What are transition metals PDF

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Transition metal ...

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What are transition metals? The transition elements are found in the d-block of the periodic table

 Across the d-block, the highest energy sub-shell is a d sub-shell  But not all d-block elements are transition elements A TRANSITION ELEMENT IS A D-BLOCK ELEMENT THAT FORMS AT LEAST ONE ION WITH AN INCOMPLETE D SUB-SHELL  Two d-block elements that do not count as transition elements are Scandium (Sc) and Zinc (Zn)  Scandium only forms the Sc3+ ion, with empty d-orbitals  Zinc only forms the Zn2+ ion, with completely full d-orbitals

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Electron configurations [The electron configuration of an element is the arrangement of the electrons in an atom of the element.]  Electrons occupy orbitals in order of energy level  The sub-shell energy levels in the third and fourth energy levels overlap  The 4s sub-shell fills before the 3d sub-shell

 Chromium and Copper are a bit different  Chromium – Has half shell stability  Copper – 3d9 is not very stable What about ions?  Transition metals lose electrons to form positive ions  They lose 4s before 3d electrons  3d and 4s energy levels are very close together

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Properties of T.metal compounds Physical prop erties properties They have normal metal properties      

Shiny Ductile Malleable Good conductors High density High melting point and boiling point

Variable oxid ation states oxidation The transition elements form ions with two or more oxidation states  They all form compounds with ions in the +2 oxidation state o Most of the time, from losing electrons from the 4s orbital o Because they are in the highest occupied energy level  However, 3d and 4s energy levels are close in energy o 3d electrons can also be lost when an atom forms a stable ion

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Coloured compou nds compounds When white light passes through a solution containing transition metal ions, some of the wavelengths of visible light are absorbed. The colour we observe is a mixture of the wavelengths of light that have not been absorbed Partially filled d-orbital = coloured compound

Catalysts Catalysts increase the rate of a chemical reaction by providing an alternative route for the reaction with a lower activation energy. Transition elements and ions are good catalysts  Provide a surface on which a reaction can take place o Reactants adsorb onto the surface of the metal and are held in place while a reaction occurs o Then the products are desorbed and the metal remains unchanged  Can change oxidation states by gaining or losing electrons o They bind to reactants forming intermediates Some examples  Haber process to make ammonia for fertilisers o NH2 + 3H2 ⇌ 2NH3 o Iron catalysts increases rate of reaction and decreases need for heat  Contact process to convert sulphur dioxide into sulphur trioxide in the manufacturing of sulphuric acid o 2SO2 + O2 ⇌ 2SO3 o Catalyst is vanadium(V) oxide V2O5  Decomposition of hydrogen peroxide for making oxygen gas o H202  2H20 + O2 o Reaction sped up with Manganese (IV) oxide, MnO2

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Precipitation reactions [A precipitation reaction is one in which soluble ions, in separate solutions, are mixed together to form an insoluble compound, settling out as a solid. The solid is called a precipitate.] Transition metal ions in aqueous solution react with aqueous NaOH to form coloured precipitates. Ion Cu2+ (aq)

Co2+ (aq)

Fe2+ (aq)

Fe3+ (aq)

Observation with NaOH Blue solution of copper (II) reacts to form a pale blue precipitate. Pink solution of cobalt (II) reacts to form a blue precipitate. Turns beige in air. Pale green solution of iron (II) reacts to form a green precipitate. Turns rusty brown at surface in air. * Pale yellow solution of iron (III) reacts to form a rusty brown precipitate

Equation 2OH-(aq)Cu(OH)2(s) Precipitate is copper (II) hydroxide Cu2+(aq) +

Co2+(aq) + 2OH-(aq)Co(OH)2(s) Precipitate is cobalt (II) hydroxide

Fe2+(aq) + 2OH-(aq)Fe(OH)2(s) Precipitate is iron (II) hydroxide

Fe3+(aq) + 3OH-(aq)Fe(OH)3(s) Precipitate is iron (III) hydroxide

* The precipitate changes colour because the Fe2+ ions are readily oxidised to brown Fe3+ ions

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Complex ions In solution, the ions of transition metals form complex ions Complex ions consist of a central metal ion surrounded by ligands. [A ligand is a molecule or ion which donates a pair of electrons to the central metal ion to form a coordinate bond.] [A coordinate bond is one in which one of the bonded atoms provides both electrons for the shared pair.] [The coordination number is the total number of coordinate bonds formed between a central metal ion and its ligands.]

[Fe(H2O)6]2+ Complex ion is Fe2+, ligands are H20, coordination number 6 common ligands.... Name of ligand Water Ammonia Thiocyanate Cyanide Chloride Hydroxide

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Formula :OH2 :NH3 :SCN:CN:Cl:OH-

Charge 0 0 -1 -1 -1 -1

multidentate ligands Bidentate ligand ligandss Some ligands are bidentate  Can donate two lone pairs of electrons to the central metal ion to form two coordinate bonds  Can form octahedral complexes

[Ni(NH2CH2CH2NH2)3]2+  Can show cis-trans isomerism

Ethanedioate ion

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A hexadentat hexadentatee ligand A hexadentate ligand has six lone pairs of electrons, each forming a coordinate bond to a metal ion in a complex ion. e.g. EDTA, used as a chelating agent (decreases concentration of metal ions in solutions by binding them to a complex)

 Detergent – binds to Ca and Mg ions to reduce water hardness  In foods – removes metal ions that might catalyse oxidation of product  Medical – Anti clotting and treats lead and mercury poisoning

isomers Optical isom ers Requirements  Complex with three molecules or ions of a bidentate ligand  Complex with two molecules or ions of a bidentate ligand, and two molecules or ions of a monodentate ligand  Complex with one hexadentate ligand  Octahedral They are non super-imposable mirror images of each other. They rotate plane-polarised light differently – one clockwise, other anti-clockwise. Mixture containing equal amounts of two isomers has no effect because rotations cancel out.

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Stereoisomerism [Stereoisomers are species with the same structural and molecular formula but a different arrangement of the atoms in space.] You should be familiar with cis-trans in organic molecules, but as seen earlier, transition ion complexes can show cis-trans isomerism as well. Requirements...  Octahedral – coordination number of 6 o two different ligands  four of one, two of another

 Coordination number of 4 o Square planar NOT tetrahedral shaped o two different ligands  two of one, two of another

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Ligand substitution [A ligand substitution reaction is one in which a ligand in a complex ion is replaced by another ligand.] Normally, water molecules in an aqueous solution of a complex ion are replaced by another ligand.

Copper (II) aq ioions ns and ammonia [Cu(H2O)6]2+(aq) + 4NH3(aq) ⇌ [Cu(NH3)4(H2O)2]2+(aq) +4H2O (l) Pale blue solution Deep blue solution 4 water ligands are replaced by 4 ammonia ligands. The product has six ligands in an octahedral complex ion. Copper-oxygen bonds are longer than copper-nitrogen bonds, so the shape is distorted octahedral.

hydrochloricc acid Copper (II) aq ioions ns and hydrochlori [Cu(H2O)6]2+(aq) + 4Cl- (aq) ⇌ [CuCl4]2-(aq) +6H2O (l) Pale blue solution Yellow solution The original complex has six ligands, but the product complex has only four. Because chloride ligands are larger than water ligands, so fewer can fit round the central metal ion. The shape is tetrahedral. Same thing happens with cobalt (II) ions, except the colour change is pink to blue. Layla Gerami

Stability constants [The stability constant is the equilibrium constant for an equilibrium existing between a transition metal ion surrounded by water ligands and the complex formed when the same ion has undergone a ligand substitution.] When chloride ions are added to an aqueous solution of some transition metal ions, an equilibrium is set up. [Co(H2O)6]2+(aq) + 4Cl-(aq) ⇌ [CoCl4]2-(aq) + 6H2O(l) An expression for Kc can be written for this reaction... but we use the term stability constant, Kstab rather than Kc. Kstab = Water has been left out. All species are aqueous (dissolved in water) so water is in such a large excess, and its concentration is pretty much constant. In this case, the units would be dm12mol-4. A large value of Kstab indicates the position of equilibrium lies to the right. Complex ions with high stability constants are more stable than those with lower values. Consider again: [Co(H2O)6]2+(aq) + 4Cl-(aq) ⇌ [CoCl4]2-(aq) + 6H2O(l) At RTP, the equilibrium mixture contained ... 1.17 x 10-5 moldm-3 [Co(H2O)6]2+ and 0.800 moldm-3 Cl-. Kstab = 4.17 x 105 dm12mol-4 * 4.17 x 105 =

= 2.00 moldm-3 * The Kstab value is large, due to an increase in entropy, from a bigger number of moles. Layla Gerami

real life applications Transition metal complexes in mmedicine edicine Cis-platin is one of the most effective drugs against many forms of cancer. It is the cis-isomer of a platinum complex, [PtCl2(NH3)2].

It acts by binding to the DNA of fast-growing cancer cells. This alters their DNA and they are prevented from reproducing. Eventually, programmed cell death (apoptosis) occurs in those cells. Unfortunately, it comes with some side effects. A new generation of compounds with lower doses and less side effects have been developed, including carboplatin.

Haemoglobi Haemoglobinn Haemoglobin is found in red blood cells. Its job is to transport oxygen from the lungs around the body, and to pick up waste CO2 from the body to take to the lungs to be expelled. It is made from two parts – haem and globin.  Haem is a non protein molecule complex that can bind to Fe2+ ions. o It forms 4 dative covalent bonds o It binds in a square planar arrangement. o Allows two further dative covalent bonds- one above and one below  Globin is made from 4 proteins joined together in a polypeptide o They are optical isomers of each other o Each protein forms a dative covalent bond to the Fe2+ o Allows one area free for a dative covalent bond

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Haemoglobi Haemoglobinn cont.

 A haem complex forms a further dative covalent bond with one of the globin proteins  A space is left for a further dative covalent bond o This is where oxygen binds to be transported around the body  It can also form a complex with CO2 which is transported to the lungs.

Carbon monoxide- the silent killer?! Carbon monoxide can also bind to haemoglobin, like oxygen does. However, haemoglobin is said to have a higher affinity for CO than for O2. This means CO bonds more strongly to the haemoglobin than oxygen.  If CO is present, less haemoglobin will be available to bond to oxygen molecules.  Tissues will be starved of essential oxygen, needed for respiration.  This reaction is an example of ligand substitution – CO molecules can replace O2 molecules in haemoglobin. o Even worse is that this substitution is irreversible. o Oxygen can no longer ever bind to that haem site. Carbon monoxide is formed from the incomplete combustion of organic fuels. It is colourless and odourless so it is impossible to tell if its in the air. There are CO sensors available to give a warning of the silent killer. Symptoms of CO poisoning are headaches, nausea and suffocation. Eventually, death. CO is also formed when tobacco is burnt, which is why smokers can become short of breath.

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Specification ticksheet (a) deduce the electron configurations of atoms and ions of the d-block elements of Period 4 (Sc–Zn), given the atomic number and charge; ☑ (b) describe the elements Ti–Cu as transition elements, ie d-block elements that have an ion with an incomplete d sub-shell; ☑ (c) illustrate: ☑ (i) the existence of more than one oxidation state for each element in its compounds, (ii) the formation of coloured ions, (iii) the catalytic behaviour of the elements and/or their compounds; (d) describe, including ionic equations, the simple precipitation reactions and the accompanying colour changes of Cu2+(aq), Co2+(aq), Fe2+(aq) and Fe3+(aq) with aqueous sodium hydroxide; ☑ (e) explain the term ligand in terms of coordinate bonding; ☑ (f) state and use the terms complex ion and coordination number; ☑ (g) state and give examples of complexes with sixfold coordination with an octahedral shape; ☑ (h) explain and use the term bidentate ligand ☑ (i) describe the types of stereoisomerism shown by complexes, including those associated with bidentate and multidentate ligands: ☑ (i) cis-trans isomerism (ii) optical isomerism (j) describe the use of cis-platin as an anticancer drug and its action by binding to DNA in cancer cells, preventing division; ☑ (k) describe the process of ligand substitution and the accompanying colour changes in the formation of: ☑ (i) [Cu(NH3)4(H2O)2]2+ and [CuCl4]2– from [Cu(H2O)6]2+, (ii) [CoCl4]2– from [Co(H2O)6]2+; (l) explain the biochemical importance of iron in haemoglobin, including ligand substitution involving O2 and CO; ☑ (m) state that the stability constant, Kstab,, of a complex ion is the equilibrium constant for the formation of the complex ion in a solvent from its constituent ions; ☑ (n) deduce expressions for the stability constant, Kstab, of a ligand substitution ☑ (o) relate ligand substitution reactions of complexes to stability constants and understand that a large Kstab results in formation of a stable complex ion; ☑ ALL INFORMATION IS FROM OCR CHEMISTRY A2 TEXTBOOK BY DAVE GENT AND ROB RITCHIE AND SOMETIMES MY OWN KNOWLEDGE 

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