Transition+Metals

Transition metals (d-block elements)
lie in groups 3 - 12 of the periodic table. In the first transition series (Sc - Zn) the **3d shell is being filled **

Almost all the properties of the transition elements are related to their electronic structures and the relative energy levels of the orbitals available for their electrons.

=Characteristic Properties of Transition Elements =
 * 1) 1. Transition Elements are **all metals** - In the absence of a surface oxide coating they have a metallic lustre; high m.ps and b.ps, and are good conductors of heat and electricity. Most are grey/silver in colour, although copper is a pink metal. Like other metals they are usually malleable, ductile and sonorous.

2**. Size, Electronegativity and Ionisation Energy.** Because the electrons are being added to the inner 3//d//-subshell, there is only a very small decrease in size across the first transition row. Similarly there is only a marginal increase in electronegativity and ionisation energy.

3. **Variety of Oxidation State** In the first row of //d//-block elements, both the 3//d// and 4//s// electrons can be considered as part of the valence shell. In forming ions these elements lose the 4//s// electrons and a variable number of 3//d// electrons. This means the elements show variable valence. It is this ability of the transition elements to use at least some of the underlying //d// electrons in bonding which makes much of transition element chemistry distinctive.

This ability to have a variety of oxidation states applies to all the transition elements of the first row with the exception of Sc and Zn. The scandium atom has electron configuration [Ar] 3//d//14//s//2 so only has one electron to lose from the 3//d// level. This means the maximum charge on a scandium ion is +3 (Sc3+). The zinc atom does not behave as a typical transition metal atom as its electron structure [Ar] 3//d//104//s//2 means it only forms the Zn2+ ion by losing the 2 electrons from the 4//s// level, leaving a stable full 3//d// sublevel.

The number of oxidation states generally increases with the number of unpaired electrons, with elements in the middle of the row (eg. Mn) having the widest range of oxidation states. The maximum oxidation state for transition elements up to Mn is equal to the total number of valence electrons available.

Element V Cr Mn Fe Cu Electrons 3//d//34//s//2 3//d//54//s//1 3//d//54//s//2 3//d//64//s//2 3//d//104//s//1 Ox. States +2 to +5 +2 to +6 +2 to +7 +2, +3 +1, +2 Because of the variety of oxidation states available, transition elements are involved in many **redox** reactions. Species in which an element is in a high oxidation state (MnO4 // - //<span style="font-family: Arial,sans-serif; font-size: 11pt;">, ox state +7, Cr2O72 // - //<span style="font-family: Arial,sans-serif; font-size: 11pt;">, ox state +6) tend to be good oxidising agents. Conversely, some species in which the element has a low oxidation state eg. Fe2+, or the metals themselves, are good reductants.

<span style="font-family: Arial,sans-serif; font-size: 11pt;">4. **Bonding - Ionic to Covalent** <span style="font-family: Arial,sans-serif; font-size: 11pt;">When the transition elements are in low oxidation states (+2, +3) they exist as monatomic ions in ionic compounds e.g. manganese(II) chloride (MnCl2) and copper(II) nitrate (Cu(NO3)2). Compounds with transition elements in oxidation states higher than +3 generally have the transition elements covalently bound in polyatomic ions such as dichromate Cr2O72 // - //<span style="font-family: Arial,sans-serif; font-size: 11pt;"> and permanganate MnO4 // - //<span style="font-family: Arial,sans-serif; font-size: 11pt;">.

<span style="font-family: Arial,sans-serif; font-size: 11pt;">5. **Coloured Compounds and** Complex ions.
<span style="font-family: Arial,sans-serif; font-size: 11pt;"> <span style="font-family: Arial,sans-serif; font-size: 11pt;">The compounds of transition elements are usually coloured due to the partially filled //d// orbitals and the ability to excite electrons into a higher energy level by absorption of visible light. The magnitude of the energy absorbed and the resulting colour depends on the nature of any ligands attached to the metal ion eg most Cu2+ salts are blue but CuCO3 is green and both CuS and CuO are black. The colouring in most ceramics and precious stones are the result of transition metal oxides.

<span style="font-family: Arial,sans-serif; font-size: 11pt;">Zn2+ compounds, with the electron arrangement [Ar]3//d//10, have no vacant 3//d// orbitals and these compounds are therefore white. Similarly Sc3+ compounds are white because they do not have any //d// electrons.

<span style="font-family: Arial,sans-serif; font-size: 11pt;">Manganese <span style="font-family: Arial,sans-serif; font-size: 11pt;">Mn is an important component of alloys. In steel it increases the hardness, toughness and resistance to abrasion. Mn exhibits all oxidation states from II to VII. The most stable oxidation states are +2, +4, and +7. The most common compound is manganese dioxide, MnO2. The permanganate ion, MnO4 - <span style="font-family: Arial,sans-serif; font-size: 11pt;">, is purple and is a strong oxidising agent (especially in acid solution).
 * <span style="font-family: Arial,sans-serif;">Chemistry ****<span style="font-family: Arial,sans-serif;"> of Individual Transition metals **

<span style="font-family: Arial,sans-serif; font-size: 11pt;">The reduction product of MnO4- depends on the pH of the solution. <span style="font-family: Arial,sans-serif; font-size: 11pt;">**MnO4** - --> **<span style="font-family: Arial,sans-serif; font-size: 15px;">Mn2+ **<span style="font-family: Arial,sans-serif; font-size: 15px;"> (Pink)

<span style="font-family: Arial,sans-serif; font-size: 15px; line-height: 22px;">(in acid conditions)

<span style="font-family: Arial,sans-serif; font-size: 11pt;">**MnO4** - --> **<span style="font-family: Arial,sans-serif; font-size: 15px;">MnO2 (Brown) **

(in Neutral Conditions)

<span style="font-family: Arial,sans-serif; font-size: 11pt;">**MnO4** - --> <span style="font-family: Arial,sans-serif; font-size: 11pt;">**MnO42** -

<span style="font-family: Arial,sans-serif; font-size: 11pt;">acid neutral or strongly <span style="font-family: Arial,sans-serif; font-size: 11pt;"> mildly alkaline alkaline

<span style="font-family: Arial,sans-serif; font-size: 11pt;"> pale pink or brown solid green ion <span style="font-family: Arial,sans-serif; font-size: 11pt;"> colourless

<span style="font-family: Arial,sans-serif; font-size: 11pt;">Chromium is a bright, lustrous, corrosion resistant metal. Emeralds and rubies owe their colour to traces of chromium compounds. Cr is used in stainless steel (about 15% Cr) and for chrome plating. <span style="font-family: Arial,sans-serif; font-size: 11pt;">The oxides of Cr vary from basic through amphoteric to acidic. //<span style="font-family: Arial,sans-serif; font-size: 11pt;">Basic //<span style="font-family: Arial,sans-serif; font-size: 11pt;"> CrO (low ox state, +2) – dissolves in acid to form Cr2+ ions in solution. //<span style="font-family: Arial,sans-serif; font-size: 11pt;">Amphoteric // <span style="font-family: Arial,sans-serif; font-size: 11pt;">Cr2O3 (ox state +3)-like Cr(OH)3 dissolves in both acid (to form Cr3+ ions in solution) and base (to form Cr(OH)4 - <span style="font-family: Arial,sans-serif; font-size: 11pt;">). //<span style="font-family: Arial,sans-serif; font-size: 11pt;">Acidic //<span style="font-family: Arial,sans-serif; font-size: 11pt;">CrO3 (high ox state +6) – dissolves in water to form acidic solution of chromic acid, H2CrO4. This chromic acid in turn gives rise two types of salt - the yellow chromates (containing the CrO42 - <span style="font-family: Arial,sans-serif; font-size: 11pt;">ion in basic solution) and orange dichromates (containing the Cr2O72 - <span style="font-family: Arial,sans-serif; font-size: 11pt;">ion in acidic solution). Both these oxyanions contain Cr in the +6 oxidation state. The equilibrium between these two anions is **NOT** a redox reaction but an example of an acid-base equilibrium. The ion present in an aqueous solution depends on the pH.
 * <span style="font-family: Arial,sans-serif; font-size: 11pt;">Chromium **

<span style="font-family: Arial,sans-serif; font-size: 11pt;"> 2CrO42 - <span style="font-family: Arial,sans-serif; font-size: 11pt;">+ 2H+ <span style="font-family: Arial,sans-serif; font-size: 11pt;"> Cr2O72 - <span style="font-family: Arial,sans-serif; font-size: 11pt;">+ H2O <span style="font-family: Arial,sans-serif; font-size: 11pt;"> yellow –present in alkaline soln orange – present in acid soln

=<span style="font-family: Arial,sans-serif; font-size: 11pt;">Vanadium, V = <span style="font-family: Arial,sans-serif; font-size: 11pt;">Vanadium is a soft, grey metal produced by reducing vanadium(V) oxide, V2O5, or vanadium(II) <span style="font-family: Arial,sans-serif; font-size: 11pt;">chloride, VCl2. <span style="font-family: Arial,sans-serif; font-size: 11pt;">Vanadium pentoxide V2O5 is an orange-yellow compound used as an oxidising agent and catalyst in the contact process for the manufacture of sulfuric acid. Many vanadium compounds form coloured solutions eg. the blue of the vanadyl ion, VO2+, has led to the use of vanadium compounds as glazes <span style="font-family: Arial,sans-serif; font-size: 11pt;">in the ceramics industry. A solution made by dissolving NH4VO3 in NaOH and then adding sulfuric acid is yellow due to the VO2+ ion. If this solution is shaken with zinc the colour gradually changes as the vanadium species is reduced: <span style="font-family: Arial,sans-serif; font-size: 11pt;"> VO2+(aq) → VO2+(aq) → V3+(aq) → V2+ (aq) <span style="font-family: Arial,sans-serif; font-size: 11pt;"> Yellow blue green violet

<span style="font-family: Arial,sans-serif; font-size: 11pt;">Iron, Fe <span style="font-family: Arial,sans-serif; font-size: 11pt;">Fe is the second most abundant metal in the earth's crust (after Al). It is mainly found in oxide ores e.g. magnetite Fe3O4 or in N.Z. in iron sand, titanomagnetite. It is also found in the bright, shiny yellow ore called "fool's gold", FeS. The strength of iron metal is improved by the addition of carbon to form steel, and also by alloying with other metals.

<span style="font-family: Arial,sans-serif; font-size: 11pt;">Fe is quite reactive and corrodes in moist air. It reacts with acids to form hydrogen gas and iron II (ferrous) or iron III (ferric) salts. Fe2+ is a mild reductant and Fe3+ is a mild oxidant. <span style="font-family: Arial,sans-serif; font-size: 11pt;"> //E//o(Fe3+/Fe2+ ) = + 0.77 V =<span style="font-family: Arial,sans-serif; font-size: 11pt;">Iron(II) sulfate, FeSO4, is a green soluble salt. Iron(II) sulfide, FeS, is black and insoluble. = <span style="font-family: Arial,sans-serif; font-size: 11pt;">If NaOH is added to a solution of Fe2+ a green gelatinous precipitate of Fe(OH)2 forms. This is readily oxidised by air to Fe2O3 - a red-brown iron(III) oxide (ferric oxide).

<span style="font-family: Arial,sans-serif; font-size: 11pt;">Iron(II) hydroxide (ferrous hydroxide) is a basic hydroxide i.e. it dissolves in acid not base. <span style="font-family: Arial,sans-serif; font-size: 11pt;"> Fe(OH)2 + 2H+ ® <span style="font-family: Arial,sans-serif; font-size: 11pt;"> Fe2+ + 2H2O <span style="font-family: Arial,sans-serif; font-size: 11pt;">Iron(III) oxide **-** Fe2O3 is also a basic oxide. <span style="font-family: Arial,sans-serif; font-size: 11pt;"> Fe2O3 + 6H+ ® <span style="font-family: Arial,sans-serif; font-size: 11pt;"> 2Fe3+ + 3H2O <span style="font-family: Arial,sans-serif; font-size: 11pt;">Aqueous solutions of iron(III) ions are yellow due to the presence of the [Fe(H2O)5OH]2+ ion. The proton tranfer to form this ion means a solution of Fe3+ is acidic, pKa(Fe3+,//aq//) = 2.17.

<span style="font-family: Arial,sans-serif; font-size: 11pt;">The presence of Fe3+ ions in solution is detected by the formation of the dark red complex ion FeSCN2+ when a solution of potassium thiocyanate is added. <span style="font-family: Arial,sans-serif; font-size: 11pt;"> Fe3+ + SCN - <span style="font-family: Arial,sans-serif; font-size: 11pt;"> [FeSCN]2+ <span style="font-family: Arial,sans-serif; font-size: 11pt;">Copper is an unreactive metal found mostly in sulfide ores. Cu is an excellent conductor of heat and electricity. Mixed with zinc it forms the alloy brass, and with tin it forms bronze. Cu is too unreactive <span style="font-family: Arial,sans-serif; font-size: 11pt;">a metal to displace hydrogen gas from dilute acids. <span style="font-family: Arial,sans-serif; font-size: 11pt;">Cu slowly corrodes in moist air (H2O, O2 and CO2) to form a pale green layer of basic copper carbonate, Cu2(OH)2CO3(s). This is what gives copper and bronze objects their characteristic green <span style="font-family: Arial,sans-serif; font-size: 11pt;">colour called patina. This compound adheres to the copper surface and protects the metal. <span style="font-family: Arial,sans-serif; font-size: 11pt;">Free cuprous ions (**Cu+**) are unstable in water and disproportionate to form metallic Cu and blue Cu2+ ions. Copper(I) oxide (Cu2O ) is the red precipitate that forms when the blue Cu2+ ions in Fehling’s solution or Benedicts solution are reduced by aldehydes.
 * <span style="font-family: Arial,sans-serif; font-size: 11pt;">Copper **

<span style="font-family: Arial,sans-serif; font-size: 11pt;">When KI(aq) is added to CuSO4(aq) a white precipitate of CuI is formed. <span style="font-family: Arial,sans-serif; font-size: 11pt;"> 2Cu2+(aq) + 4I - <span style="font-family: Arial,sans-serif; font-size: 11pt;">(aq) ® <span style="font-family: Arial,sans-serif; font-size: 11pt;"> 2CuI(s) + I2(aq) <span style="font-family: Arial,sans-serif; font-size: 11pt;">This is used in the volumetric analysis of copper in fungicides or alloys. <span style="font-family: Arial,sans-serif; font-size: 11pt;">Aqueous solutions of [Cu(H2O)6]2+ are blue. When dilute ammonia is added the insoluble light blue precipitate of Cu(OH)2 forms. As it is a basic hydroxide it dissolves in acid to give a solution of Cu2+. With excess ammonia, the precipitate dissolves as the royal blue complex ion [Cu(NH3)4]2+ forms.

<span style="font-family: Arial,sans-serif; font-size: 11pt;">Zinc <span style="font-family: Arial,sans-serif; font-size: 11pt;">Zinc is a silver reactive metal, used mainly for galvanising iron where it is protected by a hard film of basic carbonate. Typical of metal carbonates, this substance neutralises acid, eg. <span style="font-family: Arial,sans-serif; font-size: 11pt;"> ZnCO3 + 2HCl ® <span style="font-family: Arial,sans-serif; font-size: 11pt;"> ZnCl2 + H2O + CO2 <span style="font-family: Arial,sans-serif; font-size: 11pt;">The amphoteric nature of Zn, ZnO and Zn(OH)2 are covered on page 81. Zn(OH)2 dissolves in excess ammonia due to the formation of the colourless zinc tetrammine ion [Zn(NH3)4]2+. <span style="font-family: Arial,sans-serif; font-size: 11pt;">Formation of the Zn2+ ion occurs by the loss of the 4//s//2 electrons in the same way as the formation of the Ca2+ ion. However, the first ionisation energy of Zn is much higher because of the larger nuclear charge of the Zn compared to Ca.