Transition Elements Conduct a discussion about the importance of transition elements in health, industry and the environment. Make a list of suggestions.

TRANSITION ELEMENTS Definition: A transition element is a d- block element which forms at least one ion with a partly filled d-orbital.

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

Electronic Configuration. Vanadium 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 3 Etc – BUT chromium and copper have full/half full d shells and a 4s 1 configuration Chromium1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 5 Copper1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 10

Ionisation: ALWAYS lose the 4s electrons first and then the 3d electrons.

scandium and zinc are not transition elements Sc 3+ is d 0, Zn 2+ is d 10

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

Examples K 2 Cr 2 O 7 Na 2 S 2 O 3 FeCl 4 - [Fe(CN) 6 ] 4-

Use of oxidation numbers in equations See “Oxidation states and applications”

Reaction between hydrogen peroxide and sodium potassium tartrate This produces CO 2 gas Catalysed by Co 2+ Watch for colour change!

Complex 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 exists

Precipitation – meet Sid. TM ions in solution exist as hexaaqua ions, i.e. complex ions [M(H 2 O) 6 ] n+ - Sid. This is the species which reacts with NaOH, NH 3, conc HCl etc etc

Draw a labelled diagram of 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 Fe 3+ (aq), Cr 3+ (aq) dropwise then excess

Deprotonation reactions [Fe(H 2 O) 6 ] 2+ aq+2OH - (aq) Fe(OH) 2 (H 2 O) 4 (s)+ 2H 2 O green ppt. [Fe(H 2 O) 6 ] 3+ aq+3OH - (aq)Fe(OH) 3 (H 2 O) 3 (s) + 3H 2 O 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 Fe 3+ is more stable than Fe 2+ - why?

See questions on page 5 of notes

Ligands 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 reactions These sometimes follow precipitation reactions Consider the reaction between copper(II) sulphate and NH 3 (aq) – an alkali: Write the equation for the initial reaction (ppt) and draw out the product

Ligand exchange reactions On adding excess NH 3 ligand exchange occurs – 2 H 2 O’s and 2 OH - ions are replaced by NH 3 Draw out the complex formed For nickel all ligands are replaced by NH 3. Write equations for the formation of the ppt (dropwise NH 3 ) and its subsequent reaction on xs NH 3

Ligand exchange reactions Ligand exchange = replacement of one type of ligand by another Further example: (no ppt) [Cu(H 2 O) 6 ] 2+ +4Cl-  [CuCl 4 ] H 2 O 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 ions [Cu(H 2 O) 6 ] 2+ hexaaquacopperII ion. tetrachlorocuprate(II) – the final number is the oxidation state of the central metal ion, NOT the charge on the complex. [CuCl 4 ] 2-

See q’s on page 6 of notes

Polydentate ligands Ethanediamine/ethylenediamine – bidentate ligands (abbreviated – “en”)

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

Cis 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 NH 3 and Cl - as ligands]

Cis-trans isomers – octahedral complex

Cis-trans isomers – square planar complex Cis platin – anti cancer drug

Draw trans-platin

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

Create a diagram showing a Ni 2+ ion with 3 ethanediamine ligands [Ni(en) 2 Cl 2 ] 2+

[Ni(en) 3 ] 2+

Draw the mirror image of the Ni complex Are they superimposable? No, so they are? Optical isomers Now try Co(en) 2 Cl 2

two types of isomerism in one complex system

See questions on pages 8&9 of notes.

Cis-platin, note geometric isomerism Anti-cancer drug – binds to DNA causing inaccurate copying of DNA so cells cannot be replicated.

Catalysis Definition of a catalyst: A species which provides a reaction with a route of lower activation energy Opposite of a catalyst? Inhibitor

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 Adsorption  bonds in reactants weakened  reaction  desorption Can be homogeneous (same physical state) e.g. Cu 2+ (aq) catalysing HCl(aq) and Zn

Why are TM’s often effective 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.

m/articles/p16.htm Textbook page 22 – 26: SAQ’s

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