The S-Block-Elements

The s-Block Elements

Welcome to the chapter on The s-Block Elements for Class 11. In this chapter, you will learn about the elements in the s-block of the periodic table, their properties, trends, and important compounds. By the end of this chapter, you will understand the chemistry of alkali and alkaline earth metals and their significance in daily life and industry.

Introduction

The s-block elements are found in Groups 1 and 2 of the periodic table. They include alkali metals (Group 1) and alkaline earth metals (Group 2). These elements have their outermost electrons in the s-orbital.

Position in the Periodic Table

• Group 1 (Alkali Metals): Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs), Francium (Fr)
• Group 2 (Alkaline Earth Metals): Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), Radium (Ra)

Electronic Configuration

• General configuration: ns¹ for Group 1, ns² for Group 2
• s-orbital is being filled

Physical Properties

• Soft (especially alkali metals), low density (Li, Na, K float on water)
• Good conductors of heat and electricity
• Low melting and boiling points (decrease down the group for alkali metals)
• Shiny appearance when freshly cut

Chemical Properties

• Highly reactive, especially alkali metals
• Form ionic compounds
• React with water to form hydroxides and hydrogen gas (Group 1 more vigorous than Group 2)
• React with halogens to form salts

Trends in Properties

• Atomic and ionic size increases down the group
• Ionization enthalpy decreases down the group
• Electronegativity decreases down the group
• Reactivity increases down the group for alkali metals, but decreases for alkaline earth metals

Important Compounds

• Sodium chloride (NaCl): Common salt, used in food
• Sodium hydroxide (NaOH): Caustic soda, used in soap making
• Calcium carbonate (CaCO₃): Found in chalk, limestone, marble
• Magnesium sulfate (MgSO₄): Used in medicine (Epsom salt)

Uses of s-Block Elements

• Sodium and potassium are essential for nerve function in the body
• Calcium is important for bones and teeth
• Magnesium is used in fireworks and medicines
• Lithium is used in batteries

Practice Questions

1. Name any two alkali metals and two alkaline earth metals.
2. Write the general electronic configuration of s-block elements.
3. Why are alkali metals stored under oil?
4. What happens when sodium reacts with water?
5. List two uses of calcium.

Challenge Yourself

• Explain why the reactivity of alkali metals increases down the group.
• Describe the difference between the reactions of magnesium and sodium with water.

Did You Know?

• Francium is the rarest naturally occurring element in the s-block.
• Magnesium burns with a bright white flame and is used in fireworks.

Glossary

• s-block: The block of elements in the periodic table where the outermost electrons enter the s-orbital.
• Alkali metals: Group 1 elements (Li, Na, K, Rb, Cs, Fr).
• Alkaline earth metals: Group 2 elements (Be, Mg, Ca, Sr, Ba, Ra).
• Ionization enthalpy: The energy required to remove an electron from an atom.

Answers to Practice Questions

1. Alkali metals: Sodium (Na), Potassium (K); Alkaline earth metals: Calcium (Ca), Magnesium (Mg)
2. Group 1: ns¹; Group 2: ns²
3. Because they react vigorously with air and water.
4. Sodium reacts with water to form sodium hydroxide and hydrogen gas, producing heat and sometimes fire.
5. Calcium is used for making cement and is important for bones and teeth.

---

Understanding s-block elements helps you learn about the building blocks of matter and their role in daily life!