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Transition Metals:
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Found in the d-block
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Transition metals-d-block elements that can form one or more stable ions with incompletely filled d-orbitals
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, act as catalysts
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For each ion the oxidation no of the metal changes
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Chromium has 1 electron in 4s orbital and one in each orbital of 3d subshell
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Scandium only forms one ion
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When it loses the electrons, it ends up with electronic
configuration of argon
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When it loses electrons, they are lost from 4s subshell keeping 3d subshell
full
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They are similar energy level
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The energy released when ions form complex or compound increases with the ionic charge
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Complex ions:
Complex ion- A metal ion surrounded by dative covalently (coordinated) bonded ligands
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It lust have at least one lone pair of

electrons, otherwise it won’t have anything to form a dative covalent bond with
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They can form 2 dative covalent bonds with a metal ion
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E
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EDTA4- has 6 lone pairs (hexadentate)
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Haemoglobin is used to transport oxygen around the body
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It’s made of a ring containing 4 N atoms
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There are 2
other ligands bonded to iron
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The overall charge on the complex ion is its ON
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Complex ions can have different no of ligands
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The usual

Hydroxide

-OH

+1

Hydroxo

coordination no are 6 and 4
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If they are larger

Chloride

Cl-

-1

Chloro

only 4 can fit
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They form distinctive shapes depended on their
coordination no to position ligands as far away from each other as possible
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Four-fold coordination usually means a tetrahedral shape
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5 degrees
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The bond angle is 90 degrees – cis-platin is an example
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Cis-platin is used in cancer treatment rather than trans-platin since it’s less toxic and it can form the bond with 2 strands of DNA which
prevents them from separating and thus prevents cells from dividing
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Complex ions and colours:
Ligands split the 3d orbitals into two different energy levels
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To jump up to the higher orbitals they need energy equal to the energy gap
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The larger the energy gap the higher the frequency of light that is absorbed
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The splitting causes some frequencies to be absorbed and the rest of
frequencies of light are transmitted
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A colour wheel shows complimentary colours
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If that’s the case the
compound will look white or colourless
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The colour can help to
identify the transition metal
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(+2,
+3, +4, +5)

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Reduction potentials can be used to see if the reactions are likely to happen
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+6

Cr2O72-

Orange

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It forms two ions with oxygen in the +6

+6

CrO42-

Yellow

ON
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They are

+2

Cr2+

Blue

good oxidising agents because they are easily reduced to Cr3+
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Dichromate (VI) ions can be reduced using a reducing agent such as zinc and dilute acid
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Inert

Cr2O72- + 14H+ + 3Zn → 3Zn3+ + 2Cr3+ + 7H2O

ON= +6 → + 3

atmosphere will have to be used or it

2Cr3+ + Zn → Zn2+ + 2Cr2+

ON= +3 → + 2

would be oxidised back to Cr3+
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If acid is added to this yellow solution, an orange solution which contains dichromate (VI) ions is formed
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Chromium Hydroxide is amphoteric
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It can react with both bases and acids
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If excess NaOH is added to the precipitate the OH- ligands deprotonate and a solution containing [Cr(OH)6]3- forms
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They are not ligand exchanges
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But if excess ammonia is added to the precipitate a ligand exchange occurs and [Cr(NH3)6]3+ forms
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Preparation of chromium (II) ethanoate:
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Orange sodium dichromate (VI) is reduced with zinc in acid solution to form a green solution containing Cr3+ ions and then to
give a blue solution containing Cr2+ ions
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2Cr2+ + 4CH3COO- + 2H2O → [Cr2(CH3COO)4(H2O)2](s)

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The experiment must be made in inert atmosphere
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Zinc will also react to produce some
hydrogen gas which can escape through the rubber tube into a beaker of water
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The build up of pressure in the flask will force Cr2+ solution through the open glass tube and into a flask of sodium ethanoate
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Filter off the precipitate and wash it using water, then ethanol, then ether (still has to
be in an inert atmosphere)
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It usually causes a change of colour
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If small ligand is substituted for large, charged ligand, there’s a change of
coordination no and shape
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Carbon monoxide poisoning happens because of ligand exchange
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CO forms a strong dative covalent bonds with the
iron ion and doesn’t readily exchange with oxygen or water ligands, meaning the haemoglobin
can’t transport oxygen anymore
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When a ligand exchange reaction occurs, dative bonds are broken and formed
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So the enthalpy
change for a ligand exchange reaction is usually very small
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Reactions that result in
an increase in entropy are more likely to occur and complex formed is more stable
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When you mix an aqueous solution of transition element ions with aqueous NaOH or aqueous ammonia, the water ligands are
deprotonated, and you get a coloured hydroxide precipitate
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Transition metals and their compounds make good catalysts because they can change oxidation no by gaining or losing electrons within
their d-orbitals
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Homogeneous catalysts are in the same physical state as the reactants
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The activation energy needed to form intermediates is lower than that needed to make the products directly from the reactants
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Autocatalysis – When a product catalyses the reaction
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Heterogeneous catalyst- In different phase from reactants
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Reaction occurs on the
surface of catalyst
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Catalytic converters are used in cars to reduce emission of nitrogen monoxide and carbon monoxide produced by internal combustion
engines
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2NO + 2CO → N2 + 2CO2
1
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– adsorption
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The surface of catalyst activates the molecules so they react more easily
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3
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– desorption

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