Question

How many elements in period 3 are highly reactive?

Answer 1

Reactivity is the tendency of a substance to undergo chemical reaction, either by itself or with some other materials to release energy. An element is said to be reactive if it fairly undergoes chemical reaction by either the process of oxidation or reduction.

Complete step-by-step answer: Period $3$ in a periodic table consist of Eight elements. these elements are Sodium $\left( Na \right)$, Magnesium$\left( Mg \right)$, Aluminum $\left( Al \right)$, Chlorine $\left( Cl \right)$, silicon $\left( Si \right)$, Phosphorus $\left( P \right)$, Sulphur $\left( S \right)$ and argon $\left( Ar \right)$.
Among these elements we know that argon is a noble gas and thus it has its complete octet. As a result of which it does not have any tendency to either donate or gain the electron. Being the most stable among all the elements, it is least reactive or non-reactive.
Sodium and magnesium including aluminum are strongly reducing species whereas on the other hand Chlorine, sulfur, Phosphorus, silicon behave as oxidizing species.
Let us see the chemical reactivity of all these elements: all these reactions are highly vigorous and the elements react rapidly as they are highly reactive elements.
1. Sodium: Some of the highly reactive reaction of sodium is listed below
With Base: $2Na\left( s \right)+2{{H}_{2}}O\to \,2NaOH\left( aq \right)+\,{{H}_{2}}\left( g \right)$
With acids: $2Na+{{H}_{2}}S{{O}_{4}}\to 2N{{a}^{+}}+S{{O}_{4}}^{2-}+{{H}_{2}}$
With halogens: $2Na+{{F}_{2}}\to NaF$
$2Na+C{{l}_{2}}\to 2NaCl$
With water: $2Na+2{{H}_{2}}O\to 2NaOH\,+{{H}_{2}}$
2. Magnesium
With acids: $Mg+{{H}_{2}}S{{O}_{4}}\to M{{g}^{2+}}+S{{O}_{4}}^{2-}\,+{{H}_{2}}$
With halogens: $Mg+C{{l}_{2}}\to MgC{{l}_{2}}$
With water: $Mg+2{{H}_{2}}O\to \,Mg{{\left( OH \right)}_{2}}\,+\,{{H}_{2}}$
Magnesium does not react with dilute aqueous alkalis.
3. Aluminum
With halogens: $2Al+3C{{l}_{2}}\to 2AlC{{l}_{3}}$
With acids: $2Al+\,3{{H}_{2}}S{{O}_{4}}\to 2A{{l}^{3+}}\,+\,2S{{O}_{4}}^{2-}+3{{H}_{2}}$
With base: $2Al+2NaOH+6{{H}_{2}}O\to 2N{{a}^{+}}+\,2{{\left[ Al{{\left( OH \right)}_{4}} \right]}^{-}}+3{{H}_{2}}$
4. Reactivity of chlorine, sulfur, phosphorus, silicon
With water: $C{{l}_{2}}+{{H}_{2}}OOC{{l}^{-}}+2{{H}^{+}}+C{{l}^{-}}$
Sulphur does not react with water under normal conditions.
The surface of lumps of silicon is protected by a very thin layer of silicon dioxide. This renders silicon more or less inert towards water.
With halogens: $C{{l}_{2}}+{{F}_{2}}\to 2ClF$
${{S}_{8}}+24{{F}_{2}}\to 8S{{F}_{6}}\,\left( orange \right)$
${{P}_{4}}+6{{F}_{2}}\to 4P{{F}_{3}}$
$Si+2{{F}_{2}}\to Si{{F}_{4}}$
With bases: $3C{{l}_{2}}+6O{{H}^{-}}\to Cl{{O}_{3}}^{-}+5C{{l}^{-}}+3{{H}_{2}}O$
${{S}_{8}}+\,6KOH\to 2{{K}_{2}}{{S}_{3}}+{{K}_{2}}{{S}_{2}}{{O}_{3}}+3{{H}_{2}}O$
$Si+4NaOH\to {{\left[ Si{{O}_{4}} \right]}^{4-}}+4N{{a}^{+}}+2{{H}_{2}}$

Note: In chemistry an element is said to be reactive and undergoes the chemical reaction if it wants to attain the stability. Already stable elements are not reactive such as the noble gases as they are already in their most stable states. So, the primary reason for being reactive is to attain stability.