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TOPIC 13 THE PERIODIC TABLE – THE TRANSITION METALS 13.1 FIRST ROW D-BLOCK ELEMENTS ESSENTIAL IDEA The transition elements have characteristic properties; these properties are related to their all having incomplete d sublevels. NATURE OF SCIENCE (3.1) Looking for trends and discrepancies – transition elements follow certain patterns of behavior. The elements Zn, Cr and Cu do not follow these patterns and are therefore considered anomalous in the first row d-block. INTERNATIONAL-MINDEDNESS The properties and uses of the transition metals make them important international commodities. Mining for precious metals is a major factor in the economies of some countries. THEORY OF KNOWLEDGE The medical symbols for female and male originate from the alchemical symbols for copper and iron. What role has the pseudoscience of alchemy played in the development of modern science? UNDERSTANDING/KEY IDEA 13.1.A Transition elements have variable oxidation states, form complex ions with ligands, have colored compounds, and display catalytic and magnetic properties. d-block elements Screencast by Iwanowski To many people, the d-block elements are the typical metals such as iron and copper. The 10 elements of the first row of dblock elements have similar chemical and physical properties. These 10 elements show a “lull” in the periodic patterns that we have seen in the s and p block elements. The similarity in properties of the first row dblock elements is illustrated by the small range in atomic radii. The small decrease in atomic radii is due to the fact that the outer 4s electrons experience only a small increase in nuclear charge. The expected increase in nuclear charge due to each added proton is offset by the addition of electrons to the inner 3-d sub level. This small increase in radii also accounts for the small increase in 1st ionization energies across the first transition elements. Element Core electrons 3d electrons 4s electrons Sc [Ar] 3d1 4s2 Ti [Ar] 3d2 4s2 V [Ar] 3d3 4s2 Cr [Ar] 3d5 4s1 Mn [Ar] 3d5 4s2 Fe [Ar] 3d6 4s2 Co [Ar] 3d7 4s2 Ni [Ar] 3d8 4s2 Cu [Ar] 3d10 4s1 Zn [Ar] 3d10 4s2 Remember that Cr and Cu are electron configuration exceptions. They prefer having half-filled and filled d-orbitals to be more stable. The characteristic properties of transition elements. High electrical and thermal conductivity High melting point Malleable – easily beaten into shape High tensile strength – can hold large loads without breaking Ductile – easily drawn into wires ◦ These properties are explained by strong metallic bonding. The 3d and 4s electrons are close in energy and are all part of the delocalized sea of electrons which holds the metal lattice together. PHYSICAL PROPERTIES With the exception of Zn, the 3d elements are transition metals. ◦ They form compounds with more than one oxidation number. ◦ They form a variety of complex ions. ◦ They form colored compounds. ◦ They act as catalysts when either elements or compounds. ◦ They have magnetic properties. CHEMICAL PROPERTIES A catalyst is a substance which alters the rate of a reaction by providing an alternative reaction pathway with a lower activation energy. Catalysts play an essential role in the chemical industry as they allow chemical processes to proceed at an economical rate. TRANSITION METALS AS CATALYSTS A heterogeneous catalyst is in a different state of matter than the reactants. ◦ For example the reactants may be gases and the catalyst a solid. The ability of transition elements to use the 3d and 4s electrons to form weak bonds to small reactant molecules makes them effective heterogeneous catalysts as they provide a surface for the reactant molecules to come together with the correct orientation. HETEROGENEOUS CATALYSTS Homogeneous catalysts are in the same state of matter as the reactants. The ability of transition metals to show variable oxidation states allows them to be very effective homogeneous catalysts in redox reactions. Homogeneous catalysts are of fundamental biological importance. HOMOGENEOUS CATALYSTS UNDERSTANDING/KEY IDEA 13.1.B Zn is not considered to be a transition element as it does not form ions with incomplete d-orbitals. Transition elements form one or more ions with a partially filled d sub-level. Zinc only forms one ion and it does NOT have a partially filled d sub-level. Zn makes the Zn2+ ion which has the electron configuration of [Ar]3d10. Zinc does not make colored compounds. UNDERSTANDING/KEY IDEA 13.1.C Transition elements show an oxidation state of +2 when the “s” electrons are removed. When the first row d-block elements form ions, they ALWAYS lose the 4s electrons first to make the 2+ ions. To make ions of higher than 2+, they start losing the 3d electrons. APPLICATION/SKILLS Be able to explain the ability of the transition metals to form variable oxidation states from successive ionization energies. The s block elements only show one oxidation state corresponding to its group number. Li makes Li+1 and Ca makes Ca+2. The transition elements show more than one oxidation state and these states are related to patterns in successive ionization energies. ◦ Remember that ionization energy is the energy needed to remove the outermost electron. VARIABLE OXIDATION NUMBERS Because the 3d and 4s orbitals are close in energy, the electrons can be removed without a huge jump in energy as you would see from the s and p orbitals. Consider the 2 examples: ◦ Ca: 1s22s22p63s23p64s2 ◦ Ti: 1s22s22p63s23p63d24s2 ◦ Calcium will lose the 4s2 electrons and then it would take a huge amount of energy to pull off the electrons in the 3p orbital. ◦ Titanium will lose the 4s2 electrons to make Ti+2, then one of the 3d electrons to make Ti+3, then the other 3d electron to make Ti+4. It does not make a +5 ion because it takes too much energy to pull off the p electrons. 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 Be familiar with the oxidation states listed in red. COMMON OXIDATION STATES Note that all transition elements show the +2 and +3 states. The M3+ ion is more stable from Sc to Cr, but the M2+ ion is more stable from Mn to Cu. ◦ This is due to the increased nuclear charge of the later elements making it more difficult to remove a 3rd electron. The maximum oxidation states increases in steps of +1 until Mn (due to the use of 4s and 3d electrons). After Mn, the number of states decreases by steps of -1. IMPORTANT ITEMS TO NOTE Oxidation states above +3 generally show covalent character. Compounds with higher oxidation states tend to be oxidizing agents. APPLICATION/SKILLS Be able to explain the nature of the coordinate bond within a complex ion. Complex Ions Key Terms - Iwanowski A complex ion is formed when a central ion is surrounded by molecules or ions which possess a lone pair of electrons. The relatively high charge and small size of the transition metal allows them to attract the ligand’s lone pair of electrons. These “ligands” are attached via a coordinate bond. ◦ A coordinate bond uses a lone pair of electrons to form a covalent bond. ◦ A ligand is a species that uses a lone pair of electrons to form a coordinate bond with a metal ion. The number of coordinate bonds from the ligands to the central ion is called the coordination number. There are four main shapes of complex ions: ◦ ◦ ◦ ◦ Linear – coordination number of 2 Square planar – coordination number of 4 Tetrahedral – coordination number of 4 Octahedral – coordination number of 6 APPLICATION/SKILLS Be able to deduce the total charge given the formula of the ion and ligands present. Some examples of complex ions: ◦ ◦ ◦ ◦ ◦ [Fe(H2O)6]3+ [Co(NH3)6]3+ [CuCl4]2[Ag(NH3)2]+ PtCl2(NH3)2 Can Can Can Can you you you you identify the ligand? tell the coordination number? give the shape? tell the charge on the metal ion? Complex Ligand Coordination Number Oxidation # of central ion Shape [Fe(H2O)6]3+ H2O 6 +3 octahedral [Co(NH3)6]3+ NH3 6 +3 octahedral [CuCl4]2- Cl- 4 +2 tetrahedral [Al(OH)4(H2O)2]- OH- 4 +3 octahedral [Fe(CN)6]3- CN- 6 +3 octahedral [Ag(NH3)2]+ NH3 2 +1 linear MnO4- O2- 4 +7 tetrahedral Ni(CO)4 CO 4 0 tetrahedral PtCl2(NH3)2 Cl- and NH3 4 +2 sq planar COMPLEX ION EXAMPLES APPLICATION/SKILLS Be able to explain the magnetic properties in transition metals in terms of unpaired electrons. Screencast – Magnetism – UCLA Physics Every spinning electron in an atom or molecule can behave as a tiny magnet. Electrons with opposite spins have opposing orientation so have no net magnetic effect. Elements and ions with paired electrons do not show magnetic properties. If elements or ions have unpaired electrons, they will show magnetic properties. MAGNETIC PROPERTIES Diamagnetism – property of all materials, all electrons are paired, show weak opposition to an applied magnetic field Paramagnetism – only occurs with substances with unpaired electrons, the magnetism is proportional to the applied field and in the same direction Ferromagnetism – only occurs with long range ordering of the unpaired electrons, magnetism can be greater than the applied field. Iron, cobalt and nickel are ferromagnetic. The unpaired d electrons in large numbers of atoms line up with parallel spins in regions called domains. These domains can become ordered if exposed to an external magnetic field. The magnetism can remain after the magnetic field is removed. Transition metal complexes with unpaired electrons show paramagnetic properties as they are pulled into a magnetic field. Paramagnetism increases with the number of unpaired electrons so generally increases from left to right across the Periodic Table until Chromium and then it decreases. Zinc is diamagnetic because it has no unpaired electrons. GUIDANCE Common oxidation numbers of the transition metal ions are listed in the data booklet on pages 9 and 14. Citations International Baccalaureate Organization. Chemistry Guide, First assessment 2016. Updated 2015. Brown, Catrin, and Mike Ford. Higher Level Chemistry. 2nd ed. N.p.: Pearson Baccalaureate, 2014. Print. Most of the information found in this power point comes directly from this textbook. The power point has been made to directly complement the Higher Level Chemistry textbook by Catrin and Brown and is used for direct instructional purposes only.