
  • the energy of the 3dx2-y2 and 3dz2 orbital is greater than the 3dxy,3dxz and 3dyz orbitals
  • this is due to greater electronic repulsion due to the ligands approaching the central ion along the axes
  • this results in the d orbitals splitting into 2 energy levels with a small energy gap between them
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12
Q

explain why a solution is coloured.

A
  • in the presence of aqua ligands, the partially filled d orbitals split into 2 energy levels
  • when an electron from the lower energy d orbitals is promoted to a higher energy d orbital, visible light is absorbed
  • the colour not absorbed is observed
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13
Q

why are some ions containing transition elements colourless?

A
  • no 3d electrons, hence no d-d transition to exhibit coloured complex
  • 3d subshell is fully filled, no vacancy in the higher d-orbitals, no d-d transition
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13
Q

what are the factors that affect the colour of complexes?

A
  • electronic configuration: diff oxidation states have diff colours
  • nature of ligand: different ligands cause different energy gaps, different energy
14
Q

why are transition elements able to act as catalysts?

A
  • ability to exhibit variable oxidation states
  • due to the close proximity of the energies of 4s and 3d electrons which allows them to be lost or shared
15
Q

how does Fe3+ catalyse the reaction between (S2O8)2- and I-

A

the reaction involves 2 negatively charged ions which repel each other, causing rate of reaction to be slow. Fe3+ oxidises I- in step 1, then Fe2+ reduces S2O82- in step 2, regenerating Fe3+. As both steps involve the rxn of oppositely charged ions which attract one another, hence speeding up rate of rxn