Class 11 Chemistry Chapter 1 Handwritten Notes – Some Basic Concepts of Chemistry

Class 11 Chemistry Notes

Chapter 1 – Some Basic Concepts of Chemistry

1. Introduction

Chemistry is the branch of science that studies the composition, structure and properties of matter. It is called the Central Science because it connects physics, biology and environmental science.

• Health and Medicine: Development of life-saving drugs like Cisplatin and Taxol (Cancer therapy) and AZT (AIDS).
• Industry – Plastics, polymers and dyes,Synthesis of polymers, dyes, soaps, detergents, alloys, and new materials like superconductors and optical fibers.
• Agriculture – Fertilizers and pesticides.Production of fertilizers (Urea, Calcium Phosphate), insecticides, and pesticides to improve crop yield.
• Environment – Ozone layer protection.Understanding the causes of Ozone depletion and developing substitutes for CFCs (Chlorofluorocarbons).

2. Matter

Matter is anything that has mass and occupies space.Matter is classified into two broad categories based on its chemical composition.

• Pure substances
• Mixtures

Pure Substances :- Pure substances have a fixed composition. Their constituent particles cannot be separated by simple physical methods.

• Elements –Consist of only one type of atom. They can be monoatomic (He, Ne), diatomic (H₂, O₂)
• Compounds – Formed when atoms of different elements combine in a fixed ratio by mass. The properties of a compound are entirely different from its constituent elements. (H₂O, CO₂)

Mixtures :- Mixtures contain two or more substances in any ratio.

• Homogeneous mixture –The components completely mix with each other and its composition is uniform throughout. Examples: Air, Sugar solution, Alloys Uniform composition (air)
• Heterogeneous mixture –The composition is not uniform throughout and sometimes different phases are visible. Examples: Mixture of salt and sugar, grains and pulses with some dirt, smoke. Non uniform composition

3. Density

Density = Mass / Volume

4. Scientific Notation

Example 0.000025 = 2.5 × 10⁻⁵

5. Laws of Chemical Combination :- These laws form the basis of stoichiometry in chemistry.

• Law of conservation of mass(Antoine Lavoisier, 1789) :- Mass is neither created nor destroyed during a chemical reaction." The total mass of reactants must equal the total mass of products.
• Law of definite proportions(Joseph Proust, 1799) "A given compound always contains exactly the same proportion of elements by weight." Whether water is obtained from a tap, a river, or synthesized in a lab, the ratio of H:O is always 1:8 by mass.
• Law of multiple proportions:- If two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in a ratio of small whole numbers.
• Gay Lussac law:- When gases combine or are produced in a chemical reaction, they do so in a simple ratio by volume, provided all gases are at the same temperature and pressure.
• Avogadro law:- Equal volumes of all gases at the same temperature and pressure should contain an equal number of molecules." This law distinguished between atoms and molecules.

6. Mole Concept

1 mole = 6.022 × 10²³ particles

Example Molar mass of O₂ = 32 g/mol

7. Stoichiometry

Steps

• Write balanced equation
• Convert mass → moles
• Use mole ratio
• Find required quantity

Solved Example

Question Calculate molarity of 5 g NaOH in 450 mL solution Solution Molar mass = 40 g/mol Moles = 5 / 40 = 0.125 Volume = 0.450 L Molarity = 0.125 / 0.450 = 0.278 M

Exam Checklist

☑ Laws of chemical combination
☑ Mole concept
☑ Empirical formula
☑ Limiting reagent
☑ Molarity vs Molality