Introduction to NCERT Exemplar Solutions for Class 12 Chemistry Chapter 7: The P-Block Elements
The p-block elements form one of the most diverse and significant sections of the periodic table. These elements are located in groups thirteen to eighteen and include non-metals, metalloids, and metals. Because of their varied electronic configurations, oxidation states, and bonding tendencies, p-block elements display a wide range of chemical and physical properties. Chapter 7 of Class 12 Chemistry focuses on the p-block elements studied in Class 11 and extends into a deeper understanding of groups fifteen and sixteen in this unit. The NCERT Exemplar Solutions for this chapter provide comprehensive explanations of conceptual, descriptive, and numerical problems, enabling students to build mastery.
Group 15 Elements: Nitrogen Family
The group fifteen elements include nitrogen, phosphorus, arsenic, antimony, and bismuth. They have five valence electrons, giving them a general configuration of ns²np³.
-
Nitrogen, the first element, exists as a diatomic molecule with a strong triple bond, making it highly stable and relatively inert under normal conditions.
-
Phosphorus exists in several allotropes such as white, red, and black phosphorus.
-
Arsenic, antimony, and bismuth show increasing metallic character down the group.
Exemplar questions test the ability to explain trends in atomic size, ionization enthalpy, electronegativity, and reactivity. Students also practice writing balanced equations for the preparation and properties of important compounds like ammonia, nitric acid, and phosphorus oxoacids.
Important Compounds of Group 15
Key compounds include:
-
Ammonia: Used as a fertilizer and in the manufacture of nitric acid by the Ostwald process.
-
Nitric acid: A strong oxidizing agent with wide applications in explosives, fertilizers, and dyes.
-
Phosphorus oxoacids: Showing different oxidation states and bonding patterns.
Exemplar solutions often provide step-by-step reasoning for explaining the structure, hybridization, and bonding in these compounds.
Group 16 Elements: Oxygen Family
Group sixteen includes oxygen, sulfur, selenium, tellurium, and polonium. They have six valence electrons with a general electronic configuration of ns²np⁴.
-
Oxygen is the most abundant element on Earth and essential for life. It exists as a diatomic molecule in its natural state.
-
Sulfur shows several allotropes and forms many oxoacids and compounds such as sulfur dioxide and sulfur trioxide.
-
Selenium and tellurium are less reactive and have semi-metallic properties, while polonium is radioactive.
Exemplar questions encourage students to explain periodic trends in electronegativity, electron gain enthalpy, and bond strength. Numerical problems often involve balancing redox equations involving sulfur and oxygen compounds.
Important Compounds of Group 16
Key compounds include:
-
Dioxygen (O₂): Essential for respiration and combustion.
-
Ozone (O₃): A powerful oxidizing agent that protects life on Earth by absorbing harmful ultraviolet radiation.
-
Sulfur dioxide (SO₂): Used in bleaching, disinfecting, and as a preservative.
-
Sulfuric acid (H₂SO₄): An important industrial chemical, often called the “king of chemicals,” used in fertilizers, paints, and detergents.
Exemplar solutions give detailed reasoning for explaining the acidic and oxidizing properties of these compounds, along with structural diagrams and reactions.
Trends and Properties
Students study variations in properties such as atomic size, ionization enthalpy, oxidation states, and chemical reactivity within these groups. The tendency to exhibit catenation (the ability to form chains) is prominent in carbon and sulfur but decreases down the group. The inert pair effect, common in heavier elements like bismuth and polonium, is explained with examples. Chemistry Exemplar problems often include conceptual questions where students must compare the stability of different oxidation states or explain the anomalous behavior of nitrogen and oxygen compared to their heavier congeners.