<text><span class="style10">etals (4 of 4)</span><span class="style7"></span><span class="style10">THE REACTIVITY SERIES</span><span class="style7">The widely varying reactivity of metals can be related to their positions in the Periodic Table. The s-block metals are highly reactive, while the transition metals typically become less reactive from left to right across the table, with the noble and coinage metals least re active of all.When metals react, they usually lose electrons to form positively charged ions (cations, see p. 44). This charge (also known as the oxidation state) is again related to the position of a metal in the Periodic Table. In the s-block, the charge equals the group number, +1 or +2 (e.g. K+, Mg2+). In the transition metals, variability of oxidation state is the rule: for instance, iron may lose 2 or 3 electrons (Fe2+, Fe3+), and this fact is indicated in the names and formulae of its compounds - iron(II) chloride (FeCl2) and iron(III) chloride (FeCl3).The reactivity of a metal can thus be explained in terms of its readiness to lose electrons to form cations: potassium (K) readily loses an electron to form a K+ ion, while gold (Au) is highly unreactive and dissolves only in aqua regia, a fiercely oxidizing mixture of hydrochloric and nitric acids. Metals can be placed in order of reactivity, in a sequence known as the reactivity series ; for some of the more important metals, the series runs as follows (in order of decreasing reactivity): K Na Ca Mg Al Zn Fe Pb Cu Hg Ag Au PtA metal can be displaced from a solution of one of its salts simply by addition of a metal higher (earlier) in the series. For in stance, if zinc metal (Zn) is added to a solution of copper(II) sulfate (CuSO4), the zinc becomes coated by copper metal and the blue color of the solution fades, as the colored copper ions in solution are displaced by zinc ions: Zn(s) + Cu2+(aq) + SO42-(aq) Zn2+(aq) + SO42-(aq) + Cu(s)The reactivity series also indicates the affinity of a metal for oxygen. As such, it explains the differing susceptibility of metals to corrosion (surface oxidation) and underlies the extraction of metals from their oxides. The more reactive a metal is, the higher the temperature required to reduce its oxide by carbon. In practice, the most reactive metals cannot be economically reduced by carbon, and are therefore obtained by electrolysis or by displacement by an even more reactive metal.The reactivity series can also be seen as an electrochemical series. When two different metals are dipped into an electrolyte solution, a voltage forms between them and the metal higher in the series becomes the anode (positive electrode). The distance between the two metals in the series reflects the size of the voltage produced. Electrochemical reactions of this kind underlie electroplating and the operation of electrolytic cells and batteries. Frequently some hydrogen is also produced: such a reaction often occurs in domestic central heating systems, where copper pipes and iron radiators are both in contact with hot water; the `air' that accumulates in the system is actually hydrogen.</span></text>
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<text><span class="style10">etal and the Periodic Table.</span><span class="style7"></span></text>
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<id>23</id>
<text>ΓÇó ELECTROMAGNETISMΓÇó ELECTRICITY IN ACTIONΓÇó ATOMS AND SUBATOMIC PARTICLESΓÇó ELEMENTS AND THE PERIODIC TABLEΓÇó CHEMICAL BONDSΓÇó CHEMICAL REACTIONSΓÇó MINING, MINERALS AND METALSΓÇó IRON AND STEELΓÇó HUMAN PREHISTORY</text>
