On the basis of physical and chemical properties, all elements can be classified as metals and non-metals. Metals are electropositive elements and placed at the left side of the periodic table. We know that the long form of the periodic table is based on the atomic number of elements. All elements are placed in the increasing order of their atomic number. The long form of the periodic table has 18 vertical columns which are known as groups whereas horizontal rows in the table are called as periods. Non-metals are placed at the right side of the periodic table.
Elements with intermediate properties are known as metalloids. Metals are more reactive due to the presence of 1, 2, or 3 electrons in their valence shell. They have a tendency to lose electrons for getting the Nobel gas configuration. That is the reason; metals are usually converted into metal cations by losing electrons. Different metals can react with other reagents with different reactivity.
How can you determine the reactivity of metals with respect to different reagents? There must be some criteria that help in the determination of reactivity of elements. Activity series or reactivity series can be used to compare the reactivity of different metals. The series of elements in which they are arranged in the increasing order of their reactivity is called as activity series.
A replacement reaction takes place when one metal replaces the other in
its aqueous solution. A rule is followed usually, in deciding which metal
can replace the one already present in an aqueous solution.This is decided by a series or a table of elements called the Activity series. The
activity series is a list of elements organized according to their
tendency to react (their reactivity). The more readily an element reacts
with other substances, the greater is its activity.
A list of all the elements and their reactivity can be summarized in the form of a table.
|Reacts with cold water and acids,
reacts with oxygen, forming oxides.
|Reacts with steam,
(but not cold water) and acids,
reacts with oxygen, forming oxides
|Does not react with water;
reacts with acids, replacing hydrogen;
reacts with oxygen, forming oxides.
|Reacts with oxygen forming oxides.
forms oxides only indirectly.
The more active elements tend to be more stable as cations in an aqueous solution, than in the elemental form. If a more-active element, such as potassium, and a compound containing a less-active element, such as water, which contains hydrogen are brought together, the more reactive element will replace the less-active element in the compound, as shown below.
2K(s) + 2HOH(l) → 2KOH(s) + H2(g)
In the activity series elements are arranged in the order of their activity, with the most active element at the top. In general, an element can displace those below it from compounds in solution but not those above it.
In addition to predicting displacement reactions, the activity series can help predict some synthesis and decomposition reactions.In general,compounds of active metals are readily synthesized, but such compounds do not easily decompose to re-form the metal. On the other hand, compounds of less active metals decompose readily but are difficult to make.For example, the synthesis of potassium compounds from their elements can be carried out more easily than the synthesis of compounds of nickel or tin.
Along with predicting whether a reaction will occur, the activity series provides indications of how easily and quickly the reaction will proceed. In general, the farther apart two elements are on the activity series, the more likely it is that the higher one will quickly displace the lower one in compounds.
The Reactivity Series is a group of metallic elements listed, with the
reactive metals at the top and the non-reactive at the bottom.
Experiments involving displacement reactions have been summarized in activity series. An activity series is a list of metals arranged in order of decreasing
strength as reducing agents.
Metals above hydrogen in the activity
series displace hydrogen from acids and are termed active metals, metals
below hydrogen do not displace hydrogen from acids and are termed
The reactivity of metals can be completely understood from the activity series. Depending upon the group and the block, the metals belong to their reactivity can be summarized as follows.
Group 1: Alkali metals, such as sodium are very reactive as free metals and very nonreactive as ions. They always have an oxidation state of +1 in their compounds. The reactivity of the series increases as we go down from Lithium to Cesium.
Group 2: Alkaline earth metals, are less electropositive and less reactive than the alkali metals. The reactivity decreases as we move down from Beryllium, Be to Radium.
Group 3 to 12: The d block metals or the transition metals are less reactive than the alkaline earth metals and some even are found in free form in nature, like gold and silver.Lanthanides and actinides are f- block metals. Their reactivity is similar to that of transition elements.
Write a balanced chemical equation for the reaction that will occur if the metals copper and zinc are placed in a solution containing copper and zinc are placed in a solution containing copper (II) and zinc cations. Cu(s), Zn(s), Cu2+ (aq), and Zn2+ (aq) are present.
Solution1. Check the activity series for the more reactive metal:
Zinc is higher on activity table than copper. This means that zinc metal will form a zinc cation as the product, displacing the copper ion from the solution. So, the zinc metal and copper(II) ion will be the reactants.
Zn(s) + Cu2+ (aq) → Cu(s) + Zn2+(aq)2. Check other combinations of reactants for reactions:
The reaction of Cu with Cu2+ and the reaction of Zn and Zn2+ will not produce any new compounds. Furthermore, because Cu is lower then Zn on the activity series, it will not replace Zn ions. Thus, no other combination of reactants will result in a reaction.
Group 17 elements are highly reactive. The halogens are just one electron less than the noble gas configuration and so, they have similar reactivities. They are all very reactive. Their reactivity decreases comparatively, as we move down the group. The decreasing order of their reactivity can be shown as follows.
F > Cl > Br>I
So, fluorine can replace chlorine from its solution, and similarly, chlorine can replace Bromine, and so on.
Some Point about Activity Series of Non-Metals:
- Groups 13 to 16, the P- block elements contain all the non- metals. But, in the case of non metals, the reactivity is not as regular as the metals.
- Since, in each group, the metallic character increases as we move down a group, their reactivity shows an irregularity.
- Example: Group 13 starts with a non-metal, Boron, while all the other elements in this group are metals, Aluminium is very reactive metal. Bron is reactive, as a non metal.
- In group 15, though, nitrogen is not very reactive, while phosphorus exhibits many allotropes and is reactive.
- The Chalcogen group elements also show irregularity in their reactivity. Oxygen forms double bonds and is very reactive. Similarly, sulfur is also reactive, forming double bonds in some compounds.
- The noble gas elements, the 18th group are unreactive, except for xenon, which forms compounds with fluorine.