Toppers Study Toppers Study Toppers StudyGet CBSE Notes for Class 9 Science – 3. Atoms and Molecules: Laws of Chemical Combination. Clear, exam-focused notes with key concepts, formulas & solved examples.
CBSE Notes for Class 9 Science chapter 3. Atoms and Molecules: Laws of Chemical Combination, quick revision notes for Class 9 Science chapter 3. Atoms and Molecules Laws of Chemical Combination, Chapter-wise CBSE Revision Notes, CBSE Notes PDF Free Download, CBSE One Liner Notes Class 9, Half Yearly Revision Notes, CBSE Revision Notes Class 9 Science
Get CBSE Notes for Class 9 Science Chapter 3. Atoms and Molecules: Laws of Chemical Combination prepared by experts as per the latest NCERT syllabus and CBSE exam pattern. These concise and easy-to-understand notes cover important definitions, formulas, diagrams, and key concepts from the chapter to help students in quick revision and effective exam preparation. Whether you are studying for school tests, board exams, or competitive exams, these notes provide a reliable study resource. Designed in simple language with point-wise explanations, they save time and enhance learning efficiency. Download free PDF notes, explore solved examples, and strengthen your understanding of [Topic Name] for scoring high marks. Perfect for Class 9 students who want clear, structured, and exam-oriented notes for CBSE Science.
Element: The basic substance of matter that can not be simplified is an element.
Example: Hydrogen, Carbon, Oxygen, Iron, Silver and Gold etc.
Atom: The smallest tiny particles of matter which cann't be divided further is called atom (Parmanu).
Molecules: A group of two or more than two atoms of the same element or different elements that chemically bonded together is called molecules.
Example: O2, H2, N2, H2O, CO2, MgCl2 etc.
Compound: A molecule that contains more than one element is compound.
Example: H2O, CO2, NH3, BrCl2, CH4 etc.
The smallest tiny particles of element is atom. like atom of Hydrogen (H), atom of oxygen (O), atom of Carbon (C), atom of Magnesium (Mg) etc.
So all matters are made by these tiny particles of elements i.e atoms.
Formation of Matter
Atoms of elements
⇓
Molecules Or atoms
⇓
Compounds
⇓
Matters
Laws of Chemical Combination:
The laws of chemical combination were established by Lavoisier and
Joseph L. Proust.
The laws of chemical combination are two;
1. Law of conservation of mass: Law of conservation of mass states that
mass can neither be created nor destroyed in a chemical reaction.
2. Law of constant proportions: In a chemical substance the elements are
always present in definite proportions by mass.
Dalton's Atomic Theory:
British chemist John Dalton provided the basic theory about the nature of matter.
Dalton picked up the idea of divisibility of matter, which was till then just a philosophy. He took the name ‘atoms’ as given by the Greeks and said that the smallest particles of matter are atoms. His theory was based on the laws of chemical combination.
The postulates of dalton's theory:
(i) All matter is made of very tiny particles called atoms.
(ii) Atoms are indivisible particles, which cannot be created or destroyed in a
chemical reaction.
(iii) Atoms of a given element are identical in mass and chemical properties.
(iv) Atoms of different elements have different masses and chemical properties.
(v) Atoms combine in the ratio of small whole numbers to form compounds.
(vi) The relative number and kinds of atoms are constant in a given compound.
The name of elements and its symbol:
IUPAC (International Union of Pure and Applied Chemistry) approves names
of elements. Many of the symbols are the first one or two letters of the element’s name in English. The first letter of a symbol is always written as a capital letter (uppercase) and the second letter as a small letter (lowercase).
Example:
Hydrogen: H
Carbon : C
Aluminium: Al
Magnesium: Mg
Symbols of some elements are formed from the first letter of the name and a letter, appearing later in the name. Examples are:
(i) chlorine, Cl,
(ii) zinc, Zn etc.
Each element has a name and a unique chemical symbol.
Some examples of elements and their symbol.
Atomic Mass: An atomic mass unit or amu is one twelfth of the mass of an unbound atom of carbon -12 isotope. This is approximetely 1.67377 x 10 -27 kilogram (kg).
The relative atomic mass of the atom of an element is defined as the average mass of the atom, as compared to 1/12th the mass of one carbon-12 atom.
Atomic mass unit is abbreviated as 'amu' but on IUPAC latest recommendation, it is writen as 'u'.
Existance of atoms:
Atoms never exist independly. They form molecules or ions.
We can say, atoms exist in group.
For students preparing for board exams or competitive assessments, CBSE notes have become an indispensable tool. These notes summarize the NCERT textbooks, highlighting key concepts, formulas, definitions, and diagrams in a concise and easy-to-understand format. Unlike lengthy textbooks, CBSE notes allow students to focus on the most important points, saving valuable time during revision.
In conclusion, CBSE notes are not just a revision tool—they are a strategy. When used correctly, they help students cover the syllabus efficiently, improve retention, and approach exams with confidence. For exam-going students, the combination of structured notes, practice, and consistent revision is the key to achieving top results.
Ace your exams with CBSE Notes for Class 9 Science chapter 3. Atoms and Molecules: Laws of Chemical Combination. These notes provide a clear explanation of important concepts, formulas, diagrams, and solved examples from the NCERT syllabus. Specially designed for Class 9 students, the notes are structured in a simple, point-wise manner to make revision quick and effective. Whether you are preparing for school tests, board exams, or competitive exams, these Science notes will boost your confidence and save valuable study time. You can also download Science class 9 chapter 3. Atoms and Molecules free PDF notes for offline learning. With easy-to-grasp language, exam tips, and well-organized content, these CBSE Science notes on chapter 3. Atoms and Molecules – Laws of Chemical Combination are the perfect study companion for scoring high marks and mastering the subject.
CBSE class 10 Science notes are available completely free in PDF, and these all notes are quick revising materials that help you prepare for your upcoming board exams. Students can easily access CBSE notes pdf free download class 10 Science and get free CBSE notes class 10 Science notes designed strictly as per the latest NCERT syllabus. These Class 10 CBSE notes and Class 10 Science notes are short, simple, and to the point, making them perfect for last-minute revisions. You can also refer to NCERT book notes for class 10 that cover every chapter in an easy-to-understand manner. With these Quick revision notes Science class 10, you save time while covering all important formulas, definitions, and concepts.
Download worksheets and assignments for better practice and revision.