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Topic 13.1 First Row d-Block Elements Assessment Statements 13.2.1 List the Characteristic properties of transition elements 13.2.2 Explain why Sc and Zn are not considered transition elements 13.2.3 Explain the existence of variable oxidation number in ions of transition elements. 13.2.4 Define the term ligand. 13.2.5 Describe and explain the formation of complexes of dblock elements. 13.2.6 Explain why some complexes of d-block elements are coloured. 13.2.7 State examples of the catalytic action of transition elements and their compounds. 13.2.8 Outline the economic significance of catalysts in the contact and Haber Process Assessment Statements 13.2.1 List the Characteristic properties of transition elements Where are the transition metals? The transition metals are the block of elements located between group 2 and group 3 of the periodic table. group 2 group 3 Sc Ti V Cr Mn Fe Co Ni Cu Zn Y Zr Nb Mo Tc Ru Rh Pd Ag Cd La Hf Ta W Re Os Ir Pt Au Hg Ac Rf Db Sg Bh Hs Mt Ds Rg ? Here, the word ‘transition’ is used to mean ‘in-between’. What are the transition metals? Why are they called the ‘typical metals’? There are over 30 transition metals. They include most of the metals we are familiar with and use everyday, such as iron, copper and gold. However, there are many transition metals that are less familiar to us, because they are very rare or have few uses. The transition metals are known as ‘typical’ metals. Why do you think this might be? What are the properties of the transition metals? The transition metals are known as ‘typical’ metals because of their physical properties. They are: lustrous (bright and shiny). hard and strong. high density. malleable (can be bent and pressed into different shapes) and ductile (can be drawn into wires). good conductors of heat and electricity. high melting and boiling points (except mercury, which is liquid at room temperature). How do the transition metals compare with the alkali metals? Comparing properties of different metals How do the properties of transition metals compare with those of alkali metals? Compared to the alkali metals, the transition metals: are harder and stronger. They cannot be cut with a knife. are more dense. This means that in a fixed volume of metal there are more atoms of a transition metal than there are of an alkali metal. have higher melting and boiling points – except mercury. 13.2 First row D-Block elements 3d spans from Scandium to Zinc Transition elements are a subset of the d-block that have a partially filled d-sublevel in one of its common oxidation states. Physical properties: 1 High electrical and thermal conductivity 2 High melting point 3 Malleable (easy beaten in shape) 4 High tensile strength (can hold large loads without breaking 5 Ductile (can be drawn easily into wires) Comparing densities of metals Comparing melting points of metals True or false? Other Properties (required for IB) Form coloured ions Form complexes Have variable oxidation states Show catalytic activity These will be explained in the following assessment statements Assessment Statements 13.2.2 Explain why Sc and Zn are not considered transition elements 13.2.3 Explain the existence of variable oxidation number in ions of transition elements. ==== Sc always forms 3+ ions, it loses all its valence electrons, 4s2 and 3d1. Cr and Cu have unusual electron configuration due the stability of half filled and filled 3d sublevel ==== Zn always forms 2+ ions, it loses the 4s2 electrons and keeps the 3d full. The metals in 3d can lose different amounts of electrons to form different ions. These ions are all said to be in different oxidation states. The oxidation state (oxidation number) is the same as the charge on the ion, ex. Cr3+ has an oxidation state of +3; Cr2+ has an oxidation state of +2. Sc and Zn don’t share all the properties of transition elements as they don’t have a partially filled d block. (they cannot form multiple ions) Oxidation state first row transition series (Memorize the red ones) Sc Ti V Cr Mn Fe Co Ni Cu Zn +1 +3 +2 +2 +2 +2 +2 +2 +2 +2 +3 +3 +3 +3 +3 +3 +3 +3 +4 +4 +4 +4 +4 +4 +4 +5 +5 +5 +5 +5 +6 +6 +6 +2 +7 Important notes! All metals show +2 and +3 the M3+are more stable from scandium to chromium, M2+ is more stable for the latter Oxidation states above +3 show more covalent character Compounds with higher oxidation state tend to be oxidizing agents (K2Cr2O7) Transition Metal Electronic Structures When transition metals form ions, the 4s electrons are removed before the 3d electrons. This means that nearly all of them make stable 2+ ions. Ti Ti2+ 1s22s22p63s23p63d24s2 1s22s22p63s23p63d24s0 Which Period 4 transition metals are likely to make stable 1+ ions? Chromium and copper because they lose the one electron from their 4s sub-level. Explanation of Variable Oxidation Number Transition Elements s-block metals lose s electrons easily but the ionization energies for the inner electrons are so high that these are never lost. For this reason they always have the same oxidation state - a +1 ion has oxidation number +1. (Mg, Ca , Al etc…) Ionization energy increases abruptly when all outer S electrons are removed. Element 1st IE 2nd IE 3rd IE 4th IE 5th IE 6th IE Ti 685 1310 2652 3564 11345 15643 V 759 1560 2955 4300 5400 12645 Ionization energies Titanium and Vanadium Ionization energy increases for Titanium and Vanadium is more gradual as the 3d and 4s orbitals are close in energy level Titanium shows oxidation state +2, +3, +4, (after that there is a large jump) no 5+ Vanadium shows oxidation state +2, +3, +4, +5 (after that there is a large jump) no 6+ Write the oxidation number in the brackets CrCl3 Cr2O72− • MnO2 • MnO4− • Fe2O3 • Cu2O chromium ( ) chloride dichromate ( ) ion manganese ( ) oxide permanganate ( ) ion iron ( ) oxide copper ( ) oxide Its time to wake up!!!!! Work out the oxidation state of the metal in each ion below. Vanadium VO4 3-, [VO(H2O)5]2+, [V(H2O)6]3+ Chromium CrO42- , [Cr(H2O)6]3+ Iron [Fe(H2O)6]3+ Transition Metal Compounds As most transition metals can form different ions, this means For example: they can form multiple compounds. Copper can form Cu+, which can make the red compound copper (I) oxide – Cu2O. Copper can also form Cu2+, which can make the black compound copper (II) oxide – CuO. The number in brackets indicates how many electrons have been lost. Transition Metal Compounds and Colour Most transition metals form coloured compounds. For example: Iron (II) oxide (FeO2) is black. Iron (III) oxide (Fe2O3) is red/brown – when hydrated this is rust. Copper (II) sulfate crystals (CuSO4.H2O) is blue – these can be turned white by heating the crystals to remove the water. Uses of Coloured TM Compounds The colour of many gemstones comes from the presence of transition metal compounds. For example, the gemstone jade contains iron. The coloured compounds of transition metals can also be used in many ways, for example: to colour stained glass windows to colour paints as coloured glazes on pottery. How are transition metal ions identified? The presence of transition metal ions in a solution can be tested by adding sodium hydroxide solution. If transition metal ions are present, a metal hydroxide is formed. This is insoluble and so appears as a solid called a precipitate. Different metal ions produce different coloured precipitates: Fe2+ ions produce a grey/green precipitate of Fe(OH)2 . Fe3+ ions produce an orange/ brown precipitate of Fe(OH)3 . Cu2+ ions produce a blue precipitate of Cu(OH)2 . Assessment Statements 13.2.4 Define the term ligand. 13.2.5 Describe and explain the formation of complexes of d-block elements. Coordinated Ligands Ligands are the molecules (or ions) which donate an electron pair to form a dative covalent bond with the central transition metal atom (forming a complex molecule or ion). A ligand is any atom, ion or molecule which can donate a pair of electrons to a metal ion. Ligands are Lewis bases and nucleophiles. Ligands Ligands are classified by the number of dative covalent or coordinate bonds that they can make. Water molecules frequently act as ligands. Each water molecule makes a single bond with the metal ion. Ligands which form single coordinate bonds are called unidentate or monodentate. The lone pair of electrons on the oxygen can be donated into the partially filled d sub-level of the transition metal. Bidentate ligands contain two atoms that donate pairs of electrons to form coordinate bonds. For example: Bidentate Ligands Ethane-1,2-diamine Both nitrogen atoms donate lone pairs to the metal ion. Ethanedioate ion The two single-bonded oxygen atoms both donate lone pairs to the metal ion. Multidentate ligands contain more than two atoms that donate pairs of electrons to form coordinate bonds. Multidentate ligands The EDTA4– ion forms six coordinate bonds with a metal ion. Lone pairs are donated by the four negatively-charged oxygen atoms and the two nitrogen atoms. The coordination number is the number of coordinate bonds to the metal ion. This is different to the oxidation state of the metal ion or complex. Coordination number Hexaaquacopper(II) Coordination number = 6 Tetrachlorocobalt(II) Coordination number = 4 Complexes Ligands The ions of d-block metals and those in the lower section of the p-block (like lead) have unfilled valence d and p orbitals. These orbitals can accept a lone pair of electrons from species, known as ligands, to form a dative covalent bond between the ligand and the metal ion. Ex. An NH3/H2O (ligands) molecule can donate its non-bonding electron pair to a Cu2+ ion. The number of dative or coordinate rents bonds from the ligands to the central ion is the coordination number: C. Coordination Number CN - Number of ligand atoms bonded directly to the central metal ion. Specific for given metal ion in particular Oxidation #. i.e., [Co(NH3)6]+ CN = 6 Ligand # = 6 [Ag(NH3)2]+ CN = 2 Ligand # = 2 [Co(en)3]+ CN = 6 Ligand # = 3 Geometry of Complex is related to CN. CN = 2 Linear CN= 4 CN = 5 Tetrahedral (d10) Sq Planar (d8) Trigonal bipyramidal Square Pyramide CN = 6 Octahedral F F Br F F I I I F P F F I I F F F Br F S F F F F Coordinated Complexes and Coordination Number Coord Number Shape 2 Linear [CuCl2]-, [Ag(NH3)2]+, [AuCl2]- 4 Square Planar [Ni(CN)4] 2-, [PdCl4]2[Pt(NH3)4] 2+, [Cu(NH3)4] 2+ Example F F Br F 4 Tetrahedral 6 Octahedral F [Cu(CN)4] 3-, [Zn(NH3)4]2+ [CdCl4] 2-, [MnCl4] 2- [Cu(H2O)6] 3+, [V(CN)6] 4-, [Cu(NH3)4Cl2] +, [Co(en)3] 3+ F F F S F F F Examples of some complex ions: Complex Ligand Coordinatio n number Oxidation number central ion shape [Fe(H2O)6]3+ H2O 6 3+ Octahedral [Co(NH3)6]3+ NH3 6 3+ Octahedral [CuCl4]- Cl- 4 2+ Tetrahedral [Ag(NH3)2]+ NH3 2 1+ Linear MnO4- O2- 4 2+ Tetrahedral PtCl2(NH3)2 Cl- and NH3 4 2+ Tetrahedral [Al(H20)]3+ H2O 6 3+ Octahedral The color of transition metal ion complexes If white light passes through the complex ion colored light is absorbed, electrons are excited to the higher d orbitals and the opposite color is seen. For example [Fe(H2O)6]3+ appears yellow because it’s ions absorb blue Assessment Statements 13.2.6 Explain why some complexes of d-block elements are coloured. Colour of ions When a colour change occurs in the reaction of a transition metal ion, there is a change in at least one of the following: Oxidation state Co-ordination number Ligand How do we see colour? Most transition metal compounds appear coloured. This is because they absorb energy corresponding to certain parts of the visible electromagnetic spectrum. The colour that is seen is made up of the parts of the visible spectrum that aren’t absorbed. For example, a red compound will absorb all frequencies of the spectrum apart from red light, which is transmitted. What happens when light is absorbed? In transition metal ions, the d sub-level is only partially filled. This means that electrons can move between d orbitals. In a transition metal complex, the relative energies of the d orbitals change. Electrons can be promoted to higher energy orbitals. For electrons to be promoted, they need to absorb light energy of a particular frequency. This frequency depends on the precise difference in energy between the d orbitals. Colors of transitional ions Sc 3+ Colorless Ti 3+ Violet V3+ Green Cr 3+ Violet Mn2+ Pink Fe3+ Yellow Co2+ pink Ni2+ Green Cui2+ Blue Zn2+ Colorless Note regarding Complex ions: The formation of complex ions stabilizes certain oxidation states. The formation of a complex ion can also affect the color of a metal ion in solution. For many complexes, ligand replacement can occur depending on which complex is more stable. Transition metals absorb light as the d orbital splits into two sublevels In an isolated atom all of the d sublevel electrons have the same energy. When ligands are attached to transition metal ions, the d orbitals may split into two groups. Some of the orbitals are at a lower energy than the others The difference in energy of these orbitals varies slightly with the nature of the ligand or ion surrounding the metal ion When white light passes ,light of a particular frequency is absorbed. The result is a colored compound it shows the complimentary color. Various oxidation states of Nickel (II) The colour of a transition metal compound is determined by the difference in energy between its d orbitals. Factors affecting colours This can be affected by several factors: size and type of ligands coordination number strength of metal–ligand bonds oxidation state. complex shape [Cr(H2O)6]3+ [Ni(H2O)6]2+ [Fe(H2O)6]2+ [Fe(H2O)6]3+ Colours of complexes A transition metal will appear different colours in complexes with different ligands. For example: [Cu(H2O)6]2+ [CuCl4]2– Transition Metals (ions) as Catalysts The colors of the ions and complex ions of d block elements depends on: 1 Nuclear charge hence identity central atom 2 Charge density of the ligand eg: NH3 has a higher charge density as H2O 3 Number of D electrons, hence charge 4 Shape of the complex Assessment Statements 13.2.7 State examples of the catalytic action of transition elements and their compounds. 13.2.8 Outline the economic significance of catalysts in the contact and Haber Process Catalysts A catalyst enables a reaction to happen by providing an alternative pathway with a lower activation energy. Many D block elements are catalysts for various chemical reactions. The transition metals form complex ions with ligands that can donate lone pairs of electrons. This results in close contact between the metal ion and the ligand. Heterogeneous (different state) catalysts are more common than homogeneous. A catalyst is a substance that speeds up reactions by providing an alternative reaction route with lower activation energy. Transition metals as catalysts Transition metals are good catalysts for two reasons: they show variable oxidation states. This allows them to act as intermediates in the exchange of electrons between reacting species. they provide a surface for reactions to occur. The metal forms weak bonds to the reacting species, holding them in place. Heterogeneous Catalyst Refers to the form of catalysis where the phase of the catalyst differs from that of the reactants. Phase here refers not only to solid, liquid, vs gas, but also immiscible liquids, e.g. oil and water. The great majority of practical heterogeneous catalysts are solids and the great majority of reactants are gases or liquids. Heterogeneous catalysis is of paramount importance in many areas of the chemical and energy industries. Heterogeneous catalysis has attracted Nobel prizes for Fritz Haber and Carl Bosch in 1918, Irving Langmuir in 1932, and Gerhard Ertl in 2007. There are two types of catalysts: homogeneous and heterogeneous. Types of catalysts Homogeneous catalysts are in the same phase as the reaction species, e.g. two miscible liquids. Heterogeneous catalysts are in a different phase to the reaction species, e.g. two immiscible liquids. Homogeneous Catalysis A sequence of reactions that involve a catalyst in the same phase as the reactants. Most commonly, a homogeneous catalyst is codissolved in a solvent with the reactants. Enzymes are homogeneous catalysts that are essential for life but are also harnessed for industrial processes. A well studied example carbonic anhydrase, which catalyzes the release of CO2 into the lungs from the blood stream Catalysts are often very expensive. Maximising the efficiency of catalysts minimizes the cost. One method of increasing efficiency is to increase the surface area of the catalyst. Improving Catalyst Efficiency In a catalytic converter, a ceramic honeycomb structure is coated with finely divided rhodium and platinum. The ceramic support medium is inert but it increases the surface area of the catalyst and reduces the amount needed. Some Common D Block Catalysts (heterogeneous) Examples of D block elements that are used as catalysts In a catalytic converter Decomposition of hydrogen peroxide Haber process: N2 + 3H2 <=> 2NH3 Removal 2CO + 2NO = 2CO2 + N2 : Most cars in the UK are fitted with catalytic converters. These convert pollutants such as carbon monoxide, nitrogen oxides and unburnt hydrocarbons into carbon dioxide, nitrogen and water; gases which are found naturally in our atmosphere. Catalytic converters Catalytic converters contain an inert honeycomb structure coated with the catalyst – platinum and rhodium. The exhaust gases enter through the holes and react on the catalyst surface. Catalytic converters are easily poisoned, especially by anti-knock additives. They do not work when cold and reduce fuel economy by 2-10%. Many industrial processes use heterogeneous catalysts. Catalysts increase the rate of a chemical reaction, although the equilibrium position is unchanged. The Haber Process The Haber Process produces ammonia from hydrogen and nitrogen gases. It uses a heterogeneous iron catalyst. iron catalyst N2(g) + 3H2(g) 2NH3(g) Over several years, the iron catalyst becomes poisoned by impurities such as sulfur compounds. When the efficiency of the catalyst is greatly reduced, it must be replaced. Sulfuric acid is produced by the Contact Process using a heterogeneous catalyst of vanadium(V) oxide. The Contact Process 2SO2 + O2 2SO3 There are two steps in the reaction. SO2 + V2O5 2V2O4 + O2 SO3 + V2O4 2V2O5 The oxidation number of vanadium changes from +5 to +4 to +5 again over the course of the reaction. Methanol is produced by two consecutive reactions. Producing Methanol Synthesis gas, a mixture of carbon monoxide and hydrogen, is first produced from the reaction of methane and steam. Step 1 CH4(g) + H2O(g) CO(g) + 3H2(g) This gas is then used to produce methanol. The reaction is sometimes catalysed by chromium(III) oxide, (Cr2O3). Step 2 CO(g) + 2H2(g) synthesis gas CH3OH(g) methanol Ions of transition metals a s homogeneous Catalysts Fe2+ in heme , oxygen is transported and forms a weak bond with the heme group (central ion in heme) is Fe2+ Co3+ in vitamin B12, part of the vitamin B12 consist of octahedral CO3+ Vitamin B12 is used for the production of blood Spot the uses of the transition metals How many everyday uses of transition metals can you see? What are the uses of the transition metals? activity The lenses of polychromic sunglasses contain silver halide nanoparticles. These particles are transparent in artificial light. A photochemical reaction occurs on exposure to UV radiation, found in sunlight. Polychromic Sunglasses UV radiation changes the shape of the nanoparticles. They absorb some of the visible light, so the lenses appear darker. Without UV radiation, the molecules return to their original shape and the lenses appear colourless again. Glass blocks the UV light responsible for this reaction, so polychromic lenses will not darken in a car or when looking out of a window. Platin is a platinum complex that forms cis–trans stereoisomers. The cis isomer, cisplatin, is used as an anti-cancer drug. The trans isomer, transplatin, doesn't have the same effect and is not used in chemotherapy. Chemotherapy Drugs cisplatin transplatin Cisplatin is administered intravenously. It is very useful in treating solid tumours. How Does Cisplatin Act? For a cell to replicate, the double helix DNA molecule must unwind. Cisplatin prevents it from unwinding by forming coordinate bonds with the DNA bases. Nitrogen atoms in the bases displace the ammonia ligands in the cisplatin complex. Cisplatin is an important drug used to prolong the life of cancer patients. However, there are some risks associated with its usage. Risks of Cisplatin Cisplatin also prevents normal cells in the body from replicating. Patients may experience sideeffects, ranging from nausea and vomiting to life-threatening complications such as kidney damage. Patients can become resistant to cisplatin. Most transition metal compounds are coloured and many are used in paints and dyes. Paints and Dyes Copper compounds produce very vibrant blue colours. Phthalocyanine blue is a copper complex used in paint dyes. It is very stable and insoluble in water. Titanium dioxide is a white solid at room temperature. Nanoparticles of titanium oxide are used to whiten paper and as a white pigment in paint. An alloy is a solid mixture of two or more metals, that can also contain other non-metal elements. Alloys often have properties that are very different to their constituent metals. Alloys Carbon is added to iron to make an alloy of steel, which is much stronger than iron. Chromium can also be added to make stainless steel, which is resistant to corrosion. Copper is used in many different alloys, such as brass, bronze and coinage metals. The copper content of an alloy can be estimated by titration with I2/S2O32–.