24) Transition elements Flashcards by Jasmine Mussell

For which two elements does the expected principle of electrons filling singly in orbitals before pairing does not apply?

Chromium (3d5 4s1) and Copper (3d10 4s1)

the 1/2 full or fully filled 3d sub-shell to give additional stability

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Define transition element

a d-block element which forms an ion with an incomplete d-sub-shell
(not Sc -> Sc3+ or Zn -> Zn2+)

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Give 3 features of transition elements

form compounds in which the transition element has different oxidation states
form coloured compounds
the element and their compounds can act as catalysts e.g. vanadium (V) oxide in the Contact process - production of sulfur dioxide

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What is a species containing a transition element in its highest oxidation state often?

a strong oxidising agent

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Define complex ion

a transitional metal ion bonded to ligands by coordinate (dative covalent) bonds

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When is a complex ion formed?

when 1 or more molecules / anions (ligands) bond to a central metal ion

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Define ligand

a molecule or ion that can donate a pair of e- to the transitional metal ion

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Define coordinate bond

a shared pair of e- in which the bonded pair has been provided by one of the bonding atoms only

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Define coordination number

the total number of coordinate bonds formed between a central metal ion and ligands

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What is the overall charge of a complex ion?

the sum of the charges on the central metal ion and any ligands present

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Describe the written formula of a complex ion e.g. [Cr(H2O)6]3+

square brackets used to group all of the parts of the complex ion together
ligand inside round brackets
overall charge of complex outside square brackets

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Define monodentate ligand

a ligand that is able to donate 1 pair of e- to a central metal ion

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Give 5 examples of monodentate ligands

H2O:
\:NH3
\:Cl-
cyanide, :CN-
\:OH-

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Define bidentate ligand

a ligand that can donate two lone pairs f e- to the central metal ion, forming two coordinate bonds

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Give 2 examples of bidentate ligand

1,2-diaminoethane
ethanedioate ion (oxalate ion)

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What does the shape of a complex ion depend upon?

its coordination number

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Six-coordinate complexes can form which shape?

octahedral

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Four-coordinate complexes can form which 2 shapes?

tetrahedral

square planar

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In which complex ions does a square planar shape occur?

in those of transition metals with 8

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Describe cis-trans isomerism in octahedral complexes with monodentate ligands

4 of 1 type of ligand and two of another type of ligand

Describe optical isomerism in octahedral complexes

contain 2 or more bidentate ligands

‘cis’ isomers only

What are trans-isomers of octahedral complexes unable to show optical isomerism?

mirror image is exactly the same and can be superimposed

Describe the role of cis-platin in cancer treatment?

forms a platinum complex inside of a cell which binds to DNA, preventing DNA replication
activation of the cell’s own repair mechanism leads to apoptosis

Define ligand substitution

a reaction in which one or more ligands in a complex ion are replaced by different ligands

What colour is [Cu(H2O)6]2+ as a solution?

pale blue

What happens to [Cu(H2O)6]2+ upon small addition of NH3?

Cu(OH)2, copper (II) hydroxide forms | pale blue ppt

What colour is [Cu(H2O)6]2+ as a solution?

pale blue

What happens to [Cu(H2O)6]2+ upon small addition of NH3?

Cu(OH)2, copper (II) hydroxide forms | pale blue ppt

What happens to [Cu(H2O)6]2+ in excess of NH3?

[Cu(NH3)4(H2O)2]2+ dark blue solution 4 ammonia ligands replace 4 of the water ligands

What happens to [Cu(H2O)6]2+ upon small addition of NH3?

Cu(OH)2, copper (II) hydroxide forms | pale blue ppt

What colour is [Cr(H2O)6]3+ as a solution?

violet

What happens to [Cr(H2O)6]3+ upon small addition of NH3?

Cr(OH)3, chromium (III) hydroxide | grey-green ppt

What happens to [Cr(H2O)6]3+ in excess of NH3?

[Cr(NH3)6]3+ | dark purple solution

What happens to [Cr(H2O)6]3+ in excess of NH3?

[Cr(NH3)6]3+ | dark purple solution

What colour is chromium (III) sulfate dissolved in water? | [Cr(H2O)5 SO4]+

green solution

What happens to [Cu(H2O)6]2+ in conc. HCl?

[CuCl4]2- yellow solution (if not carried out to completion intermediate = green) tetrahedral shape 6 water ligands have been replaced by 4 chlorine ligands chlorine ligands are larger in size so fewer can fit around the central Cu 2+ ion

Describe ligand substitution with relation to haemoglobin

CO can bind by ligand substitution to form carboxyhaemoglobin (irreversible) if CO conc is too high, transport of O2 is prevented - leading to death

Define precipitation reaction

the formation of a solid from a solution during a chemical reaction

When are precipitates often formed?

when two aqueous solutions are mixed together

What happens to Cu 2+ on the small addition of OH- ?

Cu(OH)2 | pale blue ppt

What happens to Cu 2+ on the small addition of OH- ?

Cu(OH)2 | pale blue solution -> pale blue ppt

What happens to Cr 3+ on the small addition of OH- ?

Cr(OH)3 | violet solution -> grey-green ppt

What happens to Fe 2+ on the small addition of OH- ?

Fe(OH)2 iron (II) hydroxide pale green solution -> green ppt

What happens to Fe 3+ on the small addition of OH- ?

Fe(OH)3 iron (III) hydroxide yellow/orange solution -> orange-brown ppt

What happens to Mn 2+ on the small addition of OH- ?

Mn(OH)2 manganese (II) hydroxide pale pink solution -> light brown ppt

What happens to Cr 3+ upon an excess of OH- ?

[Cr(OH)6]3- | dark green solution

What is significant about the reactions of Fe2+, Fe3+ and Mn2+ with aqueous ammonia?

they react in the same way as with aqueous sodium hydroxide, forming precipitates

Standard electrode potentials can be used to explain _. The more positive the E⦵ value, the more likely equilibrium is to _ electrons, shift to the _ and undergo _.

redox reactions gain RHS reduction

Suggest why vanadium does not form ions in which vanadium has an oxidation state greater than +5?

only 5 e- in 4s and 3d sub-shells