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1 of 33 © Boardworks Ltd 2010 2 of 33 © Boardworks Ltd 2010 What is a transition metal? The d block elements are found in the centre of the periodic table. As you move across the d block, five d orbitals are filled, up to a total of ten electrons. Transition metals are d block elements that can form at least one stable ion with an incomplete d sub-level. Transition metals have typical metal properties, such as conducting heat and electricity, and high melting and boiling points. They are sonorous, ductile, malleable and lustrous. 3 of 33 © Boardworks Ltd 2010 Electron configurations 4 of 33 © Boardworks Ltd 2010 Evidence of electronic structure Successive ionization energies can be used to determine the electronic structure of an element. In a transition metal, electrons are initially removed from the 4s sub-level and then the 3d sub-level. There is only a small energy difference between these sub-levels. When both sub-levels are empty, the 4s sub-level is slightly lower in energy and is filled first. 5 of 33 © Boardworks Ltd 2010 Successive ionization energies 6 of 33 © Boardworks Ltd 2010 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 1s22s22p63s23p63d24s2 Ti2+ 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. 7 of 33 © Boardworks Ltd 2010 d-block elements or transition metals? A d block element has its highest energy electron in its d sub-level. A transition metal is a d block element which has a partially filled d sub-level in at least one stable ion. Scandium makes a stable Sc3+ ion with an electronic configuration of [Ar] 3d0 4s0 and is therefore not a transition metal. 8 of 33 Zinc makes a stable Zn2+ ion with an electronic configuration of [Ar] 3d10 4s0 and is therefore not a transition metal. © Boardworks Ltd 2010 d block elements vs transition metals 9 of 33 © Boardworks Ltd 2010 10 of 33 © Boardworks Ltd 2010 Variable oxidation states Transition metals can form a number of stable ions, each with the metal in a different oxidation state. Variable oxidation states are possible because the 4s and 3d sub-levels are very close in energy. It is relatively easy to lose electrons from either of these sub-levels. The oxidation state of the metal in a compound is noted as a Roman numeral after the name of the metal. Iron(II) means that the compound contains Fe2+, whereas iron(III) contains Fe3+. 11 of 33 © Boardworks Ltd 2010 Identify the oxidation states 12 of 33 © Boardworks Ltd 2010 Oxidation states of vanadium 13 of 33 © Boardworks Ltd 2010 Oxidation states and bonding At lower oxidation states, transition metals form ionic bonds. At higher oxidation states, transition metals cannot form monatomic ions. Instead they bond covalently to form compounds or molecular ions. For example, manganese forms ionic bonds in manganese(II) chloride and covalent bonds in the MnO4– oxoanion. Transition metals are often in their highest oxidation state when bonded to very electronegative elements like oxygen and fluorine. 14 of 33 © Boardworks Ltd 2010 Common oxidation states 15 of 33 © Boardworks Ltd 2010 16 of 33 © Boardworks Ltd 2010 Ligands 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 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. 17 of 33 The lone pair of electrons on the oxygen can be donated into the partially filled d sub-level of the transition metal. © Boardworks Ltd 2010 Bidentate ligands Bidentate ligands contain two atoms that donate pairs of electrons to form coordinate bonds. For example: Ethane-1,2-diamine (en) 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. 18 of 33 © Boardworks Ltd 2010 Multidentate ligands Multidentate ligands contain more than two atoms that donate pairs of electrons to form coordinate bonds. 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. 19 of 33 © Boardworks Ltd 2010 Bonding atoms in ligands 20 of 33 © Boardworks Ltd 2010 Identifying ligands 21 of 33 © Boardworks Ltd 2010 Coordination number 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. Hexaaquacopper(II) Coordination number = 6 22 of 33 Tetrachlorocobalt(II) Coordination number = 4 © Boardworks Ltd 2010 What is a complex? 23 of 33 © Boardworks Ltd 2010 Identify the complex ion 24 of 33 © Boardworks Ltd 2010 Shapes of complex ions 25 of 33 © Boardworks Ltd 2010 Cis–trans isomerism Stereoisomerism is where molecules have the same molecular formula, but a different arrangement of atoms in space. Cis–trans isomerism occurs because the ligands cannot rotate around the central metal ion. cisplatin transplatin Different stereoisomers can have different chemical properties. Cisplatin is an isomer that is used as an anticancer drug. The trans isomer, transplatin, has no known medical use. 26 of 33 © Boardworks Ltd 2010 Optical isomerism Another form of stereoisomerism is optical isomerism, in which a molecule can exist as two forms that are nonsuperimposable mirror images of each other, just like a left hand and right hand. 27 of 33 © Boardworks Ltd 2010 Transition metal complexes 28 of 33 © Boardworks Ltd 2010 Identify the complex shape 29 of 33 © Boardworks Ltd 2010 30 of 33 © Boardworks Ltd 2010 Glossary 31 of 33 © Boardworks Ltd 2010 What’s the keyword? 32 of 33 © Boardworks Ltd 2010 Multiple-choice quiz 33 of 33 © Boardworks Ltd 2010