Reactivity series

In chemistry, a reactivity series (or reactivity series of elements) 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.^[5]

Table

Metal	Ion	Reactivity	Extraction
Caesium Cs	Cs⁺	reacts with cold water	Electrolysis (a.k.a. electrolytic refining)
Rubidium Rb	Rb⁺
Potassium K	K⁺
Sodium Na	Na⁺
Lithium Li	Li⁺
Barium Ba	Ba²⁺
Strontium Sr	Sr²⁺
Calcium Ca	Ca²⁺
Magnesium Mg	Mg²⁺	reacts very slowly with cold water, but rapidly in boiling water, and very vigorously with acids
Beryllium Be	Be²⁺	reacts with acids and steam
Aluminium Al	Al³⁺	reacts with acids and steam
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⁺		smelting with coke
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⁺	may react with some strong oxidizing acids
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⁺^[6]^[7]
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).^[6]

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 passivation 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".^[8]

The following list includes the metallic elements of the first six periods. It is mostly based on tables provided by NIST.^[9]^[10] However, not all sources give the same values: there are some differences between the precise values given by NIST and the CRC Handbook of Chemistry and Physics. In the first six periods this does not make a difference to the relative order, but in the seventh period it does, so the seventh-period elements have been excluded. (In any case, the typical oxidation states for the most accessible seventh-period elements thorium and uranium are too high to allow a direct comparison.)^[11]

Hydrogen has been included as a benchmark, although it is not a metal. Borderline germanium, antimony, and astatine have been included. Some other elements in the middle of the 4d and 5d rows have been omitted (Zr–Tc, Hf–Os) when their simple cations are too highly charged or of rather doubtful existence. Greyed-out rows indicate values based on estimation rather than experiment.

Z	Sym	Element	Reaction	E° (V)
3	Li	lithium	Li⁺ + e⁻ → Li	−3.04
55	Cs	caesium	Cs⁺ + e⁻ → Cs	−3.03
37	Rb	rubidium	Rb⁺ + e⁻ → Rb	−2.94
19	K	potassium	K⁺ + e⁻ → K	−2.94
56	Ba	barium	Ba²⁺ + 2 e⁻ → Ba	−2.91
38	Sr	strontium	Sr²⁺ + 2 e⁻ → Sr	−2.90
20	Ca	calcium	Ca²⁺ + 2 e⁻ → Ca	−2.87
11	Na	sodium	Na⁺ + e⁻ → Na	−2.71
57	La	lanthanum	La³⁺ + 3 e⁻ → La	−2.38
39	Y	yttrium	Y³⁺ + 3 e⁻ → Y	−2.38
12	Mg	magnesium	Mg²⁺ + 2 e⁻ → Mg	−2.36
59	Pr	praseodymium	Pr³⁺ + 3 e⁻ → Pr	−2.35
58	Ce	cerium	Ce³⁺ + 3 e⁻ → Ce	−2.34
68	Er	erbium	Er³⁺ + 3 e⁻ → Er	−2.33
67	Ho	holmium	Ho³⁺ + 3 e⁻ → Ho	−2.33
60	Nd	neodymium	Nd³⁺ + 3 e⁻ → Nd	−2.32
69	Tm	thulium	Tm³⁺ + 3 e⁻ → Tm	−2.32
62	Sm	samarium	Sm³⁺ + 3 e⁻ → Sm	−2.30
61	Pm	promethium	Pm³⁺ + 3 e⁻ → Pm	−2.30
66	Dy	dysprosium	Dy³⁺ + 3 e⁻ → Dy	−2.29
71	Lu	lutetium	Lu³⁺ + 3 e⁻ → Lu	−2.28
65	Tb	terbium	Tb³⁺ + 3 e⁻ → Tb	−2.28
64	Gd	gadolinium	Gd³⁺ + 3 e⁻ → Gd	−2.28
70	Yb	ytterbium	Yb³⁺ + 3 e⁻ → Yb	−2.19
21	Sc	scandium	Sc³⁺ + 3 e⁻ → Sc	−2.09
63	Eu	europium	Eu³⁺ + 3 e⁻ → Eu	−1.99
4	Be	beryllium	Be²⁺ + 2 e⁻ → Be	−1.97
13	Al	aluminium	Al³⁺ + 3 e⁻ → Al	−1.68
22	Ti	titanium	Ti³⁺ + 3 e⁻ → Ti	−1.37
25	Mn	manganese	Mn²⁺ + 2 e⁻ → Mn	−1.18
23	V	vanadium	V²⁺ + 2 e⁻ → V	−1.12
24	Cr	chromium	Cr²⁺ + 2 e⁻ → Cr	−0.89
30	Zn	zinc	Zn²⁺ + 2 e⁻ → Zn	−0.76
31	Ga	gallium	Ga³⁺ + 3 e⁻ → Ga	−0.55
26	Fe	iron	Fe²⁺ + 2 e⁻ → Fe	−0.44
48	Cd	cadmium	Cd²⁺ + 2 e⁻ → Cd	−0.40
49	In	indium	In³⁺ + 3 e⁻ → In	−0.34
81	Tl	thallium	Tl⁺ + e⁻ → Tl	−0.34
27	Co	cobalt	Co²⁺ + 2 e⁻ → Co	−0.28
28	Ni	nickel	Ni²⁺ + 2 e⁻ → Ni	−0.24
50	Sn	tin	Sn²⁺ + 2 e⁻ → Sn	−0.14
82	Pb	lead	Pb²⁺ + 2 e⁻ → Pb	−0.13
1	H	hydrogen	2 H⁺ + 2 e⁻ → H₂	0.00
32	Ge	germanium	Ge²⁺ + 2 e⁻ → Ge	+0.1
51	Sb	antimony	Sb³⁺ + 3 e⁻ → Sb	+0.15
83	Bi	bismuth	Bi³⁺ + 3 e⁻ → Bi	+0.31
29	Cu	copper	Cu²⁺ + 2 e⁻ → Cu	+0.34
84	Po	polonium	Po²⁺ + 2 e⁻ → Po	+0.6
44	Ru	ruthenium	Ru³⁺ + 3 e⁻ → Ru	+0.60
45	Rh	rhodium	Rh³⁺ + 3 e⁻ → Rh	+0.76
47	Ag	silver	Ag⁺ + e⁻ → Ag	+0.80
80	Hg	mercury	Hg²⁺ + 2 e⁻ → Hg	+0.85
46	Pd	palladium	Pd²⁺ + 2 e⁻ → Pd	+0.92
77	Ir	iridium	Ir³⁺ + 3 e⁻ → Ir	+1.0
85	At	astatine	At⁺ + e⁻ → At	+1.0
78	Pt	platinum	Pt²⁺ + 2 e⁻ → Pt	+1.18
79	Au	gold	Au³⁺ + 3 e⁻ → Au	+1.50

The positions of lithium, sodium and gold are changed on such a series.

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, sodium and gold – 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

Cs > K > Na > Li > alkaline earth metals,

i.e., alkali metals > 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]

Comparison with electronegativity values

The image shows a periodic table extract with the electronegativity values of metals.^[12]

Wulfsberg^[13] distinguishes:
   very electropositive metals with electronegativity values below 1.4
   electropositive metals with values between 1.4 and 1.9; and
   electronegative metals with values between 1.9 and 2.54.

From the image, the group 1–2 metals and the lanthanides and actinides are very electropositive to electropositive; the transition metals in groups 3 to 12 are very electropositive to electronegative; and the post-transition metals are electropositive to electronegative. The noble metals, inside the dashed border (as a subset of the transition metals) are very electronegative.

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
^ "Metal extraction and the reactivity series - The reactivity series of metals - GCSE Chemistry (Single Science) Revision - WJEC". BBC Bitesize. Retrieved 2023-03-24.
^ ^a ^b Activity series at the Wayback Machine (archived 2019-05-07)
^ Wulsberg, Gary (2000). Inorganic Chemistry. p. 294. ISBN 9781891389016.
^ Periodic table poster at the Wayback Machine (archived 2022-02-24) by A. V. Kulsha and T. A. Kolevich gives:
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
^ Standard Electrode Potentials and Temperature Coefficients in Water at 298.15 K, Steven G. Bratsch (NIST)
^ For antimony: Antimony - Physico-chemical properties - DACTARI
^ Lide, David R., ed. (2006). CRC Handbook of Chemistry and Physics (87th ed.). Boca Raton, FL: CRC Press. ISBN 0-8493-0487-3.
^ Aylward, G; Findlay, T (2008). SI Chemical Data (6 ed.). Milton, Queensland: John Wiley & Sons. p. 126. ISBN 978-0-470-81638-7.
^ Wulfsberg, G (2018). Foundations of Inorganic Chemistry. Mill Valley: University Science Books. p. 319. ISBN 978-1-891389-95-5.

External links

Science Line Chemistry

[G&E-1] Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. pp. 82–87. ISBN 978-0-08-022057-4.

[2] France, Colin (2008), The Reactivity Series of Metals

[3] Briggs, J. G. R. (2005), Science in Focus, Chemistry for GCE 'O' Level, Pearson Education, p. 172

[4] Lim Eng Wah (2005), Longman Pocket Study Guide 'O' Level Science-Chemistry, Pearson Education, p. 190

[5] "Metal extraction and the reactivity series - The reactivity series of metals - GCSE Chemistry (Single Science) Revision - WJEC". BBC Bitesize. Retrieved 2023-03-24.

[:0-6] Activity series at the Wayback Machine (archived 2019-05-07)

[7] Wulsberg, Gary (2000). Inorganic Chemistry. p. 294. ISBN 9781891389016.

[8] Periodic table poster at the Wayback Machine (archived 2022-02-24) by A. V. Kulsha and T. A. Kolevich gives:
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

[9] Standard Electrode Potentials and Temperature Coefficients in Water at 298.15 K, Steven G. Bratsch (NIST)

[10] For antimony: Antimony - Physico-chemical properties - DACTARI

[CRC-11] Lide, David R., ed. (2006). CRC Handbook of Chemistry and Physics (87th ed.). Boca Raton, FL: CRC Press. ISBN 0-8493-0487-3.

[12] Aylward, G; Findlay, T (2008). SI Chemical Data (6 ed.). Milton, Queensland: John Wiley & Sons. p. 126. ISBN 978-0-470-81638-7.

[13] Wulfsberg, G (2018). Foundations of Inorganic Chemistry. Mill Valley: University Science Books. p. 319. ISBN 978-1-891389-95-5.

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