Book cover for Objective Chemistry for Engineering and Medical Entrance Examinations

Objective Chemistry for Engineering and Medical Entrance Examinations

K Rama Rao

ISBN #9789332541771

1st Edition

2,463 Questions

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12,716 Students Helped

Homework Questions

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Summary
Learning Objectives
Key Concepts
Example Problems
Explanations
Common Mistakes

Summary

Group IA alkali metals are characterized by their single electron in the outer s orbital, which makes them extremely reactive, especially with water, where they form strong bases. Sodium stands out as the most abundant alkali metal, while cesium is less common and francium is rare and radioactive. These properties not only explain their chemical behavior but also highlight their varying roles in both natural processes and industrial applications.

Learning Objectives

1

Describe the electronic configuration (ns1) of Group IA alkali metals.

2

Explain the high reactivity of alkali metals, especially their reaction with water.

3

Identify the occurrence and abundance differences among sodium, cesium, and francium.

4

Understand the formation of strong bases when alkali metals react with water.

Key Concepts

CONCEPT

DEFINITION

Group IA Alkali Metals

Elements in the first column of the periodic table that have one electron in their outermost shell (ns1) and are highly reactive.

ns1 Electronic Configuration

Describes the electronic configuration of alkali metals where one electron occupies the s-orbital of the outer shell, making it loosely bound and easily lost.

Reactivity with Water

The vigorous reaction of alkali metals with water, resulting in the formation of strong bases (metal hydroxides) and the release of hydrogen gas.

Sodium

One of the Group IA alkali metals; the most abundant among them and widely used in various chemical applications.

Cesium

An alkali metal that is less abundant compared to sodium; known for its high reactivity and lower natural occurrence.

Francium

A radioactive alkali metal that is rare and is noted for its instability due to its radioactivity.

Example Problems

Example 1

Sodium reacts with water less vigorously than potassium because (1) it has higher atomic weight (2) it is less electropositive (3) it is more electronegative (4) it is a metal

Example 2

$\Lambda$ colourkss salt gives violet colour to Bunsen flame and also turns moist litmus paper to blue. It is (1) $\mathrm{Na}_{2} \mathrm{CO}_{3}$ (2) $\mathrm{KNO}_{3}$ (3) $\mathrm{K}_{2} \mathrm{CO}_{3}$ (4) $\mathrm{Cu}(\mathrm{OH})_{2}$

Example 3

Sodium has $\ldots \ldots \ldots \ldots \ldots \ldots .$ as compared to potassium. (1) less clectroncgativity (2) more ionisation potential (3) large atomic radius (4) lowcr melting point

Example 4

The least density is for (1) $\mathrm{Na}$ (2) $\mathrm{K}$ (3) $\mathrm{Rb}$ (4) Cs

Example 5

The electronic configuration of elements $X, Y, Z$ and $\mathrm{J}$ are given below. Which element has the highest metallic character? (1) $\mathrm{X}=2,8,4$ (2) $\mathrm{Y}=2,8,8$ (3) $Z=2,8,8,1$ (4) $\mathrm{J}=2,8,8,7$
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Step-by-Step Explanations

QUESTION

Why are Group IA alkali metals highly reactive, especially in reactions with water?

STEP-BY-STEP ANSWER:

Step 1: Recognize that alkali metals have an ns1 electronic configuration, which means they have a single valence electron.
Step 2: Understand that this lone valence electron is weakly held due to the low effective nuclear charge, making it easily lost.
Step 3: When alkali metals come into contact with water, the easily lost electron facilitates a rapid reaction, where the metal ionizes and water is reduced.
Step 4: This reaction produces a metal hydroxide (a strong base) and liberates hydrogen gas, often with great vigor.
Final Answer: The combination of the ns1 configuration and the weak bonding of the valence electron in alkali metals accounts for their high reactivity with water.

Reactivity of Alkali Metals

QUESTION

How do the abundance levels of sodium, cesium, and francium differ and why are these differences significant?

STEP-BY-STEP ANSWER:

Step 1: Identify that sodium is the most abundant alkali metal, making it common in natural compounds and industrial uses.
Step 2: Note that cesium is less abundant compared to sodium, which affects its availability and utility.
Step 3: Emphasize that francium is rare and radioactive, implying it is not found in large amounts naturally and has limited practical applications.
Final Answer: The differences in abundance among Group IA metals highlight their varying roles in natural processes and industrial applications, with sodium being prevalent, cesium less so, and francium being extremely scarce and radioactive.

Abundance of Group IA Metals

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Common Mistakes

  • Believing that alkali metals are found free in nature; in reality, they are typically encountered in compound forms due to their high reactivity.
  • Confusing the reactivity of alkali metals with that of other metal groups; the unique ns1 configuration specifically contributes to their vigorous reaction with water.
  • Overlooking the significance of abundance differences among Group IA metals, which affect their practical applications and natural occurrence.
  • Assuming that all alkali metals are safe to handle in their metallic form; special precautions are necessary due to their rapid reactions and, in the case of francium, radioactivity.