Metals, in general, are substances which have high electrical conductivity, high thermal conductivity, and high density. Typically they are malleable and ductile, deforming under stress without cleaving. In terms of optical properties, metals are shiny and lustrous. This article is on reactivity series of metals.
Metals are usually inclined to form cations through electron loss, reacting with oxygen in the air to form oxides over various timescales (iron rusts over years, while potassium burns in seconds). Examples:
- 4 Na + O2 → 2 Na2O (sodium oxide)
- 2 Ca + O2 → 2 CaO (calcium oxide)
- 4 Al + 3 O2 → 2 Al2O3 (aluminium oxide).
The transition metals (such as iron, copper, zinc, and nickel) are slower to oxidize because they form a passive layer of oxide that protects the interior. Others, like palladium, platinum and gold do not react with the atmosphere at all.
Reactivity Series of Metals
Reactivity Series in chemistry is an experimental, structural and logical progression of series of metals in order of reactivity from highest to lowest. Metals react differently with different substances. It gives a descriptive detail on metal reactions with the extraction of metals from ores and with acids and water. In other words, the most reactive metal is presented at the top and the least reactive metal at the bottom, as shown in the reactivity series chart below.
All metals have a tendency to lose electrons and form metal ions. In other words, all metals are good reducing agents and easily oxidize themselves.
The reactivity series of metals can be shown in another way, which includes oxidation reaction of each metal to the respective metal ion. It gives information regarding the reducing power of the metal atom and the oxidation number of the metal ion.
Before discussing the reactivity order of metals, it is important to discuss about the differences between metals and non-metals.
Differences between metals & non-metals:
|1||Malleable & ductile in nature||Brittle in nature|
|2||Good conductor of heat & electricity||Insulator in nature|
|3||Form ionic compounds||Form covalent compounds|
|4||Have lustrous surface||Not applicable|
|5||Have high melting point||Low melting point compared to metals|
|6||Usually solid at room temperature||Can exist in solid, liquid & gaseous state|
|7||They are good reducing agents||Good oxidizing agent|
|8||Form basic oxides||Form acidic oxides|
|9||Have low electronegativity||High electronegativity|
|10||Have a tendency to lose electrons||Have a tendency to gain electrons|
Reactivity Series of metals Chart
In the reactivity series, as we move from bottom to top, the reactivity of metals increases. Metals present at the top of the series can lose electrons more readily to form positive ions and corrode or tarnish more readily. They require more energy to be separated from their ores, and become stronger reducing agents, while metals present at the bottom of the series are good oxidizing agent.
We can summarize the reactivity of metals in a reactivity series chart as shown below:
|Lithium||Li||Displaces H2 gas from water, steam and acids and forms hydroxides.||Electrolysis|
|Magnesium||Mg||Displaces H2 gas from steam and acids and forms hydroxides.|
|Carbon||C||Included for comparison.|
|Manganese||Mn||Displaces H2 gas from steam and acids and forms hydroxides.||Smelting with coke|
|Iron||Fe||Displaces H2 gas from acids only and forms hydroxides.|
|Hydrogen gas||H2||Included for comparison.|
|Antimony||Sb||Combines with O2 to form oxides and cannot displace H2.||Heat or physical extraction methods.|
|Mercury||Hg||Found free in nature, oxides decompose with heating.|
- Silver, gold, and platinum are metals with the least reactivity. They are found in nature.
- The metals with high reactive series in the above table also indicates that reverse reaction is a bit tough process.
- Reactions are mostly Exothermic in case of highly reactive metals.
- The reaction takes place fast in highly reactive metals.
- Metals which are present above the carbon are extracted using electrolysis method.
- Carbon and hydrogen plays and plays vital role in terms of a method that involves metal extraction.
Reaction with Water and Acids:
Sodium is a most reactive metal. It produces hydrogen and metal hydroxide when it reacts with cold water.
2Na(S) + 2H2O(l) → 2NaOH(aq) + H2(g)
Iron which is present in the middle of the table of the reactive series when reacted with sulfuric acid produces hydrogen and metal salt namely iron sulphate.
Fe(s) + H2So4(l) → FeSo4(aq) + H2(g)
Significance and usage of reactivity series of metals:
- By using the reactivity series of metals, one can predict the products of displacement reaction. Each element in the reactivity series can be replaced from a compound by any of the elements above it. For example, magnesium metal can displace zinc ions in a solution. Mg(s) + Zn2+ →→ Zn(s) + Mg2+
- The interval between metals in the reactivity series of metals represents the reactivity of those metals towards each other. If the interval between elements is larger, they will react more vigorously. The topmost five elements, form lithium to sodium are known as very active metals; hence they react with cold water to produce the hydroxide and hydrogen gas. For example, sodium forms sodium hydroxide and hydrogen gas with cold water. 2Na + 2H2O →→ 2NaOH + H2
- From magnesium to chromium, elements are considered as active metals and they will react with very hot water or steam and form the oxide and hydrogen gas. For example, aluminum reacts with steam to form aluminum oxide and hydrogen gas.
2Al + 3H2O →→ Al2O3 + 3H2
- From iron to lead, metals can replace hydrogen from various acids like hydrochloric acid, dilute sulfuric and nitric acids. Oxides of these metals undergo reduction when heated with hydrogen gas, carbon, or carbon monoxide. Till copper, metals can combine directly with oxygen and form a metal oxide. Elements present at the bottom from mercury to gold are often found in the native form in nature and their oxides show thermal decomposition under mild conditions.
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