Classification of Elements and Periodicity in Properties

The s‑block elements, comprising the alkali metals (Group 1) and alkaline earth metals (Group 2), are characterized by having their outermost electrons in s‑orbitals—one in alkali metals (ns¹) and two in alkaline earth metals (ns²). These elements exhibit distinct physical and chemical properties due to their electronic configurations. Alkali metals, including lithium, sodium, potassium, rubidium, cesium, and francium, are highly reactive, soft, and have low melting and boiling points. They readily lose their single valence electron to form +1 cations, leading to vigorous reactions with water and non‑metals, producing basic oxides and hydroxides. Alkaline earth metals—beryllium, magnesium, calcium, strontium, barium, and radium—are harder, denser, and have higher melting and boiling points compared to alkali metals. They lose two valence electrons to form +2 cations, resulting in less reactive behavior. Their oxides and hydroxides are basic but less soluble and less thermally stable than those of alkali metals.

This Story also Contains

1. S-Block Elements: It's Arrangement and Classification
2. Solved Examples Based on S-Block Elements
3. Conclusion

Understanding the properties and trends of s‑block elements is crucial for various competitive exams. For instance, the JEE Main syllabus includes topics on the classification of elements and periodicity in properties, covering s‑block elements and their periodic trends. Similarly, the NEET syllabus encompasses the study of s‑block elements, focusing on their chemical properties and reactivity. The BITSAT exam also includes questions related to s‑block elements, assessing knowledge in inorganic chemistry. Additionally, the WBJEE syllabus covers the classification of elements and periodicity in properties, including the study of s‑block elements. Therefore, a thorough understanding of s‑block elements is essential for success in these examinations.

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.

Also Read:

• Metals, Non-metals And Metalloids

• Atomic Size & Atomic Radius

Recommended topic video on (Classification of Elements and Periodicity in Properties)

Solved Examples Based on S-Block Elements

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

1) 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) 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) 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) 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).

Practice more Questions from the link given below:

Conclusion

The s‑block elements, comprising alkali metals (Group 1A) and alkaline earth metals (Group 2A), are highly reactive due to their electronic configurations. Alkali metals possess a single valence electron, making them eager to form +1 ions, while alkaline earth metals have two valence electrons, forming +2 ions. These elements play vital roles across various industries. In metallurgy, magnesium alloys are used in lightweight structures, and calcium aids in metal extraction. In agriculture, potassium and calcium are essential in fertilizers and soil conditioning. Pharmaceutical applications include magnesium hydroxide as an antacid and calcium supplements for bone health.