   Chapter 21, Problem 28PS

Chapter
Section
Textbook Problem

The compound Na2O2 consists of (a) two Na+ ions and two O2− ions (b) molecules of Na2O2 (c) two Na+ ions and one O22− ion (d) Na2+ and O2− ions

Interpretation Introduction

Interpretation: To predict the ions in the compound Na2O2.

Concept introduction: Main group elements are categorized as s-block and p-block elements. The s-block elements include metals belonging to group 1A and group 2A and elements from group 3A to 8A are referred to as p-block elements. The reaction of the metals with the nonmetals forms ionic compounds.

Ionic compounds are formed by the loss of electrons from the metal which is gained by the nonmetals. The metal gets positively charge and the non-metal attains a negative charge thus forming cations and anions respectively. They do so to attain a noble gas configuration or to attain stability.

MMn++ne

Here, by losing electrons metal M achieve the noble gas configuration. These electrons are gained by the non-metals X as shown below.

X+neXn

The metals of group 1A form +1 ions because the highest oxidation number is always equal to the group number of that element. Thus, the charge on group 1A elements is +1. Similarly, group 2A elements form +2 ions by losing two electrons and have an oxidation number of +2. The non-metal gains these electrons to form anions with 1 and 2 charge.

Explanation

Reason for the correct option

Sodium belongs to group 1A of periodic table and has an oxidation number of +1. Thus, it loses one electron to attain noble gas configuration.

NaNa++e

The oxidation number of oxide ion is 2. So, the oxidation number of sodium in the compound Na2O2 is +2 which is incorrect as the highest oxidation number of sodium is +1. Thus, the compound contains two Na+ ions and one peroxide group O22

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