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# Solutions 3. Atoms and Molecules - Chapter Review | Class 9 Science - Toppers Study

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## Solutions 3. Atoms and Molecules - Chapter Review | Class 9 Science - Toppers Study

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### You can Find Science solution Class 9 Chapter 3. Atoms and Molecules

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• NCERT Solutions And Textual questions Answers Class 9 Science
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Chapter 3 Science class 9

### Chapter Review class 9 Science Chapter 3. Atoms and Molecules

• Solutions 3. Atoms And Molecules - Chapter Review | Class 9 Science - Toppers Study
• Class 9 Ncert Solutions
• Solution Chapter 3. Atoms And Molecules Class 9
• Solutions Class 9
• Chapter 3. Atoms And Molecules Chapter Review Class 9

## Solutions 3. Atoms and Molecules - Chapter Review | Class 9 Science - Toppers Study

### Chapter Review:

• The smallest tiny particles of matter which cann't be divided further is called atom (Parmanu).
• The law of conservation of mass and the law of constant proportions these two laws of chemical combination were established by Lavoisier and Joseph L. Proust.
• Law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction.
• The law of constant proportions which is also known as the law of definite proportions.
• In a chemical substance the elements are always present in definite proportions by mass, this law is called the law of constant proportions.
• Dalton's theory was based on the laws of chemical combination.
• According to Dalton’s atomic theory, all matter, whether an element, a compound or a mixture is composed of small particles called atoms.
• Dalton's second postulate states "Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction".
• Dalton's third postulate states "atoms of a given element are identical in mass and chemical properties".
• Dalton's third postulate states "atoms of different elements have different masses and chemical properties".
• Atomic radius is measured in nanometres.
• IUPAC (International Union of Pure and Applied Chemistry) approves names of elements.
• The first letter of a symbol is always written as a capital letter (uppercase) and the second letter as a small letter (lowercase).
• Each element has a name and a unique chemical symbol.
• The atomic mass unit is writen as ‘u’ – unified mass.
• Carbon-12 isotope was chosen as the standard reference for measuring atomic masses.
• One atomic mass unit is a mass unit equal to exactly onetwelfth
(1/12th) the mass of one atom of carbon-12.
• Atoms form molecules and ions.
• These molecules or ions aggregate in large numbers to form the matter that we can see, feel or touch.
• A molecule can be defined as the smallest particle of an element or a
compound that is capable of an independent existence and shows all the properties of that substance.
• Atoms of the same element or of different elements can join together to form molecules.
• A molecule of oxygen consists of two atoms of oxygen and hence it
is known as a diatomic molecule, O2.
• 3 atoms of oxygen unite into a molecule these form ozone e.i O3.
• The number of atoms constituting a molecule is known as its atomicity.
• Atoms of different elements join together in definite proportions to form molecules of compounds.
• The charged atoms are known as ions.
• An ion is a charged particle and can be negatively or positively
charged.
• A negatively charged ion is called an ‘anion’ and the positively charged ion, a ‘cation’.
• Ions may consist of a single charged atom or a group of atoms that have a net charge on them.
• A group of atoms carrying a charge is known as a polyatomic ion.
• The chemical formula of a compound is a symbolic representation of its composition.
• The combining power (or capacity) of an element is known as its valency, in other hand the number of valnce electron is known as valancy of an atom.
• The quantity of a substance can be characterised by its mass or the number of molecules.
• One mole of any species (atoms, molecules, ions or particles) is that quantity in number having a mass equal to its atomic or molecular mass in grams.
• The number of particles (atoms, molecules or ions) present in 1 mole of any substance is fixed, with a value of 6.022 × 1023 ,  This number is called the Avogadro Constant or Avogadro Number.
• The mass of 1 mole of a substance is equal to its relative atomic or molecular mass in grams.
• Mass of 1 mole of a substance is called its molar mass.
• The mole is the amount of substance that contains the same number of particles (atoms/ ions/ molecules/ formula units etc.) as there are atoms in exactly 12 g of carbon-12.

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## Study Materials List:

##### Solutions ⇒ Class 9th ⇒ Science
1. Matter in Our Surroundings
2. Is Matter around us Pure
3. Atoms and Molecules
4. Structure of The Atom
5. The Fundamental Unit of Life
6. Tissues
7. Diversity in Living Organisms
8. Motion
9. Force and Laws of Motion
10. Gravitation
11. Work and Energy
12. Sound
13. Why Do We Fall ill
14. Natural Resources
15. Improvement in Food Resources

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