JEE Main Chemistry S Block Elements: Key Concepts and Reactions

The S Block Elements are an important part of the JEE Mains syllabus, often featuring questions that test students on their understanding of periodic trends, chemical properties, and practical applications. These questions are typically straightforward, making this chapter a scoring area for aspirants aiming to boost their ranks.

In this chapter, the focus is on alkali metals (Group 1 IA Elements) and alkaline earth metals (Group 2 Group IIA Elements), known for their high reactivity and diverse applications in real life and industry. Students will learn atomic structure, reactions, and periodic properties. With Vedantu’s expert guidance and S Block Elements PDF resources, understanding these fundamental concepts becomes simpler, helping students approach related questions in JEE Mains confidently

General Characteristics of s-block Elements

1. The general characteristics of alkali metals (Li, Na, K, Rb, Cs and FrY and alkaline earth metals (Be, Mg, Ca, Sr, Ba and Ra), i.e. s-block elements are as mentioned below:

2. They are soft metals, possess low melting and boiling points, have the largest atomic radii in their corresponding periods and are good conductors of heat and electricity.

3. They have low values of ionization energies and are hence highly electropositive.

4. They are very reactive and readily form ionic compounds. They show a fixed valency which depends on the number of electrons present in the outermost shell. The alkali metals show monovalency while alkaline earth metals show divalency. They are never found in a free state in nature due to their reactive nature.

5. On account of low ionization energies and highly negative electrode potentials, they act as strong reducing agents. The alkali and alkaline earth metals cannot be prepared by doing electrolysis of aqueous solutions of their salts.

6. Except for Be and Mg, they impart a characteristic colour to the flame.

7. The compounds of s-block elements are predominantly ionic and colorless. However, lithium and beryllium compounds are covalent in nature.

8. They have a great affinity for oxygen and nonmetals. The oxides are basic. The hydroxides are strong alkali.

9. They displace hydrogen from acids and form corresponding salts.

10. With the exception of Be and Mg, they decompose water and readily evolve hydrogen.

S Block Elements Properties: Physical and Chemical

The modern periodic table is the outcome of different models of tables developed by scientists across the centuries. This format is based on Mendeleev’s periodic table, which originated in 1869. Since then, the world of chemistry has transformed. We got a better understanding of the behaviour of the elements. In this section, we will study the s block elements that lie on the Group IA and IIA of the modern periodic table. Here, we will precisely study the physical and chemical properties of periodic table s block elements.

What are S Block Elements?

You have studied that every element has a distinguishable electronic configuration that determines its physical and chemical properties. This electronic configuration is the prime factor that helps us to define and arrange the modern periodic table. The first two groups (columns) that are Group IA and Group IIA contain the alkali metals and alkaline earth metals respectively. In this segment, we will study the s block periodic table groups and the characteristics of the elements.

As mentioned earlier, the metals in the first group are called alkali metals. The second group contains alkaline earth metals. The term ‘s block’ has been given to those elements whose valence shell electronic configuration is restricted within the S-suborbital. As the maximum capacity of this suborbital is 2, we will only get two groups. All the elements with valence shell configuration ns1 and ns2 are called s-block elements.

Properties of s Block Elements

• The total number of s block elements is 14 (Group IA and IIA).

• The elements are soft with low boiling and melting points.

• Due to the bigger size of the atomic radii of the periodic table s block elements, they possess low ionization potential and behave as highly electropositive elements.

• These elements in the s block periodic table are highly reactive and readily form compounds showing fixed valency (1 or 2).

• These elements are strong reducing agents due to their high negative electrode potential value.

• Other than magnesium and beryllium, all elements have a characteristic flame colour and readily react with water to form alkalis and release hydrogen.

The Melting Point of S-Block Elements

The melting point of s-block elements is the temperature at which they change from a solid to a liquid. The melting point of s-block elements decreases as you go down the group. This is because the outer electrons of the atoms become less tightly bound as you go down the group. This makes it easier for the atoms to move around and become a liquid.

The melting point of s-block elements is also affected by the size of the atom. The larger the atom, the lower the melting point. This is because the larger atoms have more electrons to share, which makes the bonds between the atoms weaker.

The melting points of s-block elements are important for a number of reasons. For example, they are used in the production of metals and alloys. They are also important in the design of electrical circuits and other electronic devices.

Here is a table of the melting points of s-block elements:

Electronic Configuration of S Block Elements

This table shows how the s-orbital is filled in these elements, with Group 1 having one electron and Group 2 having two electrons in their outermost s-orbital.

Atomic Mass of S Block Elements

S-block elements are the elements in the first two columns of the periodic table. They are also known as alkali metals and alkaline earth metals. S-block elements have the lowest atomic numbers and are characterized by their valence electrons, which are located in the s-orbital.

The atomic mass of an element is the total mass of all the protons and neutrons in an atom of that element. The atomic mass is usually expressed in atomic mass units (amu) or grams per mole (g/mol).

The atomic masses of s-block elements change across a period and down a group. In a period, the atomic mass of an element increases as the atomic number increases. This is because the number of protons in the nucleus increases as the atomic number increases. The number of neutrons in the nucleus also increases, but not always by the same amount. The increase in the number of protons and neutrons in the nucleus causes the atomic mass of the element to increase.

Down a group, the atomic mass of an element also increases. This is because the number of electron shells in an atom increases as the atomic number increases. The number of electrons in the atom also increases. The increase in the number of electron shells and electrons in the atom causes the atomic mass of the element to increase.

The following table shows the atomic masses of the s-block elements:

Interesting Facts about Atomic Masses of S-Block Elements:

• The lightest s-block element is lithium and the heaviest s-block element is francium.

• The atomic masses of s-block elements vary depending on the number of isotopes of each element. An isotope is a form of an element that has a different number of neutrons in its nucleus.

• The atomic masses of s-block elements are important for understanding the chemical properties of these elements. For example, the reactivity of an s-block element is inversely proportional to its atomic mass. This means that the lighter the s-block element, the more reactive it is.

What are Alkali Metals?

The elements included in the Group IA due to their ns1 valence shell electronic configuration are called alkali metals. These s block elements have the biggest atomic radii in the period as the number of electrons is the lowest among all the periodic members. Here is the list of the physical and chemical properties of alkali metals.

• As the characteristics of s block elements mentioned earlier, alkali metals are also soft and solids of silvery-white color.

• Except for lithium, you can cut these metals with a knife.

• Group IA elements have the largest atomic radii due to the lack of electrons in the shells. Hence, these elements have the lowest ionization potential. They react with water to form respective alkalis in water. Due to these characteristics of s block elements, they are called alkali metals.

• Due to the presence of one electron in the outermost valence shell, the lattice energy of the crystals is also very low resulting in low melting and boiling points.

• Due to low ionization potential, these metals easily lose the outermost electron to form M+ ions in a solution.

• The electronegative character increases when you go down the group.

• These s block elements are called good conductors of electricity and heat due to the loosely-bound electrons present in the outermost shells. They can easily move due to low ionization energy levels.

• Alkali metals are also good reducing agents. The strongest is Cesium and the weakest is Lithium.

What are Alkaline Earth Metals?

These elements belonging to the Group IIA in the s block NCERT are called alkaline earth metals. They have an ns2 valence electronic configuration. It means that they have two electrons in the outermost shell. This is why the only element in this group which is nonmetal and inert is Helium (Group 8A). The characteristics of s block elements in points are:

• There are 6 elements in this group (Be, Mg, Ca, Sr, Ba, and Ra). The only element that is non-reactive or inert is Helium (Group 8A).

• These elements are quite reactive and always occur in a combined state. In fact, they are denser than alkali metals. Due to their existence as oxides in the earth, these s block element names are called alkaline earth metals.

• The melting and boiling points are higher than the previous alkali metal existing in the same period.

• The 1st and 2nd ionization energies reduce from Beryllium to Barium. In fact, the 1st ionization energy is half the 2nd ionization energy.

Differences between Alkali (Group IA) and Alkaline Earth Metals (Group IIA)

According to the s block elements definition, the alkali metals have 1 electron in the valence shell whereas the alkaline earth metals have 2 electrons. Hence, the alkali metals are mono-valent and the alkaline earth metals are bivalent. Alkali metals are more electropositive than alkaline earth metals.

The Main Points of Difference Between Alkaline Earth Metals and Alkali Metals are Given Below

Periodic Trends in the S-Block Elements

The properties of the s-blocks elements can be predicted with the help of the periodic trends in the modern periodic table. These periodic trends are the patterns in the properties of the elements. The explanation of these periodic trends are discussed below:

• Atomic Radius - In the s-block elements, the size of the alkali metals is larger as compared to other metals. The number of electrons increases with an increase in the atomic number. Therefore, down the group the atomic radius of elements increases. Across the period, this radius decreases.

• Ionisation Enthalpy - Down the group the size of the metal increases which result in the decrease of the force of attraction between nucleus and electrons. Due to this, the ionisation enthalpy decreases down the group. from left to right, the ionisation enthalpy increases.

• Electron Affinity - As the size increases down the group, thus, the electron affinity is decreased. Across the period, this property of elements increases.

• Electronegativity - The periodic trend of this property is that the electronegativity of the s-block elements decreases from top to bottom and increases from left to right. 

• Electropositivity - There is an increment in this property down the group and decrement across the period. 

• Metallic Nature - In the s-block elements, the metallic character of the elements increases from top to bottom and decreases from left to right.

• Non-metallic Nature - The non-metallic nature of the elements decreases down the group and increases across the period. 

Diagonal Relationship between the Elements Of S-Block

The diagonal relationship exists between the adjacent elements placed diagonally in the second and the third period of the periodic table. These pairs of elements show similar properties. The diagonal relationship arises because of the identical size of the ions. The elements which show similar properties are known as diagonal neighbours or diagonal pairs. The elements of the s-block which show a diagonal relationship are:

• Lithium (Group IA and second period) and Magnesium (second group and third period)

• Beryllium (second group and second period) and Aluminium (third group and third period)

• Lithium and magnesium are considered the hardest elements as compared to other elements. 

• Lithium and magnesium chlorides are soluble in an organic solvent like ethanol.

• These elements are light in weight.

• The reaction of lithium and magnesium with water is not so vigorous. 

• The hydroxides and oxides of these elements are less soluble. 

• Lithium and magnesium form nitrides in the presence of nitrogen.

• There is no formation of superoxides when lithium and magnesium react with an excess of oxygen.  

•  The formation of carbon dioxide and its oxides takes place when carbonates of lithium and magnesium are heated. 

Similarities Between Beryllium and Aluminium Hydroxide of S Block Elements

• Beryllium and aluminium hydroxide form ions when they react with excess alkali.

• Both the elements can withstand the acid attack as they can form the oxide film. 

• The elements can form complexes.

• The chlorides of both elements are soluble in organic solvents.

Preparation and Properties of Important Compounds: Sodium Carbonate, Sodium Hydroxide, and Sodium Hydrogen Carbonate

Sodium Carbonate ($Na_2CO_3$):

Sodium carbonate, commonly known as soda ash or washing soda, is prepared through the Solvay process or the Leblanc process.

Solvay Process: This method involves the reaction between sodium chloride (NaCl) and ammonia ($NH_3$) to form sodium bicarbonate ($NaHCO_3$), which is then converted to sodium carbonate.

Properties: Sodium carbonate is a white crystalline powder. It is alkaline in nature and is used in industries for various purposes, including glass manufacturing and water softening.

Sodium Hydroxide (NaOH):

Sodium hydroxide, often called caustic soda, is produced through the chlor-alkali process. This process involves the electrolysis of brine (sodium chloride solution).

Properties: Sodium hydroxide is a strong base and is highly caustic. It is used in the production of soap, paper, and various chemical processes, including the saponification of fats and oils.

Sodium Hydrogen Carbonate ($NaHCO_3$):

Sodium hydrogen carbonate, also known as baking soda, can be synthesized by saturating a solution of sodium carbonate with carbon dioxide.

Properties: Sodium hydrogen carbonate is a white crystalline powder. It has a slightly alkaline property and is used in baking, as an antacid, and for fire extinguishing.

Industrial Uses of Lime, Limestone, Plaster of Paris, and Cement

Lime (CaO):

Lime is primarily produced by heating limestone ($CaCO_3$) in a kiln, a process called calcination.

Industrial Uses: Lime has various applications, including as a flux in metallurgy, in the production of calcium carbide, in water and wastewater treatment for pH control, and as a building material in the form of mortar and plaster.

Limestone ($CaCO_3$):

Limestone is a sedimentary rock consisting mainly of calcium carbonate.

Industrial Uses: Limestone is used as a raw material in the production of cement and concrete. It is also employed as a flux in the iron and steel industry, for making glass, and in agriculture as a soil conditioner.

Plaster of Paris ($CaSO_4\cdot2H_2O$):

Plaster of Paris is prepared by heating gypsum ($CaSO_4\cdot2H_2O$) to remove water molecules.

Industrial Uses: Plaster of Paris is widely used in the construction industry for making casts, molds, and wall plaster. It is also utilized in the medical field for orthopedic casts.

Cement:

Cement is manufactured by grinding clinker, a mixture of limestone, clay, and other materials, to a fine powder.

Industrial Uses: Cement is a primary binding material used in the construction industry. It is essential for making concrete, which is the foundation of most building projects.

Biological Significance of Sodium (Na), Potassium (K), Magnesium (Mg), and Calcium (Ca)

Sodium (Na):

Sodium is a vital electrolyte in biological systems and plays a crucial role in maintaining osmotic pressure and regulating fluid balance within cells and the extracellular environment.

Sodium ions ($Na^+$) are essential for nerve impulse transmission and muscle contraction.

Potassium (K):

Potassium is another essential electrolyte that is crucial for maintaining proper muscle and nerve function.

It also helps regulate the body's pH and is involved in cell membrane potential and heart rhythm.

Magnesium (Mg):

Magnesium is essential for various biochemical reactions in the body, including those related to energy metabolism and DNA synthesis.

It plays a key role in muscle and nerve function, as well as bone health.

Calcium (Ca):

Calcium is a structural component of bones and teeth, providing strength and rigidity.

It is involved in muscle contraction, blood clotting, and signalling processes within cells.

Conclusion

The study of S Block Elements is of paramount importance for JEE Main aspirants. These elements, including alkali metals and alkaline earth metals, exhibit unique properties and reactivity patterns that are integral to the understanding of chemistry. The S Block provides a foundational knowledge of periodic trends, chemical bonding, and the behaviour of metals and their compounds. This knowledge is not only crucial for acing the JEE Main but also forms the basis for comprehending a wide array of chemical reactions and their industrial applications. So, a strong grasp of S Block Elements is the key to mastering the world of chemistry and excelling in the JEE Main examination.

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