Ch-1 Chemistry Class 11 Short Notes - Some basic concepts of chemistry
1. Overview
Chapter 1 of Class 11 Chemistry, “Some Basic Concepts of Chemistry,” helps students understand the basic terms, laws, and calculations used throughout the subject.
These Class 11 Chemistry Chapter 1 Notes make concepts easy to revise for school exams, NEET, and JEE.
2. Importance of Chemistry
- Chemistry studies matter, its composition, and changes.
- It connects to biology, physics, and environmental science.
- Used in medicine, agriculture, and technology.
3. Laws of Chemical Combination
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Law of Conservation of Mass: Mass is neither created nor destroyed.
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Law of Definite Proportion: Elements combine in fixed ratios by mass.
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Law of Multiple Proportions: When elements form multiple compounds, mass ratios are simple whole numbers.
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Law of Gaseous Volumes (Gay-Lussac’s Law): Gases react in simple volume ratios.
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Avogadro’s Law: Equal volumes of gases contain equal numbers of molecules.
4. Dalton’s Atomic Theory
- All matter is made of atoms.
- Atoms of one element are identical.
- Compounds form when atoms combine in fixed ratios.
5. Atomic and Molecular Mass
- Atomic mass: Average mass of atoms of an element.
- Molecular mass: Sum of atomic masses in a molecule.
6. Mole Concept
- 1 mole = 6.022 × 10²³ particles (Avogadro’s number).
- Moles (n) = Given mass / Molar mass
- Helps in relating mass, volume, and number of atoms or molecules.
7. Molar Mass and Percentage Composition
- Molar Mass: Mass of 1 mole of a substance (in g/mol).
- % Composition = (Mass of element / Molar mass of compound) × 100
8. Empirical and Molecular Formula
- Empirical formula: Simplest ratio of atoms.
- Molecular formula: Actual number of atoms of each element.
9. Stoichiometry and Limiting Reagent
- Stoichiometry: Study of quantitative relationships in reactions.
- Limiting reagent: Reactant that gets completely used first, deciding how much product forms.
10. Chemical Equations
- Represent reactions symbolically.
- Must be balanced to obey the law of conservation of mass.
💡 Quick Summary
| Concept | Key Point |
|---|---|
| Atomic Mass | Mass of one atom relative to 1/12 of carbon-12 |
| Mole Concept | Links mass and number of particles |
| Laws of Combination | Explain how elements react |
| Stoichiometry | Predicts quantities in reactions |
| Limiting Reagent | Controls product amount |
📘 FAQs
Q1. What is the main topic of Chapter 1 in Class 11 Chemistry?
A: The chapter is titled “Some Basic Concepts of Chemistry” and introduces the mole concept, atomic mass, and laws of chemical combination.
Q2. Why is the mole concept important?
A: It helps relate the microscopic world of atoms to measurable quantities like grams and liters.
Q3. What are the main laws of chemical combination?
A: The five main laws are Conservation of Mass, Definite Proportions, Multiple Proportions, Gaseous Volumes, and Avogadro’s Law.
Q4. What is the difference between empirical and molecular formulas?
A: Empirical shows the simplest ratio; molecular shows the actual number of atoms.
Q5. Are these Class 11 Chemistry Chapter 1 Notes useful for NEET or JEE?
A: Yes, these notes cover all basic formulas and concepts frequently asked in competitive exams.
Q6. What is a limiting reagent?
A: It’s the reactant that determines how much product is formed during a chemical reaction.
Q7. How to calculate the number of moles?
A: Use the formula —
👉 Number of moles = Given mass / Molar mass.
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