Reactivity Series Definition in Chemistry

The reactivity series is a list of metals ranked in order of decreasing reactivity, which is usually determined by the ability to displace hydrogen gas from water and acid solutions. It can be used to predict which metals will displace other metals in aqueous solutions in double displacement reactions and to extract metals from mixtures and ores. The reactivity series is also known as the activity series.

List of Metals

The reactivity series follows the order, from most reactive to least reactive:

• Cesium
• Francium
• Rubidium
• Potassium
• Sodium
• Lithium
• Barium
• Radium
• Strontium
• Calcium
• Magnesium
• Beryllium
• Aluminum
• Titanium(IV)
• Manganese
• Zinc
• Chromium(III)
• Iron(II)
• Cadmium
• Cobalt(II)
• Nickel
• Tin
• Lead
• Antimony
• Bismuth(III)
• Copper(II)
• Tungsten
• Mercury
• Silver
• Gold
• Platinum

Thus, cesium is the most reactive metal on the periodic table. In general, the alkali metals are the most reactive, followed by the alkaline earths and transition metals. The noble metals (silver, platinum, gold) are not very reactive. The alkali metals, barium, radium, strontium, and calcium are sufficiently reactive that they react with cold water. Magnesium reacts slowly with cold water, but quickly with boiling water or acids. Beryllium and aluminum react with steam and acids. Titanium only reacts with the concentrated mineral acids. The majority of transition metals react with acids, but generally not with steam. The noble metals only react with strong oxidizers, such as aqua regia.

Reactivity Series Trends

In summary, moving from the top to the bottom of the reactivity series, the following trends become apparent:

• Reactivity decreases. The most reactive metals are on the bottom left side of the periodic table.
• Atoms lose electrons less easily to form cations.
• Metals become less likely to oxidize, tarnish, or corrode.
• Less energy is needed to isolate the metallic elements from their compounds.
• The metals become weaker electron donors or reducing agents.

Reactions Used to Test Reactivity

The three types of reactions used to test reactivity are reaction with cold water, reaction with acid, and single displacement reactions. The most reactive metals react with cold water to yield the metal hydroxide and hydrogen gas. Reactive metals react with acids to yield the metal salt and hydrogen. Metals that do not react in water may react in acid. When metal reactivity is to be directly compared, a single displacement reaction serves the purpose. A metal will displace any metal lower in the series. For example, when an iron nail is placed in a copper sulfate solution, iron is converted to iron(II) sulfate, while copper metal forms on the nail. The iron reduces and displaces the copper.

Reactivity Series vs. Standard Electrode Potentials

The reactivity of metals may also be predicted by reversing the order of standard electrode potentials. This ordering is called the electrochemical series. The electrochemical series is also the same as the reverse order of the ionization energies of elements in their gas phase. The order is:

• Lithium
• Cesium
• Rubidium
• Potassium
• Barium
• Strontium
• Sodium
• Calcium
• Magnesium
• Beryllium
• Aluminum
• Hydrogen (in water)
• Manganese
• Zinc
• Chromium(III)
• Iron(II)
• Cadmium
• Cobalt
• Nickel
• Tin
• Lead
• Hydrogen (in acid)
• Copper
• Iron(III)
• Mercury
• Silver
• Palladium
• Iridium
• Platinum(II)
• Gold

The most significant difference between the electrochemical series and the reactivity series is that the positions of sodium and lithium are switched. The advantage of using standard electrode potentials to predict reactivity is that they are a quantitative measure of reactivity. In contrast, the reactivity series is a qualitative measure of reactivity. The major disadvantage of using standard electrode potentials is that they only apply to aqueous solutions under standard conditions. Under real-world conditions, the series follows the trend potassium > sodium > lithium > alkaline earths.

Sources

• Bickelhaupt, F. M. (1999-01-15). "Understanding reactivity with Kohn–Sham molecular orbital theory: E2–SN2 mechanistic spectrum and other concepts". Journal of Computational Chemistry. 20 (1): 114–128. doi:10.1002/(sici)1096-987x(19990115)20:1<114::aid-jcc12>3.0.co;2-l
• Briggs, J. G. R. (2005). Science in Focus, Chemistry for GCE 'O' Level. Pearson Education.
• Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. pp. 82–87. ISBN 978-0-08-022057-4.
• Lim Eng Wah (2005). Longman Pocket Study Guide 'O' Level Science-Chemistry. Pearson Education.
• Wolters, L. P.; Bickelhaupt, F. M. (2015). "The activation strain model and molecular orbital theory". Wiley Interdisciplinary Reviews: Computational Molecular Science. 5 (4): 324–343. doi:10.1002/wcms.1221