Notes for R3.2.3 Reactivity of elements based on periodic trends - IB | RevisionDojo
R3.2.3 Reactivity of elements based on periodic trends Notes
Predicting Reactivity Trends in Metals and Halogens
Metals: The Ease of Oxidation
Metals are excellent reducing agents because they tend to lose electrons and form positive ions (cations) during chemical reactions.
But why do some metals lose electrons more readily than others?
This depends on their position in the periodic table and their intrinsic reactivity.
Group 1 Metals (Alkali Metals):
These metals are highly reactive because they have only one valence electron, which is easily lost.
Reactivity increases as you move down the group because the outermost electron is farther from the nucleus, experiencing weaker electrostatic attraction.
Other Metals:
For metals outside Group 1, their reactivity can be tested experimentally using displacement reactions.
A more reactive metal will displace a less reactive metal from its ionic solution.
Example
Zinc and Copper Displacement
When zinc metal is placed in a solution of copper(II) sulfate $ \text{CuSO}_4 $, the following reaction takes place: $$ \text{Zn}(s) + \text{Cu}^{2+}(aq) \rightarrow \text{Zn}^{2+}(aq) + \text{Cu}(s) $$
Here, zinc is oxidized to $ \text{Zn}^{2+} $ (it loses electrons), and copper(II) ions are reduced to copper metal (they gain electrons).
This demonstrates that zinc is more reactive than copper.
Common Mistake
Many students forget that a displacement reaction only occurs if the metal in solid form is more reactive than the metal in the ionic solution.
If the metal in solution is more reactive, no reaction will occur.
Halogens: The Ease of Reduction
Halogens, as non-metals, act as oxidizing agents because they readily gain electrons to form negative ions (anions).
However, their reactivity decreases as you move down Group 17 of the periodic table. Why does this trend occur?
Fluorine:
Fluorine is the most reactive halogen due to its small atomic radius and high electronegativity, which allow it to attract electrons very effectively.
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Question 1
Recap question
In the reaction
Zn(s)+Cu2+(aq)→Zn2+(aq)+Cu(s),
which species acts as the oxidizing agent?
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Why are metals considered reducing agents?
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Note
Reactivity and Displacement Reactions
The reactivity series is a list of elements ordered by their tendency to lose or gain electrons. This fundamental concept helps us understand why certain chemical reactions occur and others don't.
Oxidation is the loss of electrons, while reduction is the gain of electrons. Remember this with the acronym OIL RIG (Oxidation Is Loss, Reduction Is Gain).
A displacement reaction occurs when a more reactive element displaces a less reactive element from a compound.
AnalogyThink of the reactivity series like a sports ranking. Just as the top-ranked team can defeat any lower-ranked team, a more reactive element can displace a less reactive one.
ExampleWhen a piece of iron is placed in copper sulfate solution, iron displaces copper because iron is more reactive:
Fe(s)+CuSO4(aq)→FeSO4(aq)+Cu(s)
NoteReactivity is not just about violence or explosiveness; it's about the tendency to lose or gain electrons.
