transition elements conduct a discussion about the importance of transition elements in health,...

Transition ElementsTransition Elements• Conduct a discussion about the

importance of transition elements in health, industry and the environment.

• Make a list of suggestions.

TRANSITION TRANSITION ELEMENTSELEMENTS

Definition: Definition:

A transition element is a d-A transition element is a d-block element which forms block element which forms

at least one ion with a at least one ion with a partly filled d-orbital.partly filled d-orbital.

General propertiesGeneral properties• i. Good catalysts• ii. form coloured compounds• iii.form complex ions• iv. have more than one oxidation

state.

Electronic Configuration.Electronic Configuration.• Vanadium• 1s22s2 2p63s23p64s23d3

• Etc – BUT chromium and copper have full/half full d shells and a 4s1 configuration

• Chromium 1s22s2 2p63s23p6 4s13d5

• Copper 1s22s2 2p63s23p6 4s13d10

Ionisation:Ionisation:• ALWAYS lose the 4s electrons first

and then the 3d electrons.

scandium and zincscandium and zinc• are not transition elements• Sc3+ is d0, Zn2+ is d10

Definition of Oxidation State (number) :Definition of Oxidation State (number) : The The number of electrons that atoms have to lose or gain number of electrons that atoms have to lose or gain or share when they form ionic or covalent bonds in or share when they form ionic or covalent bonds in

compounds.compounds. • variable oxidation states:• All form +2 OS except Sc (loss of 4s

electrons)• Max OS in theory is loss/use of 4s and 3d

electrons. • This is achievable up to Mn (+7)• OS’s between +2 and max• Successive ionisation energies are quite

similar

Determining oxidation Determining oxidation statesstates

• Rules for working out Oxidation Numbers.• Uncombined elements: have oxidation numbers of zero (0).• Simple Ions e.g. Na+: the charge on the ion(1+) is the oxidation

number of the element(+1)• so group 1, 2 and 3 elements have oxidation numbers of 1, 2

and 3 respectively when • combined in compounds.• Fluorine: when combined ALWAYS has an oxidation number of –

1 (it is the most electronegative element).• Oxygen: when combined, has an oxidation number of –2 EXCEPT

in peroxides (O22-) when it is –1 and when combined with fluorine when it will be positive e.g. OF2 oxidation number is +2.

• Hydrogen: when combined, usually has an oxidation number of +1 unless it is combined with a more electropositive metal, e.g. in metal hydrides such as sodium hydride NaH when it is –1.

• Chlorine: when combined, is always –1 EXCEPT when combined with OXYGEN, FLUORINE or NITROGEN.

ExamplesExamples• K2Cr2O7

• Na2S2O3

• FeCl4-

• [Fe(CN)6]4-

Use of oxidation numbers in Use of oxidation numbers in equationsequations

• See “Oxidation states and applications”

Reaction between hydrogen peroxide Reaction between hydrogen peroxide and sodium potassium tartrateand sodium potassium tartrate

• This produces CO2 gas

• Catalysed by Co2+

• Watch for colour change!

Complex ionsComplex ions• Definition of a “Complex”:• A complex consists of a central metal

ion which has species (ions or molecules known as ligands) datively bonded to it.

• Ligand – species forming dative bond to central metal ion in a complex

A huge variety of complexes A huge variety of complexes existsexists

Precipitation – meet Sid.Precipitation – meet Sid.• TM ions in solution exist as hexaaqua

ions, i.e. complex ions

• [M(H2O)6]n+ - Sid.

• This is the species which reacts with NaOH, NH3, conc HCl etc etc

Draw a labelled diagram of Draw a labelled diagram of Sid-e.g. hexaaquacopper(II)Sid-e.g. hexaaquacopper(II)

• Show and label (key) all bonds• Show, in mechanism style, the effect

of sodium hydroxide when its addition produces a precipitate

• Write the equation for the reaction above

• Write the corresponding equation for Fe3+(aq), Cr3+(aq) dropwise then excess

Deprotonation reactionsDeprotonation reactions• [Fe(H2O)6]2+aq+2OH-(aq) Fe(OH)2(H2O)4(s)+ 2H2O

• green ppt.

• [Fe(H2O)6]3+aq+3OH-(aq)Fe(OH)3(H2O)3(s) + 3H2O

• red/brown ppt.• These reactions can be brought about by any alkali• Note: the above green ppt readily oxidises to the brown ppt

suggesting that Fe3+ is more stable than Fe2+ - why?

• See questions on page 5 of notes

LigandsLigands• Ligand definition:- A species with a

lone pair of electrons which it can donate to a central metal ion to form a co-ordinate or dative bond in a complex.

• Examples of ligands• water : aqua,• ammonia(NH3) is ammine,• chloride ion(Cl-) is chloro.

Ligand exchange reactionsLigand exchange reactions• These sometimes follow precipitation

reactions• Consider the reaction between

copper(II) sulphate and NH3(aq) – an alkali:

• Write the equation for the initial reaction (ppt) and draw out the product

Ligand exchange reactionsLigand exchange reactions• On adding excess NH3 ligand

exchange occurs – 2 H2O’s and 2 OH- ions are replaced by NH3

• Draw out the complex formed• For nickel all ligands are replaced by

NH3. • Write equations for the formation of

the ppt (dropwise NH3) and its subsequent reaction on xs NH3

Ligand exchange reactionsLigand exchange reactions• Ligand exchange = replacement of

one type of ligand by another• Further example: (no ppt)• [Cu(H2O)6]2++4Cl- [CuCl4]2-+ 6H2O

• blue yellow• Reagent c.HCl (high [Cl-])• Cobalt (II) ions undergo a

corresponding reaction. Write the equation. Look up colour change

• See questions on page 10 of notes

Naming complex ionsNaming complex ions

• [Cu(H2O)6]2+

• hexaaquacopperII ion. • tetrachlorocuprate(II) – the final

number is the oxidation state of the central metal ion, NOT the charge on the complex.

• [CuCl4]2-

• See q’s on page 6 of notes

Polydentate ligandsPolydentate ligands• Ethanediamine/ethylenediamine –

bidentate ligands (abbreviated – “en”)

4-coordinate, square planar, mixed 4-coordinate, square planar, mixed mono and bidentate ligandsmono and bidentate ligands

Cis and trans in complexesCis and trans in complexes• How might this occur in complexes

where there are two different ligands? [at least two shapes need to be considered, use NH3 and Cl- as ligands]

Cis-trans isomers – Cis-trans isomers – octahedral complexoctahedral complex

Cis-trans isomers – square Cis-trans isomers – square planar complexplanar complex

• Cis platin – anti cancer drug

Draw trans-platinDraw trans-platin

Polydentate ligands exist, e.g. Polydentate ligands exist, e.g. a hexadentate ligand EDTAa hexadentate ligand EDTA

Create a diagram showing a NiCreate a diagram showing a Ni2+2+ ion ion with 3 ethanediamine ligandswith 3 ethanediamine ligands

• [Ni(en)2Cl2]2+

[Ni(en)[Ni(en)33]]2+2+

Draw the mirror image of the Draw the mirror image of the Ni complexNi complex

• Are they superimposable?• No, so they are? • Optical isomers

• Now try Co(en)2Cl2

two types of isomerism in two types of isomerism in one complex systemone complex system

• See questions on pages 8&9 of notes.

Cis-platin, note geometric Cis-platin, note geometric isomerismisomerism

• Anti-cancer drug – binds to DNA causing inaccurate copying of DNA so cells cannot be replicated.

CatalysisCatalysis• Definition of a catalyst:• A species which provides a reaction

with a route of lower activation energy

• Opposite of a catalyst?• Inhibitor

Catalysts Catalysts • They provide sites at which reactions take

place by making temporary bonds with reactant molecules.

• Can be heterogeneous – meaning?• Catalyst in different physical state to

reactants• Adsorptionbonds in reactants

weakenedreactiondesorption• Can be homogeneous (same physical

state) e.g. Cu2+(aq) catalysing HCl(aq) and Zn

Why are TM’s often effective Why are TM’s often effective as catalysts?as catalysts?

The elements or compounds can often be effective catalysts for two reasons.1, They can have several oxidation states so electrons can easily be transferred. This provides a route of lower activation energy which speeds up the reaction.

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