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CBSE NOTES Class 9 Science Chapter-3. Atoms and Molecules Ions And Atoms

Get CBSE Notes for Class 9 Science – 3. Atoms and Molecules: Ions And Atoms. Clear, exam-focused notes with key concepts, formulas & solved examples.

CBSE Notes for Class 9 Science chapter 3. Atoms and Molecules: Ions And Atoms, quick revision notes for Class 9 Science chapter 3. Atoms and Molecules Ions And Atoms, 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

CBSE NOTES Class 9 Science Chapter-3. Atoms and Molecules Ions And Atoms

CBSE Notes for Class 9 Science – chapter 3. Atoms and Molecules: Ions And Atoms | Free PDF & Exam-Focused Study Material

Get CBSE Notes for Class 9 Science Chapter 3. Atoms and Molecules: Ions And Atoms 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.

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    CBSE Notes ⇒ Class 9th ⇒ Science

    3. Atoms and Molecules

    Ions And Atoms

    3. Atoms and Molecules

    Ions: The charged atoms are known as ions. 

    Ions have two types of charge.

    (1) Anion : A negatively charged ion is called an ‘anion’.

       Eg: Cl-, O-2, S2-, N3-, Br-, H- etc. 

    These all atoms have negative charged so they are ions with anoin. 

    Note: All non-metals form anoin. 

    (2) Cation : The positively charged ion is called a ‘cation’.

       Eg. Na+, K+, Ag+, Cu+, Mg2+, Ca2+, Zn2+, Fe2+, Al3+ etc. 

    These all atoms have positive charged so they are ions with cation.  

    Note: All metals form cation.

    For example, sodium chloride (NaCl). Its constituent particles are positively
    charged sodium ions (Na+) and negatively charged chloride ions (Cl–). Ions may consist of a single charged atom or a group of atoms that have a net charge on them.

    Polyatomic ion: A group of atoms carrying a charge is known as a polyatomic ion.

    Valency: The combining power (or capacity) of an element is known as its valency.

    Writing Chemical Formulae

    The chemical formula of a compound is a symbolic representation of its composition.

    First many questions might have risen in the mind.

    (i) How are atoms charged? 

    (ii) How different aions have different charges like -, 2-, 3- or +, 2+, and 3+ etc ?

    (iii) What is combining power or capacity of an element ? 

    (iv) In waht manner compounds form? 

     

    For understanding this ion and its type anion and cation as well as valancy we need to learn more about the structure of atom before learning writing chemical formula.

    Structure of atom:

                                             

    Always rememer some points these are as follow:

    • An atom has three non-atomic particles i.e electrons, protons and neutrons.
    • All electrons moves around the nucleus of an atom in different shells. 
    • Protons and neutrons are present in nucleus of an atom. 
    • All electrons have same negative charge and no mass. 
    • All protons have same positive charge and mass as 1 unit. 
    • Neutrons have no charge but have mass as 1 unit.
    • The numbers of electrons and protons are equal in an atom.
    • The numbers of neutrons may be greater, equal or less than protons. 
    • The number of protons present in nucleus of an atom is also calculated as atomic number of the same atom. 
    • The sum of protons and neutrons present in nucleus of an atom is calculated as atomic mass of the same atom. 
    • Hydrogen has no any neutron in its nucleus. There is only 1 proton.
    • Each orbit is also known as shell and they are called energy levels.
    • These orbits or shells are represented by the letters K,L,M,N,… or the numbers, n=1,2,3,4,….

    Distribution of electrons in different shells or orbits.

    The maximum number of electrons present in a shell is given by the formula 2n2, where ‘n’ is the orbit number or energy level index, 1,2,3,….

    For example:

    It means the first shell can have only maximum 2 electrons, second can have maximum 8 electrons, third shell can have maximum 18 electrons and forth shell can have maximum 32 electrons. 

    See the table:

    Electronic Configuration And Valency Table 
    Atomic No. Symbol (Atom) No. of electrons  k shell  L shell  M shell  N shell  Valency

     1.

     2. 

     3. 

     4. 

     5. 

     6.

     7.

     8.

     9.

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     11.

     12. 

     13. 

     14.

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     16. 

     17.

     18. 

     19.

     20.

     H

     He

     Li

     Be

     B

     C

     N

     O

     F

     Ne

     Na 

     Mg 

     Al

     Si

     P

     S

     Cl

     Ar

     K 

     Ca

     1

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    Other Pages of this Chapter:

    Page 1 Laws of Chemical Combination

    Page 2 Ions And Atoms

    Page 3 Formation of Simple Molecules

    Page 4 Molecular Mass

    Page 5 Assignment

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