   Chapter 21, Problem 9PS

Chapter
Section
Textbook Problem

Select one of the alkali metals, and write a balanced chemical equation for its reaction with chlorine. Is the reaction likely to be exothermic or endothermic? Is the product ionic or molecular?

Interpretation Introduction

Interpretation: Balanced chemical equation of an alkali metal with chlorine.

Concept introduction: Alkali metals belong to group 1A of the periodic table. It consists of elements lithium, sodium, potassium, rubidium, cesium and francium. All of them have one electron in their outermost shell. They are all metals and tend to lose their valence electron. Thus, they have +1 oxidation number.

Alkali metals are very reactive and form compounds with chlorides, oxides and water. Alkali metals combine with non-metals and there is a transfer of electrons from metals to non-metals and thus ions are formed where metals have a positive charge and non-metals are negatively charged. Thus, alkali metals generally form ionic compounds and react vigorously to produce compounds with non-metals.

The reaction of alkali metals with non-metals produces energy which is released in the form of heat or light. Such reactions, in which energy is released in the form of heat and light are referred to as exothermic reactions. The reaction in which energy is absorbed from the surroundings are known as endothermic reactions.

In general, combination reaction is always exothermic in nature. Thus, exothermic reaction gives off energy and endothermic reactions absorb energy.

In order to have a balanced chemical equation, the atoms on both the product and reactant side of a combination reaction should be same. Thus, the stoichiometric coefficients are multiplied with the compounds in the chemical equation to have an equal number of atoms on both sides of the equation.

Explanation

The alkali metal selected is sodium.

The electronic configuration of sodium is [Ne]3s1. It has one valence electron in its outermost shell. It loses this electron to form monoatomic ion Na+ which has a noble gas configuration.

The electronic configuration of chlorine is [Ne]3s23p5. It has five valence electron in its outermost shell. Chlorine gains one electron to form monoatomic ion Cl which has a noble gas configuration.

Thus, the oxidation number of sodium ion is +1 and chloride ion is 1. Hence, the compound formed on combination of sodium with chlorine is NaCl

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