require more energy (and different methods) to be separated from their ores;
become stronger reducing agents (electron donors).
There is no unique and fully consistent way to define the reactivity series, but it is common to use the three types of reaction listed below, many of which can be performed in a high-school laboratory (at least as demonstrations).
Metals in the middle of the reactivity series, such asiron, will react with acids such assulfuric acid(but not water at normal temperatures) to give hydrogen and a metalsalt, such asiron(II) sulfate:
An iron nail placed in a solution ofcopper sulfatewill quickly change colour as metallic copper is deposited and the iron is converted intoiron(II) sulfate:
Fe (s) + CuSO4(aq) → Cu (s) + FeSO4(aq)
Similarly,magnesiumcan be used to extracttitaniumfromtitanium tetrachloride, formingmagnesium chloridein the process:
2 Mg (s) + TiCl4(l) → Ti (s) + 2 MgCl2(s)
However, other factors can come into play, such as in the preparation of metallicpotassiumby the reduction ofpotassium chloridewith sodium at 850 °C. Although sodium is lower than potassium in the reactivity series, the reaction can proceed because potassium is more volatile, and is distilled off from the mixture.
Na (g) + KCl (l) → K (g) + NaCl (l)
Comparison with standard electrode potentials
The reactivity series is sometimes quoted in the strict reverse order ofstandard electrode potentials, when it is also known as the "electrochemical series":
Li > K > Sr > Na > Ca > Mg > Al > Mn > Zn > Cr(+3) > Fe > Cd > Co > Ni > Sn > Pb > H > Cu > Hg > Ag > Pd > Ir > Pt > Au
The positions oflithiumandsodiumare changed on such a series; gold and platinum are in joint position and not gold leading, although this has little practical significance as both metals are highly unreactive.
Standard electrode potentials offer a quantitative measure of the power of a reducing agent, rather than the qualitative considerations of other reactive series. However, they are only valid forstandardconditions: in particular, they only apply to reactions in aqueous solution. Even with this proviso, the electrode potentials of lithium and sodium – and hence their positions in the electrochemical series – appear anomalous. The order of reactivity, as shown by the vigour of the reaction with water or the speed at which the metal surface tarnishes in air, appears to be
the same as the reverse order of the (gas-phase)ionization energies. This is borne out by the extraction of metallic lithium by the electrolysis of aeutecticmixture oflithium chlorideandpotassium chloride: lithium metal is formed at the cathode, not potassium.
In a reactivity series, the most reactive element is placed at the top and the least reactive element at the bottom. More reactive metals have a greater tendency to lose electrons and form positive ions.
Areactivity series of metals could include any elements. For example:
A good way to remember the order of a reactivity series of metals is to use the first letter of each one to make up a silly sentence. For example: People Say Little Children Make AZebra Ill ConstantlySniffing Giraffes.
Observations of the way that these elements react with water, acidsand steam enable us to put them into this series.
The tables show how the elements react with water and dilute acids:
Note that aluminium can be difficult to place in the correct position in the reactivity series during these experiments. This is because its protective aluminium oxide layer makes it appear to be less reactive than it really is. When this layer is removed, the observations are more reliable.