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# Xam Idea Class 9 Science Chapter 3 Solutions: Atoms And Molecules

Xam Idea Class 9  Science Solutions for Chapter 3 – Atoms and Molecules include exercise-wise solutions to all the questions for your better exam preparation. All these solutions are created by our best team of subject experts. These solutions not only follow the latest CBSE Class 9 Science syllabus but are in accordance with the latest exam pattern laid down by CBSE. We have also ensured to follow the NCERT textbooks while formulating the solutions to these Xam Idea Solutions.

Atoms and Molecules is a very interesting chapter which will help you in learning about concepts like cation, anion, molecules and molar mass. The development of concepts becomes much easier with the connection between the chapter and the examples that are based on reality and life around us. Our Xam Idea Class 9 Science Solutions for Chapter 3 – Atoms and Molecules consist of 6 exercises.

There are different categories of questions in each exercise as per the exam pattern of CBSE. These questions include very short answer type questions, short answer type questions, long answer type questions, higher-order thinking skills and value-based questions. These exercises cover all the essential sections of the chapter and help in a very easy and swift revision of them along with complete practice.

## Important Topics for Xam Idea Class 9  Science Solutions Chapter 3 – Atoms and Molecules

Law of Conservation of Mass

You will come across the law of conservation of Mass in this chapter. It contributes to the laws of chemical combination. This law states that mass can neither be created nor can it be destroyed in case of a chemical reaction.

Law of Constant Proportion

Just like the law of conservation of mass, this law also contributes to the laws of chemical combination. It states that in case of a chemical substance the elements are always present in definite proportions by mass.

Dalton’s atomic theory

This chapter will introduce you to Dalton’s Atomic Theory. Dalton’s atomic theory has four postulates –

• The first postulate states that all the forms of matter are made of very small particles which are known as atoms
• The second postulates state that atoms can not be created by any means nor is it possible to form them.
• For a single element, all its atoms will be identical to each other. Whereas in case of different elements their atoms will differ from each other.
• The atoms of any element combine together in the whole number ratio in order to produce a large number of atoms or a compound of a new substance.

Molecule

You will get to know that a molecule is a group of two or more atoms which are chemically bonded together. An attractive force acts between them in order to keep them bonded together. It is also defined as the smallest particle present in an element or a compound that is capable of independent existence and shows all the characteristics of that compound.

Atomicity

In this chapter, you will learn about atomicity. Atomicity is the term given to the number of atoms which are present in one molecule of a substance. In the course of solving chapter problems, you will find a lot of questions which are dependent on this concept.

Atomic Mass Unit

In this chapter, you will come across the concept of an atomic mass unit. Atomic mass unit is equal to one-twelfth of the mass of one Carbon – 12 atom.

Percentage Composition of Elements and Compounds

Percentage composition refers to the percentage amount of the mass of each element in the total composition of the compound. This concept is majorly used in the numerical problems of the chapter.

### Exercise Discussion of Xam Idea Class 9  Science Solutions Chapter 3 – Atoms and Molecules

• There are a total of ten questions in this exercise.
• The first question requires you to name two scientists who established the laws of chemical combination.
• The second question asks for an example of a triatomic molecule of an element.
• The third question requires you to define atomicity and the fourth question presents two molecules whose atomicity has to be determined.
• The fifth question asks to define ions along with examples and the sixth question talks about ions and cations
• Question 7 is an observation based question where you are required to analyse the atomic number of the elements and tell which of them will form a cation.

• There are a total of 11 questions in this exercise.
• The exercise begins with a very simple question where you are required to give an example in order to demonstrate the law of conservation of mass.
• The second question presents a bunch of symbols and elements and you are required to detect which of them are correct and which of them are wrong.
• The next question also belongs to the same category where you need to find which of the given molecules in the question are tri – atomic and which of them are tetra – atomic.
• Question four requires you to distinguish between the actual mass of molecules and the gram molecular mass.
• Question 5 is based on the concept of molecular mass where you need to find the molecular mass of sodium carbonate.
• Question six requires you to find how many moles are present in 4g of sodium hydroxide.
• In the eighth question, you need to find the mass of sulphur trioxide with the help of all the information given about Ammonia in the question.
• Question nine requires you to find the differences in the composition of carbon dioxide in the given two cases and state the law that is associated with it.
• Question 10 is also numerical which requires you to find the number of atoms present in a black dot marked on paper with the help of the information provided in the question.
• The last question discusses whether or not the solubility of a substance changes with the temperature.

• There are eleven questions in this exercise.
• The first question requires you to write the cations and the anions present in the compounds given in the question.
• The second question requires you to find the mass percentage of the compounds given in the question.
• The third question again has a bunch of compounds and requires you to classify them on the basis of their atomicity.
• Question four requires you to calculate the molecular mass of the compounds mentioned in the question.
• Question five is a theory based question and requires you to define ionic and molecular compounds along with examples.
• Question three needs you to give the significance of mole.
• Question seven is a numerical based problem where you need to find the number of atoms in 0.5 mol of water.
• Question eighth is also similar and requires you to find the number of moles for the compounds and elements given in the question.
• Question nine requires you to find the mass percentage of each element of sodium chloride in one molecule of it
• The tenth question is also a numerical based problem based on the fundamentals of a number of particles. The last question is also a numerical problem.

• There are 16 questions in this exercise

• All the questions included in this exercise are based on numerical problems.
• These revolve around the concepts of decreasing mass, mass percent, mole ratio, molecules of a substance and molecular mass.

HOTS (Higher Order Thinking Skills)

• The exercise has a total of five questions.

• The first question requires you to analyse the given table and assess whether the compound is pure or not.
• The second question is a formula based formula where you need to find the number of molecules present in the drop of water mentioned in the question.
• The third question inquires about the fraction of the mass of water due to neutrons.
• In the fourth question, you need to give ways for differentiating between salt and sugar without tasting it.

• The fifth question is also a numerical-based question where you need to find the number of electrons present is carbon tetrachloride.

### Why Use Xam Idea Class 9  Science Solutions Chapter 3 – Atoms and Molecules

• We have presented Xam Idea Class 9  Science Solutions for Chapter 3 – Atoms and Molecules in a stepwise fashion.
• Our experts have used simple language to ensure that you understand all the concepts of the chapter thoroughly.
• We have ensured that each and every question from the chapter has been entertained and resolved with expertise.
• We follow NCERT textbook for Class 9 Science along with the CBSE syllabus and exam pattern while formulating Xam Idea Class 9 Science Solutions.
• All our Xam Idea Class 9 Solutions are for FREE and are presented in an easy to access systematic manner.
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