Reactivity series
In chemistry, a reactivity series (or activity series) is an empirical, calculated, and structurally analytical progression[1] of a series of metals, arranged by their "reactivity" from highest to lowest.[2][3][4] It is used to summarize information about the reactions of metals with acids and water, single displacement reactions and the extraction of metals from their ores.
Table
| Metal | Ion | Reactivity | Extraction |
|---|---|---|---|
| Caesium Cs | Cs+ | reacts with cold water | electrolysis |
| Rubidium Rb | Rb+ | ||
| Potassium K | K+ | ||
| Sodium Na | Na+ | ||
| Lithium Li | Li+ | ||
| radon Ra | Ra2+ | ||
| Barium Ba | Ba2+ | ||
| Strontium Sr | Sr2+ | ||
| Calcium Ca | Ca2+ | ||
| Magnesium Mg | Mg2+ | ||
| Beryllium Be | Be2+ | reacts with acids and steam | |
| Aluminium Al | Al3+ | ||
| Titanium Ti | Ti4+ | reacts with concentrated mineral acids | pyrometallurgical extraction using magnesium, or less commonly other alkali metals, hydrogen or calcium in the Kroll process |
| Manganese Mn | Mn2+ | reacts with acids; very poor reaction with steam | smelting with coke |
| Zinc Zn | Zn2+ | ||
| Chromium Cr | Cr3+ | aluminothermic reaction | |
| Iron Fe | Fe2+ | smelting with coke | |
| Cadmium Cd | Cd2+ | ||
| Cobalt Co | Co2+ | ||
| Nickel Ni | Ni2+ | ||
| Tin Sn | Sn2+ | ||
| Lead Pb | Pb2+ | ||
| Antimony Sb | Sb3+ | may react with some strong oxidizing acids | heat or physical extraction |
| Bismuth Bi | Bi3+ | ||
| Copper Cu | Cu2+ | reacts slowly with air | |
| Tungsten W | W3+ | may react with some strong oxidizing acids | |
| Mercury Hg | Hg2+ | ||
| Silver Ag | Ag+ | ||
| Gold Au | Au3+[5][6] | ||
| Platinum Pt | Pt4+ |
Going from the bottom to the top of the table the metals:
- increase in reactivity;
- lose electrons (oxidize) more readily to form positive ions;
- corrode or tarnish more readily;
- require more energy (and different methods) to be isolated from their compounds;
- become stronger reducing agents (electron donors).
Defining reactions
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).[5]
Reaction with water and acids
The most reactive metals, such as sodium, will react with cold water to produce hydrogen and the metal hydroxide:
- 2 Na (s) + 2 H2O (l) →2 NaOH (aq) + H2 (g)
Metals in the middle of the reactivity series, such as iron, will react with acids such as sulfuric acid (but not water at normal temperatures) to give hydrogen and a metal salt, such as iron(II) sulfate:
- Fe (s) + H2SO4 (l) → FeSO4 (aq) + H2 (g)
There is some ambiguity at the borderlines between the groups. Magnesium, aluminium and zinc can react with water, but the reaction is usually very slow unless the metal samples are specially prepared to remove the surface layer of oxide which protects the rest of the metal. Copper and silver will react with nitric acid; but because nitric acid is an oxidizing acid, the oxidizing agent is not the H+ ion as in normal acids, but the NO3− ion.
Comparison with standard electrode potentials
The reactivity series is sometimes quoted in the strict reverse order of standard electrode potentials, when it is also known as the "electrochemical series" :-
- Li > Cs > Rb > K > Ba > Sr > Ca > Na > La > Y > Mg > Ce > Sc > Be > Al > Ti > Mn > V > Cr > Zn > Ga > Fe > Cd > In > Tl > Co > Ni > Sn > Pb > (H) > Sb > Bi > Cu > Po > Ru > Rh > Ag > Hg > Pd > Ir > Pt > Au[7]
The positions of lithium and sodium are changed on such a series. Apart from the other lanthanides (Pr-Lu), the series quoted above includes all metallic elements from the first six periods except for the few that do not form mostly unhydrolysed aqua cations (Zr-Tc, Hf-Os).
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 for standard conditions: 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
- potassium > sodium > lithium > alkaline earth metals,
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 a eutectic mixture of lithium chloride and potassium chloride: lithium metal is formed at the cathode, not potassium.[1]
See also
- Reactivity (chemistry), which discusses the inconsistent way that the term 'reactivity' is used in chemistry.
References
- ^ a b Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. pp. 82–87. ISBN 978-0-08-022057-4.
- ^ France, Colin (2008), The Reactivity Series of Metals
- ^ Briggs, J. G. R. (2005), Science in Focus, Chemistry for GCE 'O' Level, Pearson Education, p. 172
- ^ Lim Eng Wah (2005), Longman Pocket Study Guide 'O' Level Science-Chemistry, Pearson Education, p. 190
- ^ a b http://www.cod.edu/people/faculty/jarman/richenda/1551_hons_materials/Activity%20series.htm
- ^ Wulsberg, Gary (2000). Inorganic Chemistry. p. 294. ISBN 9781891389016.
- ^ Periodic table poster by A. V. Kulsha and T. A. Kolevich
