Summary of A B C For NEET 2026 CLASS | LALIT CHAUHAN SIR | CHEMISTRY CLASS - 02

Summary of "A B C For NEET 2026 CLASS | Lalit Chauhan SIR | Chemistry Class - 02"

This Chemistry Class, led by Lalit Chauhan Sir, focuses on fundamental concepts essential for NEET 2026 preparation, particularly related to atomic and molecular masses, the Mole Concept, and units of measurement in chemistry. The session emphasizes conceptual clarity, problem-solving, and the importance of focus during exams.

Main Ideas and Concepts

1. Micro World vs. Macro World

Micro world: Atoms, molecules, electrons, protons, neutrons (cannot be seen or measured directly).
Macro world: The visible, measurable world where we handle quantities like grams.
The mole acts as a "switch" to convert between micro and macro worlds.

2. Chemical Reactions and Electron Transfer

Chemical reactions involve transfer of electrons only.
Nucleus remains intact during chemical reactions; atoms cannot be divided (no half atoms).

3. Minimum Possible Quantity of an Element

Minimum sulfur: One atom or 32 amu (atomic mass units), but not fractions of atoms.
Minimum oxygen molecule (O₂): 32 amu (since O₂ has two atoms).
Minimum helium: One atom or 4 amu.
Emphasis on careful reading of questions to distinguish between atoms and molecules.

4. Atomic Number (Z) and Mass Number (A)

Atomic number (Z): Number of protons.
Mass number (A): Number of protons + neutrons.
Atomic weight depends on mass number.

5. Atomic Mass Unit (amu) and Avogadro’s Number (NA)

1 amu ≈ 1.66 × 10⁻²⁴ grams.
Avogadro’s Number (NA) ≈ 6.022 × 10²³ entities/mole.
Multiplying atomic mass in amu by NA converts microscopic mass to macroscopic mass in grams.
amu and NA are reciprocal units designed to maintain consistency between micro and macro worlds.

6. Relationship Between Atomic Mass, Mole, and Gram Atomic Weight

Atomic weight (in amu) × NA = gram atomic weight (in grams).
Example: Hydrogen atom = 1 amu; 1 mole of hydrogen atoms = 1 g.
This applies similarly to helium, carbon, nitrogen, oxygen, etc.
The concept extends to molecules (e.g., H₂ = 2 amu, 1 mole = 2 g, called gram molecular weight).

7. Units and Terminology

Gram atomic weight: Weight of one mole of atoms in grams.
Gram molecular weight: Weight of one mole of molecules in grams.
Actual weight: Weight of a single atom or molecule expressed in grams (very small, e.g., 1 atom of carbon ≈ 1.92 × 10⁻²³ g).
Proper chemical terminology:
- 1 mole of atoms = 1 g atom (not "g of atom").
- 1 mole of molecules = 1 g molecule.
- 1 mole of ions = 1 g ion.
Importance of correct reading and usage of these terms in exams.

8. Effect of Changing the Atomic Mass Unit (amu)

Hypothetical changes to amu are balanced by reciprocal changes in NA.
Weight of 1 mole of an element remains constant regardless of unit changes.
Example calculations with new units (U dash) show how weights adjust but mole weights remain consistent.

9. Exam Strategy and Conceptual Clarity

Importance of reading questions carefully and focusing on details (atom vs molecule, units).
Many students lose marks due to lack of focus and misunderstanding basic concepts.
Revision and practice are critical for mastering fundamentals.
No question is silly; asking questions and clearing doubts is encouraged.
The class encourages early joining and consistent practice for better preparation.

Methodology / Instructions (Bullet Points)

Understand the distinction between micro and macro worlds.
Use the Mole Concept as a conversion factor between amu and grams.
Always check whether the question refers to atoms or molecules.
Remember:
- Atomic number (Z) = number of protons.
- Mass number (A) = protons + neutrons.
Convert atomic/molecular mass from amu to grams using 1 amu = 1.66 × 10⁻²⁴ g.
Multiply atomic/molecular mass by Avogadro’s Number (6.022 × 10²³) to get gram atomic/molecular weight.
Use correct chemical terminology: "g atom," "g molecule," "g ion" (not "g of atom").
Practice solving questions involving:
- Minimum possible quantities of elements.