Class 9 Science Chapter 3-Atoms & Molecules

Class 9 Science Chapter 3 Notes 

Go through our helpful Chemistry Chapter 3 Atoms And Molecules Class 9th notes and other subject-wise material for revision. Our meticulously prepared notes are here to help students understand the basic concepts of atoms and molecules, which are important for exams. Curated by our experts at Educart, these notes are as per the latest CBSE syllabus and exam pattern. They're presented in a simple, concise, pointwise format, making it easier for you to grasp and memorize key concepts quickly. With our online revision notes, you can breeze through the entire chapter notes of “Atoms And Molecules” in just 20-25 minutes or less!

CBSE Class IX Science Chapter 3 DoE Worksheet

Students can attempt the class 9 NCERT “Atoms And Molecules” Chapter 3 worksheet that contains questions, exercises, and activities designed to help students engage with the concepts taught in this chapter. This DoE worksheet covers experiments, problem-solving tasks, and theoretical questions related to the design of experiments.

Download the PDFs of DoE Worksheets for class 9 chapter 3 - Atoms And Molecules notes to become more engaged in this chapter. 

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CBSE Class 9 Atoms And Molecules Experiential Activities

To download the Experiential Learning Activity of  Atom And Molecules Class 9 PDF click the link below 

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CBSE Class 9 Atoms And Molecules Important Questions

Now find class 9 science chapter 3 question answers in one place. This PDF contains all the important questions that have a high chance of being asked in the exams. Practice Atoms And Molecules Class 9 question and answer to learn your progress. Downloadable links to the free PDFs are available below.

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CBSE Class 9 Atoms And Molecules Question Bank

CBSE Class 9 Atoms And Molecules notes in the form of a question bank are available for download. Click on the link below, to download the detailed explanations of all the important questions in the form of PDFs.

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CBSE Class 9  Atoms And Molecules Support Material

Below, we have provided Class 9 Atoms And Molecules Notes for Support Materials that cover concept mapping along with an easy explanation of difficult concepts in a simplified way.

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Revision Notes Chapter 3: Atoms And Molecules

Understanding Atoms and Molecules

Atoms and molecules play an important role in chemical reactions. Atoms are tiny particles that make up matter and have the characteristics of the element they belong to. Some atoms don't stand alone; instead, they join together to form ions or molecules. When two or more atoms bond together through chemical bonds, they form molecules. 

The molecules are the smallest parts of an element that still show its properties. Sometimes, just one atom can form a molecule, while other times, it takes two or more atoms bonding together to form a molecule.

Laws of Chemical Combination

This law was first formulated by the French chemist Joseph Louis Proust in the late 18th century based on his experiments with chemical compounds. This law is further divided into two laws

1. Law of Conservation of Mass

This law states that in a closed system, mass is neither created nor destroyed in chemical reactions or physical changes. This means that the total mass of substances before a chemical reaction must equal the total mass of the substances after the reaction. In other words, the mass of the reactants is always equal to the mass of the products in a chemical reaction, even though the substances may change their form or arrangement.

2. Law of Fixed Proportion

The Law of Fixed Proportions, also known as the Law of Definite Proportions, states that a chemical compound always contains the same elements in the same proportions by mass, regardless of the source or how the compound is prepared. In other words, the ratio of the masses of the elements in a compound is constant.

For example, consider water (H2O). According to the Law of Fixed Proportions, regardless of whether the water is obtained from a natural source like a river or synthesized in a laboratory, it will always consist of two hydrogen atoms for every oxygen atom. This means that the ratio of hydrogen to oxygen in water is always 2:1 by mass.

Symbols of Some Elements

Aluminium (Al) 

Copper (Cu)

Nitrogen (N)

Argon (Ar)

 Fluorine (F)

 Oxygen (O)

Hydrogen (H)

 Silver (Ag)

Calcium (Ca) 

Iron (Fe) 

Sodium (Na)

Carbon (C) 

What is Atomic Mass?

Atomic mass, also known as atomic weight, refers to the average mass of an atom of a chemical element. It is expressed in atomic mass units (amu) or unified atomic mass units (u). The atomic mass of an element is determined by the number of protons and neutrons present in its nucleus. Since the mass of electrons is negligible compared to that of protons and neutrons, it is usually not considered when calculating atomic mass.

What is Molecular Mass?

Molecular mass is the sum of the atomic masses of all the atoms in a molecule. Molecular mass is expressed in atomic mass units (amu) or grams per mole (g/mol). 

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