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Topic 17 - Transition Elements

Terms in this set (24)

Transition element definition
An element that has partially filled d-orbitals in their atoms or ions
Traits of transition metals
Several different oxidation states
Form complexes through co-ordinate bonding
Can act as catalysts
On ionisation which electron are lost first
4s
How do variable oxidation states lead to catalytic properties
Uses its variable oxidation state to provide an alternative pathway with a lower activation energy
Or the d-orbitals start to bond with the reactants weakening the bonds in the reactants making them react more quickly
Example of catalysis; Haber process for making ammonia from nitrogen and hydrogen
Iron
N₂ + 3H₂ ⇌ 2NH₃
Example of catalysis; The contact process for the manufacture of sulphur trioxide from sulphur dioxide
Vandium (V) oxide (V₂O₅)
2SO₂ + O₂ ⇌ 2SO₃
Complex ion definition
A metal ion surrounded by groups of molecules/atoms bonded together by co-ordinate bonds between the d-orbitals on the ion and lone pairs in the molecular/atoms
Ligand definition
Species which form co-ordinate bond to transition metal ions in a complex
Neutral ligands
Aqua (H₂O) / Ammines (NH₃)
Anionic ligands
Chloro (Cl⁻)
[Cu(H₂O)₆]²⁺
Hexa-aqua-copper (II)
Octahedral 90°
Blue
[Cu(NH₃)₄(H₂O)₂]²⁺
Tetra-ammine-di-aqua-copper (II)
Distroted octahedral
Deep royal blue
[CuCl₄]²⁻
Tetra-chloro-cuprate (II)
Tetrahedral 109.5°
Green
Why can transition elements make complex ions
Partially filled d-orbitals are able to form dative bond to the lone pair on ligands
Bi- and poly-denate ligands definition
Larger ligand molecules that are able to form more than one dative bond
What is the cause of colour in a transition elements
An incomplete d subshell acts as a chromophore
Answer for chromophore
Ligands cause the d orbitals to split into 3 orbitals at the lower and two at the higher energy level.
Electrons at a lower energy level can absorb certain frequencies of light to become promoted to the upper level. Frequencies not absorbed are reflected resulting in the colour of the complex
Reaction of excess sodium hydroxide with Chromium (II), Cr³⁺
Cr(OH)₃ + 3[OH⁻] → [Cr(OH)₆]³⁻
Grey-green ppt → green solution
Colour change of Cr³⁺ with NaOH
Green → Grey-green
Colour change of Fe²⁺ with NaOH
Pale green → Dark green
Colour change of Fe³⁺ with NaOH
Yellow → Dark red
Colour change Cu²⁺ of with NaOH
Blue → Pale blue
Economic importance of transition elements
Chromium - manufacture of stainless steel
Iron - catalyst in the Haber process
Copper - Electrical apparatus
Nickel - catalyst for the hydrogenation of vegetable oils
Biological roles of transition elements
Iron - present in blood
Cobalt - component of B12
Manganate - Found bones, tissues and some organs
Chromium - Cofactor in the insulin hormone system which regulates blood glucose levels
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