Lakhmir Singh Chemistry Class 9 Solutions Chapter 3 - Atoms and Molecules

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Lakhmir Singh Chemistry Class 9 Solutions Chapter 3 - Atoms and Molecules

Lakhmir Singh Class 9 Chemistry Solutions Chapter 3 - Atoms and Molecules - Free PDF Download

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Summary of Chapter 3- Atoms and Molecules Class 9 Chemistry

Law of Chemical Combination

Atoms and molecules are functional and structural units of our world. Atoms and molecules define the physical and chemical properties of elements. This chapter covers the fundamentals of atoms and molecules.Chemical Reaction- this law defines products and reactants. The molecules that interact with one another to form a new compound are known as reactants, while the final compounds produced are known as products.

Law of Conservation of mass- this law states how mass can neither be created nor destroyed, it can just be converted from one form to another. The amount of energy present at a specific time in the Universe remains the same. This means the mass of reactants will be equal to the mass of products.
Law of constant proportions- this law states that the proportions of each element in a pure chemical compound remain the same no matter the amount of state of the compound.

Dalton’s Atomic Theory

This theory defines atoms as invisible particles that make up matter. The properties of all the atoms in a specific element are the same. The atoms of a specific element have the same chemical and physical properties but atoms of different elements have different chemical and physical properties. Different elements combine to form different molecules and different compounds. Atoms are invisible. Atoms cannot be created or destroyed. Any new compound is formed by the rearrangements of the existing elements.

Atomic Mass and Atomic Mass Unit

The atomic mass is equal to the summation of protons and neutrons present in an atom. The mass of a single atomic particle is known as atomic mass, it is expressed as a unified atomic mass unit(AMU) by international standards.

Molecular mass, Mole concept, and Avogadro Number

The molecular mass of a molecule is the summation of the masses of elements present in it. Mole Concept is the most standard way used to express the amount of each element, compound, or molecule used or present in a chemical reaction. Avogadro number is the number used to represent the number of molecules present in one mole. 6.022×1023 molecules are the Avogadro number.

FAQs on Lakhmir Singh Chemistry Class 9 Solutions Chapter 3 - Atoms and Molecules

1. Why should I solve Lakhmir Singh Class 9?

Lakhmir Singh is a reliable source to prepare for Class 9 CBSE. Lakhmir Singh is a teacher who has written many books to refer to while preparing for secondary and higher secondary. Solving publication books gives you the confidence to solve the exam paper. Makes you realize your silly mistakes. As a result, you can avoid making them again. Lakhmir Singh is famous for Physics, Chemistry, and Biology. To ace your exam you should try to solve Lakhmir Singh of all three sub-subjects of science.

2. Is the atomic mass of any element the same?

The atomic mass of each element is unique to itself. The atomic mass of each element is different as each element carries atoms with a different number of neutrons, electrons, and protons. The mass of electrons is not taken into account while calculating atomic mass as its mass is so small that it can be neglected. Thus, we can say the mass of every atom lies in the nucleus of an atom. Mole and molecular mass are other ways to measure the mass of an element or a molecule.

3. Why do different elements have different chemical properties?

Though the basic structure and function of each element are the same, the number of neutrons, electrons, and protons present in the atoms of each element are different. The most influential feature of an atom is the number of electrons present in its outermost orbit. The number of electrons present in the outermost orbit defines an element’s valency. Valency plays a very important role in deciding both the chemical properties and physical properties of an element. Having a different number of electrons leads to having different chemical properties.

4. How should I prepare for Chapter 3 Chemistry CBSE Class 9?

Have the basic concepts of the entire chapter clear. Make notes on the Dalton Atomic Theory and revise them every day. Know the clear difference between atomic mass, molecular mass, and moles clearly. Chemistry is simple but requires attention to detail to crack the MCQs asked. Know the atomic mass and the atomic number of the first 30 elements in the periodic table. You should know the entire statements of Law of Conversion of Mass and Law of Constant Proportions.

5. Does the Avogadro number change?

Avogadro number represents the number of molecules present in each mole of every element. This number doesn’t change for any elements or atoms. This number is the same for every element present in the periodic table. With the help of this number, you can find the atomic mass. Moles of any element present in a reaction can be known with the help of the Avogadro number. No matter what, the Avogadro number never changes and always is represented by a single number.

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