Reactivity series explained

Reactivity series should not be confused with Electrochemical series.

In chemistry, a reactivity series (or reactivity series of elements) is an empirical, calculated, and structurally analytical progression of a series of metals, arranged by their "reactivity" from highest to lowest. 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.^[1]

Table

Metal	Ion	Reactivity	Extraction
Caesium Cs<	--Please don't add francium. Francium is very heavy, and so its electrons move fast enough that relativity must be considered. The end result is that the 7s electrons are stabilized, enough that Fr is probably actually LESS reactive than Cs! But nothing is known for sure.-->	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	Ba^2+
Strontium Sr	Sr^2+
Calcium Ca	Ca^2+
Magnesium Mg	Mg^2+	reacts very slowly with cold water, but rapidly in boiling water, and very vigorously with acids
Beryllium Be	Be^2+	reacts with acids and steam
Aluminium Al	Al^3+
Titanium Ti	Ti^4+	reacts with concentrated mineral acids	pyrometallurgical extraction using magnesium, or less commonly other alkali metals, hydrogen or calcium in the Kroll process
Manganese Mn	Mn^2+	reacts with acids; very poor reaction with steam	smelting with coke
Zinc Zn	Zn^2+
Chromium Cr	Cr^3+	aluminothermic reaction
Iron Fe	Fe^2+	smelting with coke
Cadmium Cd	Cd^2+
Cobalt Co	Co^2+
Nickel Ni	Ni^2+
Tin Sn	Sn^2+
Lead Pb	Pb^2+
Antimony Sb	Sb^3+	may react with some strong oxidizing acids	heat or physical extraction
Bismuth Bi	Bi^3+
Copper Cu	Cu^2+	reacts slowly with oxygen to form CuO
Tungsten W	W^3+	may react with some strong oxidizing acids
Mercury Hg	Hg^2+
Silver Ag	Ag^+
Gold Au	Au^3+^[2]
Platinum Pt	Pt^4+

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)
• This is not the electrochemical series, but Gold's oxidation potential is more than half a volt higher than Platinum's. It is thermodynamicaly favourable for Pt to form PtO in air, and then PtO2; but Au won't form oxides spontaneously. Pt is used in crucibles etc, but this is due to its better mp/mechanical properties!

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).

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".^[3]

The following list includes the metallic elements of the first six periods. It is mostly based on tables provided by NIST.^{[4] [5]} 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.)

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	Ba^2+ + 2 e^− → Ba	−2.91
38	Sr	strontium	Sr^2+ + 2 e^− → Sr	−2.90
20	Ca	calcium	Ca^2+ + 2 e^− → Ca	−2.87
11	Na	sodium	Na^+ + e^− → Na	−2.71
57	La	lanthanum	La^3+ + 3 e^− → La	−2.38
39	Y	yttrium	Y^3+ + 3 e^− → Y	−2.38
12	Mg	magnesium	Mg^2+ + 2 e^− → Mg	−2.36
59	Pr	praseodymium	Pr^3+ + 3 e^− → Pr	−2.35
58	Ce	cerium	Ce^3+ + 3 e^− → Ce	−2.34
68	Er	erbium	Er^3+ + 3 e^− → Er	−2.33
67	Ho	holmium	Ho^3+ + 3 e^− → Ho	−2.33
60	Nd	neodymium	Nd^3+ + 3 e^− → Nd	−2.32
69	Tm	thulium	Tm^3+ + 3 e^− → Tm	−2.32
62	Sm	samarium	Sm^3+ + 3 e^− → Sm	−2.30
61	Pm	promethium	Pm^3+ + 3 e^− → Pm	−2.30
66	Dy	dysprosium	Dy^3+ + 3 e^− → Dy	−2.29
71	Lu	lutetium	Lu^3+ + 3 e^− → Lu	−2.28
65	Tb	terbium	Tb^3+ + 3 e^− → Tb	−2.28
64	Gd	gadolinium	Gd^3+ + 3 e^− → Gd	−2.28
70	Yb	ytterbium	Yb^3+ + 3 e^− → Yb	−2.19
21	Sc	scandium	Sc^3+ + 3 e^− → Sc	−2.09
63	Eu	europium	Eu^3+ + 3 e^− → Eu	−1.99
4	Be	beryllium	Be^2+ + 2 e^− → Be	−1.97
13	Al	aluminium	Al^3+ + 3 e^− → Al	−1.68
22	Ti	titanium	Ti^3+ + 3 e^− → Ti	−1.37
25	Mn	manganese	Mn^2+ + 2 e^− → Mn	−1.18
23	V	vanadium	V^2+ + 2 e^− → V	−1.12
24	Cr	chromium	Cr^2+ + 2 e^− → Cr	−0.89
30	Zn	zinc	Zn^2+ + 2 e^− → Zn	−0.76
31	Ga	gallium	Ga^3+ + 3 e^− → Ga	−0.55
26	Fe	iron	Fe^2+ + 2 e^− → Fe	−0.44
48	Cd	cadmium	Cd^2+ + 2 e^− → Cd	−0.40
49	In	indium	In^3+ + 3 e^− → In	−0.34
81	Tl	thallium	Tl^+ + e^− → Tl	−0.34
27	Co	cobalt	Co^2+ + 2 e^− → Co	−0.28
28	Ni	nickel	Ni^2+ + 2 e^− → Ni	−0.24
50	Sn	tin	Sn^2+ + 2 e^− → Sn	−0.14
82	Pb	lead	Pb^2+ + 2 e^− → Pb	−0.13
1	H	hydrogen	2 H^+ + 2 e^− → H2	0.00
32	Ge	germanium	Ge^2+ + 2 e^− → Ge	+0.1
51	Sb	antimony	Sb^3+ + 3 e^− → Sb	+0.15
83	Bi	bismuth	Bi^3+ + 3 e^− → Bi	+0.31
29	Cu	copper	Cu^2+ + 2 e^− → Cu	+0.34
84	Po	polonium	Po^2+ + 2 e^− → Po	+0.6
44	Ru	ruthenium	Ru^3+ + 3 e^− → Ru	+0.60
45	Rh	rhodium	Rh^3+ + 3 e^− → Rh	+0.76
47	Ag	silver	Ag^+ + e^− → Ag	+0.80
80	Hg	mercury	Hg^2+ + 2 e^− → Hg	+0.85
46	Pd	palladium	Pd^2+ + 2 e^− → Pd	+0.92
77	Ir	iridium	Ir^3+ + 3 e^− → Ir	+1.0
85	At	astatine	At^+ + e^− → At	+1.0
78	Pt	platinum	Pt^2+ + 2 e^− → Pt	+1.18
79	Au	gold	Au^3+ + 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.

Comparison with electronegativity values

The image shows a periodic table extract with the electronegativity values of metals.^[6]

Wulfsberg^[7] 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.

See also

• Reactivity (chemistry), which discusses the inconsistent way that the term 'reactivity' is used in chemistry.

External links

• Science Line Chemistry

Notes and References

1. Web site: Metal extraction and the reactivity series - The reactivity series of metals - GCSE Chemistry (Single Science) Revision - WJEC . 2023-03-24 . BBC Bitesize . en-GB.
2. Book: Wulsberg, Gary. 2000. Inorganic Chemistry. 294. 9781891389016.
3. by A. V. Kulsha and T. A. Kolevich gives:
4. https://www.nist.gov/system/files/documents/2019/04/02/jpcrd355.pdf Standard Electrode Potentials and Temperature Coefficients in Water at 298.15 K
5. For antimony: Antimony - Physico-chemical properties - DACTARI
6. Book: Aylward . G . Findlay . T . 2008 . SI Chemical Data . 6. Milton, Queensland. John Wiley & Sons. 126. 978-0-470-81638-7.
7. Book: Wulfsberg. G . 2018 . Foundations of Inorganic Chemistry. Mill Valley. University Science Books . 319 . 978-1-891389-95-5.