IB Chemistry: First row d-block Elements First Row d-block Elements List the characteristic properties of transition elements ● Transition metals form : ○ Colored compounds ○ Complex ions ● Transition metals can exist in Variable Oxidation states ● Transition Metals can often act as catalysts to reactions In the exam, they might ask you to list a few properties of transition metals, or ask you to compare transition metals with Group I metals. Above are the weapons you need :D. Explain why Sc and Zn are not considered to be transition elements. Any element with an incomplete d sublevel in one or more of its oxidation states is referred to as a transition metal element. ● Scandium is not considered to be a typical transition metal as Sc3+ has no d electrons. ● Zinc isn’t a transition metal as it contains a full d sub level in all of its oxidation states. Explain the existence of variable oxidation number in ions of transition elements. 3d and 4s sub-shells are similar in energy. When transition metals lose electrons, the 4s electrons are lost first. All transition metals have at least an oxidation state of 2+. Some of them can form 3+ or 4+ ions as the ionization energies are such that up to two d electrons can be lost. The maximum stable oxidation state would be the loss of all available bonding electrons. Mn (3d54s2 ) → Mn 7+ (AR) Define the term ligand A ligand is neutral molecule or anion which contain a non-bonding pair of electrons. These electrons pair can then form co-ordinate covalent bonds with the metal ion to form complex ions. Describe and explain the formation of complexes of d-block elements. A complex is formed when ligands datively covalently bond to a central transition metal ion (or atom) by donating a pair of electrons. (Regular covalent bonds involve sharing electrons equally from each atom).
● Fe3+ + 6H2 O → [Fe(H 2O)6] 3+ ● Fe3+ + 6CN → [Fe(CN) 6] 3- ● [Cu(H2O)6] 2+ + 4Cl– → [CuCl 4]2-+6H2O ● Ag+ +2NH3 →[Ag(NH 3)2]+ 13.2.6 Explain why some complexes of d-block elements are coloured In complexes of d-block elements, the d-orbitals are split into two distinct levels. The energy levels between these two wavelengths correspond to a particular wavelength or frequency inthe visible region of the spectrum. When light falls on the complex, energy of a particular wavelength is absorbed and electrons are excited from the lower level to the higher level. They split The amount of splitting depend on the nature of the transition metal, the oxidation state, the shape, the nature of the ligand, and this explains for why different complexes form different colors. State examples of the catalytic action of transition elements and their compounds. ● Iron in the Haber Process ● Vanadium oxide (V) in the Contact Process ● Nickel in Hydrogenation Reactions ● Manganese (IV) Oxide with hydrogen peroxide. Outline the economic significance of catalysts in the Contact and Haber processes Adding catalysts reduces the activation energy of both the forward and reverse reaction equally at equilibrium – so you will NOT have an increased yield. So why add them? Because the time to reach equilibrium is reduced and only when equilibrium has occurred can Le Chatelier’s principle be used to manipulate it to make more of what you want to sell ! This idea is further explored in unit 7.