5.7 TRANSITION ELEMENTS

D-block elements: - located between group 2 and group 13 - 3rd subshell has the highest energy - electrons added to 3d orbitals - all metallic (high mp and bp, shiny, conduct electricity and heat) - used in coinage, construction, production of tools, electrical cables, water pipes, aerospace industry, medical applications (joint replacement and cosmetic dentistry)

Chromium and copper do not follow the expected principle for electron configuration. This is due to stability, a half filled d5 subshell and a fully filled d10 subshell give additional stability to atoms of Cr and Cu

Configuration of ions: - lose 4s electrons before any others - this means that when forming an atom, the 4s orbital fills before the 3d orbitals but when forming an ion the 4s empties before the 3d

Transition elements are d block elements that form at least one ion with a partially filled d orbital - although scandium and zinc are d block elements they do not match the definition and are not transition elements - scandium only forms Sc3+ by losing two 4s electrons and one 3d electron (removing the 3d orbital) - zinc only forms Zn2+ by the loss of two 4s electrons (leaving a full 3d orbital)

Properties: - form compounds in which the transition element has different oxidation states - they form coloured compounds - the elements and their compounds can act as catalysts

Variable oxidation states: - transition elements form compounds with more than one oxidation state - e.g iron forms two chlorides FeCl2 and FeCl3 - the number of oxidation states increase across the transition elements to manganese, then decreases - all transition elements form compounds with an oxidation number of +2, resulting from the loss of two electrons - each oxidation state often has a characteristic colour - a species containing a transition element in its highest oxidation state is often a strong oxidising agent

Formation of coloured compounds: - compounds and ions of transition elements are frequently coloured - potassium dichromate (VI) is bright orange, cobalt (II) chloride is pink-purple, nickel (II) sulfate is green, whilst hydrated copper (II) sulfate is blue - the solid compounds can be dissolved in water to produced coloured solutions - the colour of a solution is linked to the partially filled d-orbitals of the transition metal ion - the colour of a solution can vary with different oxidation states = e.g iron (II) is pale green, iron (III) is yellow = e.g chromium (III) is green and chromium (VI) is yellow or orange

Transition metals as catalysts: - important catalysts used in a variety of industrial processes and in the lab = the haber process is catalysed by a finely divided iron catalyst = contact process is catalysed by vanadium (V) oxide V2O5 = hydrogenation of vegetable fats in the manufacture of margarine uses a nickel catalyst = catalytic decomposition of hydrogen peroxide forming oxygen uses manganese (IV) oxide MnO2 - heterogenous catalysts ^ - homogenous catalysts = reaction between iodide ions and peroxodisulfate ions S2O8- = the reaction of zinc with acids is catalysed by the presence of Cu2+

Complex ions: - metal ions form complex ions by accepting electron pairs from other ions or molecules - the bonds formed are dative covalent bonds (coordinate bonds) - an ion or molecule (with a lone pair of electrons) that can form such bonds with a transition metal are known as ligands - all complex ions have a metal ion centre of ligands surrounding it (usually 4-6) - the coordination number refers to the number of dative covalent bonds

Monodentate ligands form one dative covalent bond with metal ion Cl- OH - CN- NH3 H20

Bidentate ligands form two dative covalent bonds with metal ion H2NCH2CH2NH2 C2O4^2-

Stereoisomerism: - square planar complexes or the form [MA2B2]^n exist in two forms - at least one pair of identical ligands at 180 = trans - at least one pair of identical ligands at 90 = cis

Optical isomerism: - octahedral complexes with bidentate ligands can exist as a pair of enatiomers (optical isomers)

Properties of ligands: - some ions/molecules like H2O do not make particularly good ligands and can be replaced by better ligands - NH3 is a better ligand due to nitrogen being less electronegative than oxygen - Cl- is a better ligand as it is negatively charged, making it electrostatically attracted to the positive transition metal ion

Cis-platin: - used in medicine as an anti-cancer drug - works by forming a platinum complex inside of a cell which binds to DNA and prevents the DNA of the cell from replication (targets tumour cells) - use can lead to kidney damage

Ti3+ is purple/lilac.

V2+ is purple/lilac.

V3+ is green.

V4+ is blue.

V5+ is yellow.

Cr2+ is blue.

Cr3+ is green.

Cr6+ is orange.

Mn2+ is pink.