   Chapter 21, Problem 29PS

Chapter
Section
Textbook Problem

Write equations for the reaction of sodium with each of the halogens. Predict at least two physical properties that are common to all of the alkali metal halides.

Interpretation Introduction

Interpretation: The reaction of sodium with halogens is to be stated and two physical properties of alkali metal halides is to be predicted.

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.

Halogens belong to group 7A of the periodic table. It consists of elements fluorine, chlorine, bromine and iodine. The symbol X is used for halogens. They have five valence electrons in the outermost shell and gain one electron to attain noble gas configuration. The oxidation number of halides is 1.

Alkali metals are very reactive and form compounds with chlorides, oxides and water. Alkali metals combine with halogens and there is a transfer of electrons from the metal to halogens and thus ions are formed where metal has a positive charge and halogens are negatively charged. Thus, alkali metals react vigorously with halogens to form alkali metal halides.

Explanation

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 halogens is [Noble gas]ns2np5. It has five valence electron in its outermost shell. Halogens gain one electron to form monoatomic ion X which has a noble gas configuration.

Thus, the oxidation number of sodium ion is +1 and halide ion is 1. Hence, the compound formed on a combination of sodium with halogens is NaX.

The chemical equation for the reaction of sodium and halogens is:

2Na(s)+F2(g)2NaF(s)

The chemical equation for the reaction of sodium and chlorine is:

2Na(s)

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