Class 9 Exam > Class 9 Notes > Class 9 chapter 3 atoms and molecules notes
Class 9 chapter 3 atoms and molecules notes PDF Download
Class IX Science
Notes for Atoms and Molecules
Notes for Atoms and Molecules
Syllabus
Particle nature, Basic units, Atoms and molecules, Law of constant proportions, Atomic and molecular masses.
Facts that Matter
• Law of Chemical Combination
Given by Lavoisier and Joseph L. Proust as follows:
(i) Law of conservation of mass: Mass can neither be created nor destroyed in a chemical reaction.
e.g.,A B-C D
Reactants R Products
Mass of reactants = Mass of products
(ii) Law of constant proportion: In a chemical substance the elements are always present in definite proportions by mass.
E.g., in water, the ratio of the mass of hydrogen to the mass of oxygen is always 1 : 8 respectively.
These laws lacked explanation. Hence, John Dalton gave his theory about the matter. He said that the smallest particle of matter is called ‘atom’.
• Dalton’s Atomic Theory
1. Every matter is made up of very small or tiny particles called atoms.
2. Atoms are not divisible and cannot be created or destroyed in a chemical reaction.
3. All atoms of a given element it are same in size, “mass and chemical properties.
4. Atoms of different elements are different in size, mass and chemical properties.
5. Atoms combine in the ratio of small whole number to form compounds.
6. The relative number and kinds of atoms are constant in a given compound. 9
• Atom
Atoms are the smallest particles of an element which can take reaction.
Size of an atom: Atomic radius is measured in nanometres.
Atomic radii of hydrogen atom = 1 × 10–10m.
Symbols of atoms:
(a) Symbols for some elements as proposed by Dalton:
(b) Symbols of some common elements:
| Name of the element | Latin name | Symbol | |
| Hydrogen | � | H | |
| Helium | � | He | |
| Carobon | � | C | |
| Copper | Cuprum | Cu | |
| Cobalt | Co | ||
| Chlorine | Cl | ||
| Cadmium | Cd | ||
| Boron | B | ||
| Barium | Ba | ||
| Bromine | Br | ||
| Bismuth | Bi | ||
| Sodium | Natrium | Na | |
| Potassium | Kalium | K | |
| Iron | Ferrum | Fe | |
| Gold | Aurum | Au | |
| Silver | Argentum | Ag | |
| Mercury | Hydragyrum | Hg |
• Molecule
It is the smallest particle of an eleme4It- or a dolnpound which can wxist independently.
• Molecules of an element constitutes same type of atoms. 1.w
• Molecules may be monoatomic, di-atomic or polyatomic. IT .
• Molecules of compounds join together in defmite proportionsrand constitutes different type of atoms.
• Atomicity
The number of atoms constituting a Molecule is known as its atomicity.
| Name of the element | Atomicity | Molecules formula | |
| Helium | Monoatomic | He | |
| Neon | Monoatomic | Ne | |
| Argon | Monoatomic | Ar | |
| Sodium | Monoatomic | Na | |
| Iron | Monoatomic | Fe | |
| Aluminium | Monoatomic | Al | |
| Hydrogen | Di-atomic | H2 | |
| Oxygen | Di-atomic | O2 | |
| Chlorine | Di-atomic | Cl2 | |
| Nitrogen | Di-atomic | N2 | |
| Phosphorus | Polyatomic (Tetra) | P4 | |
| Sulphur | Polyatomic (Octa) | S8 |
• Ions
The charged particles (atoms) are called ions, they charge or negative charge on it:
Negatively charged ionis called anion (C1�).
Positively charge ion is called cation (Na ).
• Valency
The combining capacity of an element is known as its valency: Valency is used to fmd out how atom of an element will combine with the atom of another element to form a chemical compound.
(Every atom want, to become stable, to do so it may loose, gain or share electrongs.
(i) If an atom consists of 1, 2 or 3 electrons in its valgncesI ell then its valency is 1, 2 or 3 respectively,
(ii) If an atom consists of 5, 6 or 7 electrons in the outermost shell, then it will gain 3, 2 or 1 electron respectively and its valency will be 3, 2 or 1 respectively.
(ii) If an atom has 4 electrons in the outermost shell than it will she this electron and hence its valency will be 4.
(iv) If an atom has 8 electrons in the outermost shell then its valency is 0.• Chemical Formulae
Rules: (i) The valencies or charges on the ion must balance.
(ii) A metal and non-metal compound should show the name or symbols of the metal first.
e.g., Na Cl– → NaCl
(iii) If a compound consist of polyatomic ions. The ion before writing the number to indicate the ratio.
e.g., [SO4]2– → polyatomic radical
H1 SO42– → H2SO4.
Chemical formula of some simple compounds
(a) Calcium hydroxid
(b) Aluminium oxide
• Molecular Mass
It is the sum of the atomic masses of all the atoms in a molecule of the substance. It is expressed in atomic mass unit (u).
e.g., 2H O2 H2O [H = 1, 0 = 16]
1 × 2 16 = 18 u
• Formula Unit Mass
It is the sum of the atomic masses of all atoms in a formula unit of a compound. The constituent particles are ions.
e.g., Na Cl– → NaCl
1 × 23 1 × 35.5 = 58.5 u
• Mole Concept
Definition of mole: It is defined as one mole of any species (atom, molecules, ions or particles) is that quantity in number having a mass equal to its atomic or molecular mass in grams.
1 mole = 6.022 × 1023 in number
Molar mass = mass of 1 mole → is is always expressed in r gram, and is also known as gram atomic mass.
1u of hydrogen has → 1 atom of hydrogen
lg of hydrogen has → 1 mole of hydrogen
= 6.022 × 1023 atoms of hydrogens
FAQs on Class 9 chapter 3 atoms and molecules notes
| 1. What are atoms and molecules? |  |
Ans. Atoms are the basic building blocks of matter, consisting of a nucleus (containing protons and neutrons) surrounded by electrons. Molecules, on the other hand, are formed when two or more atoms chemically combine together.
| 2. How do atoms and molecules differ from each other? | |
Ans. Atoms are individual particles that cannot exist independently, while molecules are formed when atoms chemically bond together. Molecules have specific properties and can exist independently.
| 3. Can atoms be broken down into smaller particles? | |
Ans. Yes, atoms can be further broken down into smaller particles called subatomic particles. These include protons, neutrons, and electrons, which are the fundamental constituents of atoms.
| 4. What is the role of atoms and molecules in chemical reactions? | |
Ans. Atoms and molecules play a crucial role in chemical reactions. During a chemical reaction, atoms rearrange their bonds to form new molecules with different properties. This rearrangement is responsible for the formation of new substances.
| 5. Why is the study of atoms and molecules important? | |
Ans. The study of atoms and molecules is important because it helps us understand the fundamental nature of matter and its behavior. It forms the basis of various scientific disciplines such as chemistry and physics, enabling advancements in fields like medicine, materials science, and environmental studies.
Related Exams
About this Document
|
4.73/5 Rating |
|
Nov 16, 2024 Last updated |
Document Description: Class 9 chapter 3 atoms and molecules notes for Class 9 2024 is part of Class 9 preparation. The notes and questions for Class 9 chapter 3 atoms and molecules notes have been prepared according to the Class 9 exam syllabus. Information about Class 9 chapter 3 atoms and molecules notes covers topics like and Class 9 chapter 3 atoms and molecules notes Example, for Class 9 2024 Exam. Find important definitions, questions, notes, meanings, examples, exercises and tests below for Class 9 chapter 3 atoms and molecules notes.
Introduction of Class 9 chapter 3 atoms and molecules notes in English is available as part of
our Class 9 preparation & Class 9 chapter 3 atoms and molecules notes in Hindi for Class 9
courses. Download more important topics, notes, lectures and mock test series for Class 9
Exam by signing up for free. Class 9: Class 9 chapter 3 atoms and molecules notes
Description
Full syllabus notes, lecture & questions for Class 9 chapter 3 atoms and molecules notes - Class 9 | Plus excerises question with solution to help you revise complete syllabus | Best notes, free PDF download
Information about Class 9 chapter 3 atoms and molecules notes
In this doc you can find the meaning of Class 9 chapter 3 atoms and molecules notes defined & explained in the simplest way possible.
Besides explaining types of Class 9 chapter 3 atoms and molecules notes theory,
EduRev gives you an ample number of questions to practice Class 9 chapter 3 atoms and molecules notes tests, examples and also practice Class 9 tests.
Download as PDF
|
Explore Courses for Class 9 exam
|
|
Signup for Free!
Signup to see your scores go up within 7 days! Learn & Practice with 1000+ FREE Notes, Videos & Tests.
Related Searches
Important questions
,Objective type Questions
,Extra Questions
,shortcuts and tricks
,Viva Questions
,Class 9 chapter 3 atoms and molecules notes
,study material
,Summary
,MCQs
,Sample Paper
,video lectures
,ppt
,Free
,past year papers
,Class 9 chapter 3 atoms and molecules notes
,Previous Year Questions with Solutions
,Exam
,practice quizzes
,Semester Notes
,mock tests for examination
,Class 9 chapter 3 atoms and molecules notes
;
Additional Information about Class 9 chapter 3 atoms and molecules notes for Class 9 Preparation
Class 9 chapter 3 atoms and molecules notes Free PDF Download
The Class 9 chapter 3 atoms and molecules notes is an invaluable resource that delves deep into the core of the Class 9 exam.
These study notes are curated by experts and cover all the essential topics and concepts, making your preparation more efficient and effective.
With the help of these notes, you can grasp complex subjects quickly, revise important points easily,
and reinforce your understanding of key concepts. The study notes are presented in a concise and easy-to-understand manner,
allowing you to optimize your learning process. Whether you're looking for best-recommended books, sample papers, study material,
or toppers' notes, this PDF has got you covered. Download the Class 9 chapter 3 atoms and molecules notes now and kickstart your journey towards success in the Class 9 exam.
Importance of Class 9 chapter 3 atoms and molecules notes
The importance of Class 9 chapter 3 atoms and molecules notes cannot be overstated, especially for Class 9 aspirants.
This document holds the key to success in the Class 9 exam.
It offers a detailed understanding of the concept, providing invaluable insights into the topic.
By knowing the concepts well in advance, students can plan their preparation effectively.
Utilize this indispensable guide for a well-rounded preparation and achieve your desired results.
Class 9 chapter 3 atoms and molecules notes
Class 9 chapter 3 atoms and molecules notes Notes offer in-depth insights into the specific topic to help you master it with ease.
This comprehensive document covers all aspects related to Class 9 chapter 3 atoms and molecules notes.
It includes detailed information about the exam syllabus, recommended books, and study materials for a well-rounded preparation.
Practice papers and question papers enable you to assess your progress effectively.
Additionally, the paper analysis provides valuable tips for tackling the exam strategically.
Access to Toppers' notes gives you an edge in understanding complex concepts.
Whether you're a beginner or aiming for advanced proficiency, Class 9 chapter 3 atoms and molecules notes Notes on EduRev are your ultimate resource for success.
Class 9 chapter 3 atoms and molecules notes Class 9 Questions
The "Class 9 chapter 3 atoms and molecules notes Class 9 Questions" guide is a valuable resource for all aspiring students preparing for the
Class 9 exam. It focuses on providing a wide range of practice questions to help students gauge
their understanding of the exam topics. These questions cover the entire syllabus, ensuring comprehensive preparation.
The guide includes previous years' question papers for students to familiarize themselves with the exam's format and difficulty level.
Additionally, it offers subject-specific question banks, allowing students to focus on weak areas and improve their performance.
Study Class 9 chapter 3 atoms and molecules notes on the App
Students of Class 9 can study Class 9 chapter 3 atoms and molecules notes alongwith tests & analysis from the EduRev app,
which will help them while preparing for their exam. Apart from the Class 9 chapter 3 atoms and molecules notes,
students can also utilize the EduRev App for other study materials such as previous year question papers, syllabus, important questions, etc.
The EduRev App will make your learning easier as you can access it from anywhere you want.
The content of Class 9 chapter 3 atoms and molecules notes is prepared as per the latest Class 9 syllabus.
|
© EduRev
|
Education Revolution
|
Follow Us
|
Signup to see your scores
go up within 7 days!
Access 1000+ FREE Docs, Videos and Tests
Takes less than 10 seconds to signup