Classification of Elements and Periodicity in Properties

Edited By Shivani Poonia | Updated on Sep 23, 2024 01:05 PM IST

Introduction

In the periodic table, the s-block elements comprise two groups situated on the leftmost side: Alkali metal group 1 and the alkaline earth metal group 2. These are considered elements whose outermost electrons are in s-orbitals, and may therefore differently chemically behave themselves. The alkali metals are lithium, sodium, and potassium, and they are very reactive because they moderately lose one electron in a reaction with non-metals to attain the nearest noble inert gas configuration. The alkali metals are highly reactive metals from Group IA that readily lose their 1s electron to form +1 ions: lithium, sodium, potassium, rubidium, caesium and francium For example, the alkaline earth metals such as magnesium, calcium, and barium though less reactivity compared with alkali metals are highly reactive with forming basic oxides and hydroxides.

In this article, we will cover the concept of the Classification of s-block elements. This concept falls under the broader category of Classification of Elements and Periodic Table, which is a crucial chapter in Class 11 chemistry. It is not only essential for board exams but also for competitive exams like the Joint Entrance Examination (JEE Main), National Eligibility Entrance Test (NEET), and other entrance exams such as SRMJEE, BITSAT, WBJEE, BCECE, and more. Over the last ten years of the JEE exam (from 2013 to 2023), one question has been asked on this concept, in 2021 from this concept.

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This Story also Contains

Introduction
S-Block Elements: It's Arrangement and Classification
Solved Examples Based on S-Block Elements
Conclusion

Classification of Elements and Periodicity in Properties

S-Block Elements: It's Arrangement and Classification

The elements having ns¹ and ns² electronic configurations in their outermost shell are called s-block elements.
Elements with ns¹ configuration are called group 1 (alkali elements).
Elements with ns² configuration are called group 2 (alkaline earth elements).
They are highly reactive and readily form univalent or bivalent positive ions by losing the valence electrons.
The elements of this block are soft, malleable and good conductors of heat and electricity.
The elements have the largest atomic and ionic radii but the lowest ionization energies.
They show fixed valency and oxidation states.
The loss of the outermost electrons(s) occurs readily to form M⁺ (in the case of alkali metals) or M²⁺ ions (in the case of alkaline earth elements).
Except for beryllium compounds, all other compounds of this block element are predominantly ionic.
They are soft metals, having low melting points and boiling points.
These metals and their salts impart characteristic colour to the flame. For example, sodium salt imparts a golden yellow colour to a flame.
The elements of this group have large size, strong reducing nature, high electropositive nature, very low electronegativity values, ionization energy and electron affinity.

Solved Examples Based on S-Block Elements

Example 1: The element Ba with atomic number 56 belongs to which block:

1) (correct) s-block

2) p-block

3) d-block

4) f-block

Solution: The electronic configuration of Ba is 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶4d¹⁰5s²5p⁶6s². Thus, the outermost electrons of Ba enter into the s-orbital. Hence, Ba belongs to the s-block.

Therefore, Option(1) is correct

Example 2: The electronic configuration of element A is 1s²2s²2p⁶3s² and of B is 1s²2s²2p⁵. The formula of the compound is:

1) AB

2) A₂B

3) (correct)AB₂

4) A₂B₃

Solution: The outermost electrons of any element determine the valency of the element. Thus valency of A is 2 and that of B is 1. Thus, the formula of the compound is AB₂.

Therefore, Option(3) is correct.

Example 3: Elements which have the outermost electronic configuration are known as:

1) alkali metal

2) alkaline metals

3) (correct) Both a and b

4) chalcogens

Solution: S- Block elements - The elements of group 1 (alkali metal) and elements of group 2 (alkaline metal) which have ns¹ and ns² configurations belong to s-block elements.

The elements of group 1 and group 2 are known as alkali metals and alkaline earth metals respectively.

Hence, the answer is the option (3).

Example 4: Valency shown by s-block elements:

1) +1

2) +2

3)-1

Solution: Valency of S-Block elements -

They have the common group valency of +1 and +2 for group 1 and group 2 respectively.

S-block elements have +1 and +2 valencies.

Hence, the answer is the option (4).

Example 5: Which one of these elements is malleable, ductile, and is a good conductor of heat and electricity?

1) (correct) K

2) C

3) Br

4) Se

Solution: The physical property of S-Block elements -

1. They are malleable and ductile.

2. Good conductors of heat and electricity.

S-block elements have these properties.

Among them, only K belongs to alkali metals

Hence, the answer is the option (1).

Conclusion

Thus, the members of s-block elements that include the elements in group I A (the alkali metals) and group II A (the alkaline earth metals) of the periodic table have different features in chemical reactivity in chemical applications. Alkali metals are highly reactive because they are willing to lose the one electron in their highest occupied energy level to forge Ions with non-metals while alkali earth metals are less reactive, but they also get involved in chemical reactions to attain their nearest stable configuration. These elements have important use in different industries and the following are some of them: metallurgical industry, agricultural industry and pharmaceutical industry. They include the formation of alloys, reaction with water to form hydroxides and opposition of diverse biological processes to fame their usability in daily life and research.