structure of atom class 9 assignment

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Structure of Atom Worksheet for Class 9 PDF with Answers

In Class 9 Science there is a chapter “Structure of Atom”, it is a crucial lesson for the students as they get to know all the basic topics of Structure of Atom. Since it is an important lesson, students should take Structure of Atom Worksheet Class 9 to better develop an understanding of the concepts explained.

It is very important for Class 9 students to practise questions of the chapter Structure of Atom because it will help them create their own exam strategy to score well in the upcoming final examination. 

In addition to that, Structure of Atom Worksheet Class 9 has quite interactive and creative tasks which boosts student’s creativity level.

Structure of Atom Worksheet With Solutions

The questions in the chapter Structure of Atom worksheet for Class 9 are provided with solutions. Through these solutions, students can easily solve all their doubts. By clearing the doubts of Structure of Atom, students can build a strong foundation. Accordingly students can also score good marks in questions related to the chapter Structure of Atom. The subject matter experts at Selfstudys has prepared Structure of Atom Worksheet With Solutions in a way that helps students answer all types of questions regardless of its difficulty.

Structure of Atom Worksheet Class 9 PDF

Class 9 students can easily download the Portable Document Format (PDF) of Structure of Atom worksheet with the help of Selfstudys website. This can help Class 9 students to understand all the topics and concepts of the chapter Structure of Atom which will help students increase their self-confidence level. A perfect level of self- confidence can easily decrease students' level of stress to prepare for the chapter Structure of Atom.

How to Download Structure of Atom Worksheet Class 9?

To look through the questions included in Structure of Atom worksheet Class 9, students can follow the given steps. These steps are the easiest one that one can follow to download Structure of Atom Worksheet Class 9. 

• Open the Selfstudys website. 
• Bring the arrow towards the CBSE which can be seen in the navigation bar. 
• A drop down menu will appear, select KVS NCERT CBSE Worksheet.

• A new page will appear, Class 9 from the list of classes.

• Click Science from the list of subjects.

• Again a new page will appear, now select Structure of Atom Worksheet from the list of chapters. 

Features of Structure of Atom Worksheet Class 9

Before solving questions from Structure of Atom worksheet Class 9, students should understand what makes Structure of Atom Worksheet Class 9 PDF special. Features of the worksheet are discussed below: 

• All Concepts are Covered: In Structure of Atom worksheet Class 9, all concepts and topics are covered in an elaborate manner in the questions format. Through this elaboration, students can understand all the topics of the chapter Earth in a better way.  
• Explained in an Easy Language: Answers of Structure of Atom Worksheet Class 9 is explained in an easy language which helps students easily understand the process of answering questions.  
• Varieties of Questions are Included: In the Class 9 Structure of Atom worksheet, varieties of questions are included. Through this students can solve all kinds of questions of the chapter Structure of Atom. 
• Eye Catching Format: Structure of Atom Worksheet of Class 9 is considered to be an eye catching one. This eye-catching format can attract many students to solve the questions of the chapter Structure of Atom.
• Solutions are Provided: For all the questions in the worksheet of Class 9 Structure of Atom, solutions are provided. Through the solutions, Class 9 students will be able to solve challenging questions which will help them develop a critical thinking capability.
• According to the Class 9 Syllabus: The questions in Class 9 Science Structure of Atom Worksheet are as per the Class 9 Syllabus and prescribed NCERT books. With the help of this, kids will be able to make their foundational understanding stronger.

How to Know If You're Ready for Structure of Atom Worksheet Class 9? 

First of all Class 9 students need to complete the chapter Structure of Atom from the main Science book. After covering all the topics, definitions and concepts from the chapter, students are totally ready to solve the questions from Structure of Atom Worksheet Class 9. Solving the questions from the Class 9 worksheet can help students to increase their conceptual understanding of Structure of Atom. 

What Is Structure of Atom Worksheet Class 9 and How to Use It?

Structure of Atom worksheet Class 9 is mainly given to students to practise a variety of questions. After practising questions from Structure of Atom worksheet, students can also look through the answers. Answers for all questions can help students to improve their practising skills. These skills can help Class 9 students to increase their level of understanding. 

Parents are advised to tell their Class 9rd kids to begin solving Structure of Atom Worksheet Class 9 the moment they finish their study of the chapter. Doing this, will help students brush up their all learning as well as be completed for upcoming annual exams or tests.

Advantages of Structure of Atom Worksheet Class 9

Solving questions from Structure of Atom worksheet Class 9, students can be benefited a lot. Those important advantages are: 

• Boosts Confidence Level: To solve questions from the Class 9 Structure of Atom worksheet can help students to boost their confidence. A perfect level of confidence can help students to improve the study process. 
• Assist the Preparation Process: Solving questions from the Class 9 Structure of Atom worksheet can help students in preparing for the chapter. 
• Helps in Self Evaluation: Through Structure of Atom worksheet, students can easily evaluate themselves. According to the self evaluation process, students can easily improve their preparation. 
• Builds a Strong Foundation: It is important for all students to solve questions from the chapter Structure of Atom. Regular solving questions from the worksheet can help students to build a strong foundation for the chapter Structure of Atom.  
• Enhances the Learning Process: Constant solving of questions from Structure of Atom Worksheet can enhance a student's learning process so that students can understand all topics easily.  
• Quick Revision: By solving questions from the Class 9 Structure of Atom worksheet, students can easily revise all the topics and concepts included in the chapter. 

Why Structure of Atom Worksheet Class 9 Is Right for You?

It is a must for students to exercise questions from Structure of Atom worksheet Class 9 as perfectly right for them. With the help of Structure of Atom worksheet Class 9 questions, students can increase their capability of solving questions in a different and creative manner.

Tips to Understand All Questions of Structure of Atom Worksheet Class 9 in a Better Way: 

Students should understand all questions of Structure of Atom worksheet Class 9 in a better way. Better understanding of questions can help students to score good marks in questions which are related to the chapter Structure of Atom. Those important tips are: 

• Finish Off The Chapter: First and foremost tip is to finish off the chapter Structure of Atom. Students need to complete each and every topic included in the lesson. 
• Practise Questions: After completing the chapter Structure of Atom, students need to practise questions from the Class 9 worksheet. Routine practice of questions can help students in identifying their strengths and weaknesses. 
• Note Down the Mistakes: While practising questions, it is very important that students note down their mistakes. Noting down the mistakes is very important as accordingly students can improve their preparation strategies. 
•  Correction of Mistakes: After noting down the mistakes, it is a must to correct all the mistakes made. Correction of mistakes can help students to solve worksheet questions in a better way. 
• Maintain a Positive Attitude: While solving questions from the Class 9 Structure of Atom worksheet, students need to maintain a positive attitude. A positive attitude can help students to remove stress and anxiety while preparing for the chapter Structure of Atom. 
• Remain Focused: To understand questions of Structure of Atom worksheet, students need to remain focused while preparing for it. 

Why Should Students Start Solving Structure of Atom Worksheet Class 9 From the PDF?

Structure of Atom Class 9 Worksheet is provided in the PDF so that students don’t need to search for them here and there. By solving the questions from Structure of Atom worksheet Class 9, students can understand the chapter in a fine way. Routine solving of questions from the Class 9 Science Worksheet can help students increase their comprehension skills. Comprehension skills will help in performing outstanding in the final examination. 

What are Included in Structure of Atom Worksheet Class 9?

In Structure of Atom worksheet Class 9, questions from the chapter are included. After solving questions of the chapter Structure of Atom, students can also go through the answers included in the worksheet. Answers to these questions of Structure of Atom are explained in a detailed manner. As it can also help teachers to make students understand in a better and elaborate way. Through this students can easily identify their skills and flaws for the Science chapter Structure of Atom.

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Structure of atoms class 9 worksheet

Fill in the blanks:

• According to Maharishi Kanad, the tiniest to tiny particle of a pure substance is called _________.
• An atom is the smallest unit of an element which takes part in a _________.
• Mass of an electron is 1/1837 times less than the mass of one atom of__________.
• The K-shell of any atom cannot have more than _________ electrons.
• Isotopes are the atoms of ___________ element, having same atomic number but different mass number.
• An atom of an element has 11 protons 11 electrons and 12 neutrons. The atomic mass of the atom is __________.
• Almost all the mass of an atom is concentrated in a small region of space called the _______.
• The subatomic particle not present in a hydrogen atom is________.
• Cathode ray are a beam of fast moving ______ .
• ________and________ more or less complexly make up the mass of an atom.
• The number of neutrons in the neutrons in the neutrons of an atom can be calculated by _______ the atomic number of _______its mass number.
• The isotopes of an element do not differ in the number of _______ but do differ in the number of _______.
• The type of radiations, which are not deflected in presence of electric or magnetic field are termed as rays.
• The penetrating power of B-rays is_______ times more than a-rays.
• Synthetic elements are those which are prepared by _________.
• The control rods in a nuclear reactor are made up of _________.
• _______ are stored in deep mines which are not in use.
• When an elements emits B-particle, its mass number________.
• Y-rays are________ radiations.
• The difference between the actual isotopic mass and the sum of masses of protons, neutrons and electrons is called_________.
• _______ are the best dombarding particles.
• ________ is used for the treatment of leukaemia.
• Chemical reactin
• Proton, neutron
• Subtracting, from
• Artificial transmutation
• Radioactive material
• Remains unchanged
• Electromagnetic
• Mass detect

True and False

• Radioactive isotope of iodine is used for making the medicine called tincture iodne.
• Thomson proposed that the nucleus of an atom contains protons and neutrons.
• J.J. Thomson proposed that the nucleus of an atom contains only nucleons.
• An electron has a mass that is much less than a proton.
• There is no particle of matter smaller than an atom.
• Atoms of an element may have more or less neutrons or electrons than other atoms of the same element.
• The innermost atomic shell can hold a maximum of 18 electons.
• B- Particles are fast moving electrons carrying negative charge.
• Nuclear chemistry has nothing to do with the electrons present in an atom.
• B- particles are nothing but electrons.
• a-particles are same thing as helium atoms.
• Out of a, B and y- rays travel with the highest speed and have highest ionizing power.
• A loss of B-particle result n the production of isobars.
• There is no difference between ‘artificial radioactivity’ and ‘induced radioactivity’.
• Iodine- 131 is used in the treatment of thyroid disorders.
• In a given electric field, B-particles are deflected more than a- particles in spite of a- particles having larger charge.

True / False:

Very Short anwer type

J. Chadwick

(a)Most of the space inside the atom is empty because most of the alpha-particles passed through the gold foil without getting deflected. (b)Very few particles were deflected from their path, indicating that the positive charge of the atom occupies very little space.

Short Answer type

Long answer type, foundation level.

This Structure of atoms class9 worksheet with answers is prepared keeping in mind the latest syllabus of CBSE . This has been designed in a way to improve the academic performance of the students. If you find mistakes , please do provide the feedback on the mail.

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CBSE Class 9 Science Atoms and Molecules assignment

Read and download free pdf of CBSE Class 9 Science Atoms and Molecules assignment. Get printable school Assignments for Class 9 Science . Class 9 students should practise questions and answers given here for Chapter 3 Atoms And Molecules Science in Class 9 which will help them to strengthen their understanding of all important topics. Students should also download free pdf of Printable Worksheets for Class 9 Science prepared as per the latest books and syllabus issued by NCERT, CBSE, KVS and do problems daily to score better marks in tests and examinations

Assignment for Class 9 Science Chapter 3 Atoms And Molecules

Class 9 Science students should refer to the following printable assignment in Pdf for Chapter 3 Atoms And Molecules in Class 9. This test paper with questions and answers for Class 9 Science will be very useful for exams and help you to score good marks

Chapter 3 Atoms And Molecules Class 9 Science Assignment

Sodium carbonate + ethanoic acid →sodium ethanoate + carbon + dioxide + water  

Exam Questions NCERT Class 9 Science Chapter 3  Atoms And Molecules

Question. Define law of conservation of mass. Ans :  Law of conservation of mass states that, ‘Mass is neither created nor destroyed in a chemical reaction.’

Question. Name the scientists whose experimentation established laws of chemical combination. Name the laws also. Ans :  Antoine Laurent Lavoisier and Joseph L. Proust experimented and established two laws of chemical combination. These laws are : (i) Law of conservation of mass, (ii) Law of constant proportions.

Question. Give one example each of (i) Monovalent cation, (ii) Bivalent cation, (iii) Monovalent anion, (iv) Bivalent anion. Ans :  (i) K+ or Na+          (ii) Mg+2 or Ca+2          (iii) F– or Cl–          (iv) O2– or S2–

Question. How can Dalton’s atomic theory explain the Law of Constant Proportions? Ans :  According to Dalton’s atomic theory, atoms of the same elements are same. Also atoms combine in whole number. This means that the atoms can combine with each other in a simple fixed ratio to form molecules.

Question. What is ion? Ans :  An ion is a charged particle. It can be positive or negative. Question. What do you mean by symbols of elements? Ans :  Each element is represented by a letter or group of two letters to write the chemical reactions conveniently. It is called symbol.

Question. How did the scientist lay the foundation of chemical sciences? Name the scientist. Ans :  Antoine Laurent Lavoisier laid the foundation of chemical science by establishing two important laws of chemical combination.

Question. An element has 8 electrons in its valence shell. What is its general name? Ans :  Noble gas.

Question. Write the names of the following compounds : (a) NiS (b) Mg(NO 3 ) 2 (c) Na 2 SO 4 (d) Al(NO 3 ) 3 (e) K3PO4 (f) Ca3N 2 Ans :  (a) Nickel sulphide,          (b) Magnesium nitrate,          (c) Sodium sulphate,          (d) Aluminium nitrate,          (e) Potassium phosphate,          (f) Calcium nitride.

Question Give the derivation source of symbol of sodium (Na). Ans :  The symbol of ‘Na’ for sodium is derived from its Latin name ‘Natrium’. Question. Give the full form of amu? Ans :  The full from of amu is atomic mass unit.

Question. Write the symbols of tungsten and iron. Ans :  (i) Tungsten (W) and          (ii) Iron (Fe)

Question. All elements have charged valency. Explain. Ans :  No, all elements do not form ions thus they, do not have a charge. For example : Carbon has a valency of 4 and nitrogen has a valency of 3. Non-metals are formed without a charged valency. Example : In carbon tetrachloride, carbon has valency of 4 and chlorine has a valency of 1.

Question. What are molecules? Give brief explanation of the arrangement of the constituent atoms in the molecules. Ans :  A molecule is the smallest particle of an element or compound which is stable in normal conditions. And it can freely show all the properties of that element or compound. It may be made up of one, two or more atoms. Molecule with one atom called monoatomic. E.g. helium, neon, etc. Molecule with two atoms called diatomic. E.g. Cl 2 , O 2 . Similarly, there are molecules containing three atoms (CO 2 ), four atoms (P4) and so on.

Q 1 144 grams of pure water is decomposed by passing electricity. 16 grams of hydrogen and 128 grams of oxygen are obtained. Which chemical law is illustrated by this statement? Q 2 What do you mean by Molar Mass ? Q 3 What is atomic mass unit ? Q 4 What are molecules? Q 5 What name is given to the number 6.023 x 10 23 ? Q 6 Name the building blocks of matter. Q 7 How many metres are there in 1 nanometer (nm) ? Q 8 Define atomicity. Q 9 Write the chemical formula of glucose. Q 10 Which subatomic particle was not present in Thomson‘s model of the atom? Q 11 Write the symbol of element lead and iron.

Q 12 Write down the formulae of aluminium sulphate and ethanol.

Q 13 What is the atomicity of – (a) Ozone (b) Nitrogen (c) Neon (d) Sulphur Q 14 Write the symbols of the following elements : a. Sodium b. Calcium c. Gold d. Iron Q 15 What weight (in grams) is represented by (a) 2 moles of CO 2 (b) 5 moles of NH3. Q 16 Define law of conservation of mass. Q 17 What is an atom ? Q 18 How many moles are there in 1 litre of water? Q 19 Write the chemical symbols of – (a) Silver (b) Potassium (c) Tin (d) Mercury Q 20 Write two differences between an atom and its ion. Q 21 What precentage of nitrogen is present in aluminium nitride? (Al = 27, N = 14) . Q 22 Calculate the number of moles for the following: (a) 12.046 x 10 23 number of He atoms (b) 56g of He Q 23 Write the formula of the following compound and name the elements present in them. (a) Ammonia (b) Sulphur dioxide (c) Ethanol (d) Methane Q 24 What do we call those species which have- (a) less electrons than the normal atoms. (b) more electrons than the normal atoms. Q 25 What is the mass of 5 moles of aluminium atoms? (Atomic mass of Al = 27 u) Q 26 How many times is a proton heavier than an electron? Write the absolute mass of a proton. Q 27 Which of the following are isotopes and which are isobars? Calcium, Protium, Argon, Deuterium Q 28 Calculate the mass of 0.8 mole of NaCl. (Atomic masses : Na = 23u; Cl = 35.5 u) Q 29 If one mole of oxygen atom weighs 16 grams, then what will be the mass (in grams) of 1 atom of oxygen? Q 30 Write the chemical formula of: (i) Nitogen oxide (ii) Barium nitride Q 31 (a) Calculate the molecular masses of (i) H 3 PO 4 (ii) H 2 O 2  (Atomic masses: H=1, O =16, P = 31) Q 32 Write the name of four elements which show variable valencies. Also write their valencies. Q 33 Calculate the mass of 6.022 x 10 24 atoms of carbon. Q 34 Calculate the mass of 1 molecule of Nitrogen. (Atomic mass of Nitrogen = 14)

Q 35 Calculate the number of molecules present in a drop of water weighing 0.75 g. (H = 1, O = 16) . Q 36 Write the formula of : (i) Ammonium sulphate (ii) Magnesium nitrate (iii) Aluminium bromide

Q 37 What do you understand by Formula Unit Mass? Calculate the formula unit masses of K2CO3 and ZnO. (Atomic masses of Zn = 65u, K = 39u, C = 12u) Q 38 An element X has a valency of 4 (a) What will be the formula of its chloride ? (b) What will be the formula of its sulphide ? (c) What will be the formula of its bromide? Q 39 Calculate the mass of 3.011 X 10 24 molecules of nitrogen gas. (Atomic mass of N = 14 u) Q 40 Distinguish between the molecule of an element and the molecule of a compound with the help of suitable example. Q 41 How many grams of hydrogen gas contain the same number of molecules as 22 grams of carbon dioxide gas? Q 42 What the following abbreviations stands for. (a) C (b) 2H (c) N 2 (d) 3N 2 (e) O 3 (f) O 2- Q 43 Write the name of the following compounds: (a) Ca 3 (PO 4 ) 2 (b) NaHCO 3 (c) (NH 4 ) 2SO 4 (d) MgCO 3 (e) FeSO 4 (f) AlCl 3 Q 44 The mass of an atom of element (Y) is 5.30 x 10 -23 g. (i) Calculate its atomic mass. (ii) Name this element. Q 45 Calculate the number of particles in each of the following: (i) 92g of Na atoms (ii) 7g of N 2 molecules (iii) 0.1 mole of oxygen atoms Q 46 Which of the following weighs the most? (i) 32g of oxygen (ii) 10g atoms of hydrogen (iii) 0.5 of iron (iv) 6.022 x 1022 atoms of C (Atomic mass: O =16, N = 14, Fe = 56, C = 12)

Marks (5) 

Q 47 Calculate the number of atoms of each type in 2.65 g of Na 2 CO 3 . Q 48 If 2 g of water contains z molecules, what will be number of molecules in 4 g of carbon dioxide? Q 49 (a) In 0.25 mol of P4, calculate (i) The number of P4 molecules (ii) The number of P atoms (iii) The number of moles of P atoms (b) Calculate the number of moles of magnesium in its 200 gram. (Atomic mass of Mg = 24 u) (c) Calculate the number of molecules present in 36 grams of water. Q 50 Calculate the number of chromium atom in 1.47 g of potassium dichromate (K 2 Cr 2 O 7 ) [Atomic mass: K = 39, Cr = 52, O = 16]. Q 51 Write any four significances of symbol. Give one example also. Q 52 Give the significance of the formula CO 2 . Q 53 (i) Write the atomicity of the following: (a) Ozone (b) Chlorine (c) Helium (d) Sulphur (e) Oxygen (f) Phosphorous (ii) Give one word answer The Latin name of iron from which its symbol is derived. An atom or group of atom having positive charge.

Most Important Questions

Q 1 State main points of Dalton atomic theory.

Q 2 State the law of constant proportion.

Q 3 state the law of conservation of mass

Q 4 If 90g of pure water is obtained through 80g of oxygen and Xg of hydrogen. a. Find the value of X. b. Which chemical law is illustrated by this statement?

Q 5 Calculate the molecular mass of the following: a. H 2 O b. HCl c. H 2 S

Q 6 If 6g of hydrogen combine with 48g of oxygen, how many grams of water is obtained?

Q 7 If carbon and oxygen combine in a definite ratio of 3:8 to form carbon dioxide. What mass of oxygen gas is required in carbon dioxide with 10 g of carbon?

Q 8 Give symbol of the followinga. oxygen b. hydrogen c. carbon

Q 9 If atomic mass of carbon is 1u then what is the atomic mass of nitrogen (N = 14, C = 12) ?

Q 10 Identify the anions, cations and charge present on them in following molecules: HCl , NaCl , H 2 O , Al 2 O 3

Q 11 Write the chemical formula of the following: a. Oxygen b. Carbon dioxide c. Ammonia d. Calcium carbonate

Q 12 Give the names of the following compounds: a. H 2 SO 4 b. He c. CO

Q 13 Write the formula unit mass of the following: a. NH 3 b. CO 2 c. K 2 Cr 2 O 7 d. SO 2 e. C 12 H 22 O 11

Q 14 Calculate the mass in grams of 0.8 mole of CO 2.

Q 15 In which of the following cases the number of hydrogen atoms is more? a. One mole of CH 4 b. Two mole of NH 3

Q 16 Calculate the number of molecules in 20g of water.

Q 17 How many moles are present in 6g of sulphuric acid?

Q 18 What is the number of molecules in a drop of water weighing 0.2g?

Q 19 Calculate the number of S atoms in 2 mole of S8

Q 20 How many moles are there in 70g of potassium dichromate,( K 2 Cr 2 O 7 ) ?

Q 21 How many moles of calcium carbonate are present in its 5g ?

Q 22 What mass of hydrogen chloride, (HCl) , will contain the same number of molecules as in a. 6.022 x 10 23 molecules of water b. 2.0 g of methane, CH 4

CBSE Class 9 Science Chapter 3 Atoms And Molecules Assignment

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CBSE Worksheet for 4 Structure Of Atom class 9

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BOARD: CBSE

Chemistry Worksheet - 4

TOPIC: Structure Of Atom

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STRUCTURE OF ATOM

Summar y –.

• Discovery of electron, proton.
• Thompson’s model of atom.
• Rutherford’s model of atom and its defects.
• Discovery of neutron.
• Comparison of charge and mass of electron, proton and neutron.
• Bohr’s model of atom.
• Atomic number, mass number and electronic configuration.

SECTION – 1

• A proton is 1837 times heavier than an electron.
• A proton is 1/1837 times heavier than an electron.
• A proton is 1837 times lighter than an electron.
• Proton has the same mass as an electron.

• both A) and B)
• Alpha particles are much heavier than electron.
• Alpha particles are positively charged.
• Most part of the atom is empty.
• Alpha particles move with high velocity.

• They have isobars.
• Their isotopes have non-integral masses.
• They have isotopes.
• The constituents neutrons, protons and electrons combine to give fractional masses.
• isotope of oxygen
• isobar of oxygen
• isotope of carbon
• isobar of carbon
• 1.673 × 10 -24 gm
• 1.673 × 10 -27 Kg
• The most of the space inside the atom is empty.
• The volume of the nucleus is very small.
• Ar (40) and Ca (40) have the same mass number but their properties are entirely different. Why ?
• Define atomic number. Why is it called the main characteristic property of the elements ?
• Who proposed the existence of neutron and what was the basis of this assumption ?
• What type of information is obtained about the atom by Rutherford particle scattering experiment ?
• What are isotopes ? Give one example.
• Give the application of isotopes in industry and in medicine

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Class 9 Chemistry Chapter 4 - Structure of the Atom Important Questions with Answers

Class 9 chemistry important questions with answers are provided here for Chapter 4 – Structure of the Atom. These important questions are based on CBSE board curriculum and correspond to the most recent Class 9 chemistry syllabus. By practising these Class 9 important questions, students will be able to quickly review all of the ideas covered in the chapter and prepare for the Class 9 Annual examinations.

Download Class 9 Chemistry Chapter 4 – Structure of the Atom Important Questions with Answers PDF by clicking on the button below. Download PDF

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Structure of atom in one shot (a to z) class 9 chemistry.

Class 9 Chemistry Chapter 4 – Structure of the Atom Important Questions with Answers

Short answer type questions.

Q1: Is it possible for the atom of an element to have one electron, one proton and no neutron. If so, name the element.

Yes, this is true for hydrogen’s common stable isotope (protium), which is denoted by the letter \(\begin{array}{l}_{1}^{1}\textrm{H}\end{array} \) .

Q2: Write any two observations which support the fact that atoms are divisible.

The discovery of electrons and protons serves to strengthen the idea that atoms are divisible. During a chemical reaction, electrons are transferred or shared between distinct atoms, leading atoms to rearrange.

Q3: Will 35 Cl and 37 Cl have different valencies? Justify your answer.

The number of protons or electrons is equal to the valency. Since both chlorine 37 and chlorine 35 have the same number of protons and electrons, they have the same valency.

Chlorine 37 and chlorine 35 are identical isotopes. As a result, they have the same atomic number but have different masses. Their mass numbers differ due to the different amount of neutrons in each of them.

Q4: Why did Rutherford select a gold foil in his α–ray scattering experiment?

Rutherford wanted a metal sheet that could be as thin as possible for the scattering experiment. Gold is the most malleable of all the metals known to man. It’s simple to make thin sheets out of it. As a result, for his alpha-ray scattering experiment, Rutherford used gold foil.

Q5: Find out the valency of the atoms represented by the Fig. 4.3 (a) and (b).

Atom (a) has zero valency because it has established a stable configuration with 8 electrons in the valence shell.

The valency of atom (b) is 1 since the valence shell contains 7 electrons. In order to obtain a stable (octet) configuration, atom (b) can take one additional electron.

Q6: One electron is present in the outer most shell of the atom of an element X. What would be the nature and value of charge on the ion formed if this electron is removed from the outer most shell?

When an electron is removed from the outermost shell, a cation is formed, and the element’s charge is increased to +1.

When a single electron from the outermost shell of an element X is removed, the atom loses its negative charge and becomes a positively charged ion with a charge of +1.

The net charge on the ion will be equal to the amount of charge present on one electron.

Q7: Write down the electron distribution of chlorine atom. How many electrons are there in the L shell? (Atomic number of chlorine is 17).

Chlorine has an atomic number of 17. As a result, the innermost shell contains 2 electrons, the second shell has 8 electrons, and the outermost shell has 7 electrons.

K shell – 2 electrons

L shell – 8 electrons

M shell – 7 electrons

The electron configuration of chlorine can be written as 1s 2 2s 2 2p 6 3s 2 3p 5 or as [Ne]3s 2 3p 5 .

Q8: In the atom of an element X, 6 electrons are present in the outermost shell. If it acquires noble gas configuration by accepting requisite number of electrons, then what would be the charge on the ion so formed?

The electronic configuration of a noble gas is 2,8. It possesses 8 electrons in its outermost orbitals. Element X contains 6 electrons in its outermost shell. Two more electrons are required to obtain the noble gas configuration. As a result, in order to achieve a noble gas configuration, the element should take two electrons, resulting in a charge of -2.

Q9: What information do you get from the Fig. 4.4 about the atomic number, mass number and valency of atoms X, Y and Z? Give your answer in a tabular form.

Atomic number, mass number and valency of atoms X, Y and Z.

Q10: In response to a question, a student stated that in an atom, the number of protons is greater than the number of neutrons, which in turn is greater than the number of electrons. Do you agree with the statement? Justify your answer.

The provided statement is not correct.

According to this comment p > n > e.

The number of protons, on the other hand, is never greater than the number of neutrons.

Because mass number is equal to double the atomic number or greater than double the atomic number, the number of neutrons might be equal to or greater than the number of protons.

Because the number of electrons equals the number of protons in the neutral atom, the number of neutrons can be more than the number of electrons.

Q11: Calculate the number of neutrons present in the nucleus of an element X which is represented as 31 X 15 .

Mass number (A) = No. of protons (Z) + No. of neutrons

Given, the mass number as 31 and the number of protons is 15.

No. of protons (Z) + No. of neutrons = 31

∴ Number of neutrons = 31 – number of protons

⇒ Number of neutrons = 31 – 15 = 16 .

Q12: Match the names of the Scientists given in column A with their contributions towards the understanding of the atomic structure as given in column B.

(a) Ernest Rutherford – (iii) Concept of the nucleus

(b) J.J.Thomson – (iv) Discovery of electrons

(c) Dalton – (i) Indivisibility of atoms

(d) Neils Bohr – (ii) Stationary orbits

(e) James Chadwick – (vi) Neutron

(f) E. Goldstein – (vii) Canal rays

(g) Mosley – (v) Atomic number

Q13: The atomic number of calcium and argon are 20 and 18 respectively, but the mass number of both these elements is 40. What is the name given to such a pair of elements?

They are called isobars.

Isobars have different atomic numbers (or protons), but the same mass number.

Q14: Complete Table 4.1 on the basis of information available in the symbols given below.

(a) 35 17 Cl

(c) 81 35 Br

Q15: Helium atom has 2 electrons in its valence shell but its valency is not 2, Explain.

Electronic arrangement of a helium atom is 1s 2 which contains two valence electrons, but because it does not form a chemical bond, its duplet is complete. As a result, valency is zero.

Q16: Fill in the blanks in the following statements:

(a) Rutherford’s α-particle scattering experiment led to the discovery of the _______.

(b) Isotopes have same ________ but different________.

(c) Neon and chlorine have atomic numbers 10 and 17 respectively. Their valencies will be _______ and ________ respectively.

(d) The electronic configuration of silicon is _______ and that of sulphur is ________.

a) Rutherford’s α-particle scattering experiment led to the discovery of the atomic nucleus .

b) Isotopes have same atomic number but different mass number .

c) Neon and chlorine have atomic numbers 10 and 17 respectively. Their valencies will be 0 and 1 respectively.

d) The electronic configuration of silicon is 2.8.4 and that of sulphur is 2.8.6

Q17: An element X has a mass number 4 and atomic number 2. Write the valency of this element.

Mass number = 4

Atomic number = 2

X is Helium.

It has 0 valency and it would not react with any other atom because it has its outer shell filled.

Long Answer Type Questions

Q1: Why do Helium, Neon and Argon have a zero valency?

An element’s valency is its ability to combine. The valency of noble gases is zero since there are no free electrons in the valence shell and the elements are already in a stable state.

• The outermost orbit of helium has two electrons, filling shell 1 and generating a duplet arrangement in the valence shell.
• The valence orbit of neon has eight electrons, completing the duplet structure.
• The outermost layer of Argon and Neon has 8 electrons, completing the octet arrangement.

Because these elements have the most electrons in their valence shell, they have a stable electron configuration and do not participate in chemical reactions.

Q2: The ratio of the radii of hydrogen atom and its nucleus is ~ 10 5 . Assuming the atom and the nucleus to be spherical,

(i) What will be the ratio of their sizes?

(ii) If atom is represented by planet earth ‘Re’ = 6.4 ×10 6 m, estimate the size of the nucleus.

Assuming the atom and the nucleus to be spherical,

(i) Atomic size is represented in terms of atomic radius

Volume of the sphere = \(\begin{array}{l}\frac{4}{3}\pi r^{3}\end{array} \) \(\begin{array}{l}V_{H} = \frac{4}{3}\pi r_{H}^{3}\end{array} \) ………………….. (1)

Ratio of volumes

\(\begin{array}{l}\frac{V_{H}}{V_{n}} = 10^{15}\end{array} \)

(ii) If an atom is represented by planet earth ‘Re’ = 6.4×10 6 m, then the radius of the nucleus would be r n .

\(\begin{array}{l}r_{n} = 64m\end{array} \)

Q3: Enlist the conclusions drawn by Rutherford from his α-ray scattering experiment.

The α-particle scattering experiment led Rutherford to the following conclusions:–

(i) Because most α-particles travelled through the gold foil with no deflection, most of the space inside the atom was unoccupied.

(ii) The positive charge occupied very little space inside the atom, as just a few particles were deviated from their route.

(iii) Only a small percentage of α-particles were deflected by 180°, implying that the positive charge and mass of the gold atom are concentrated in a compact volume within the atom.

(iv) He also computed that the radius of the nucleus was approximately 105 times smaller than the radius of the atom based on the data.

Q4: In what way is the Rutherford’s atomic model different from that of Thomson’s atomic model?

Rutherford proposed a model in which the electrons moved in well-defined orbits around the nucleus. An atom has a positively charged centre (later named the “nucleus”). He also proposed that the nucleus is very small in comparison to the size of the atom, and that the nucleus contains nearly all of an atom’s mass.

Thomson recommended that the atom be modelled after a Christmas pudding. The electrons are scattered about like currants in a positively charged pudding spherical, and the atom’s mass was expected to be evenly distributed.

Q5: What were the drawbacks of Rutherford’s model of an atom?

Rutherford carried out an experiment in which he bombarded a thin sheet of gold with -particles and then analysed the trajectory of the particles after they collided with the gold foil.

• Rutherford’s atomic model could not explain how the moving electrons were able to maintain their orbit.
• Any charged particle would give forth energy during acceleration, lose energy while revolving, and eventually fall into the nucleus.

Q6: What are the postulates of Bohr’s model of an atom?

The following are the postulates of Bohr’s atom model:

1. Electrons circle the nucleus of an atom in a fixed path known as the orbit or stationary state of the shell.

2. The shells have varying energy levels, represented by the letters K, L, M, and N.

3. The electron does not absorb or release energy as long as it is in an orbit.

4. The electron can only move in orbits where angular momentum is quantized, that is, where the electron’s angular momentum is an integral multiple of h/2𝜋 .

Q7: Show diagrammatically the electron distributions in a sodium atom and a sodium ion and also give their atomic number.

The atomic number (Z) of an element is equal to the number of protons in its atom.

Atomic number of sodium (Z) = 11 and Mass number of sodium (A) = 23

Number of protons in the nucleus = 11

Number of neutrons in the nucleus = 23 − 11 = 12

Number of electrons = 11

Thus, electronic configuration of Na-atom = 2, 8, 1(K,L,M)

An electron is lost from the sodium atom(present in the outermost shell), resulting in the formation of the Na+ ion.

Hence, the electronic configuration is 2, 8(K, L). However, the number of protons and neutrons remains the same.

Q8: In the Gold foil experiment of Geiger and Marsden, that paved the way for Rutherford’s model of an atom, ~ 1.00% of the α-particles were found to deflect at angles > 50°. If one mole of α-particles were bombarded on the gold foil, compute the number of α-particles that would deflect at angles less than 50°.

% of α-particles deflected more than 50° = 1% of α-particles.

∴ % of α-particles deflected less than 50° = 100 – 1 = 99%

Number of α-particles bombarded = 1 mole = 6.022 × 10 23 particles

∴ Number of particles that deflected at an angle less than 50° = 99/100 × 6.022 × 10 23

= 5.96 × 10 23

CBSE Class 9 Science Chapter 4 MCQs

1. _______discovered the electron.

(a) Chadwick

(b) Rutherford

(c) Thomson

(d) Goldstein

Answer: (c) Thomson

2. What property of an element determines its chemical behaviour?

(a) Valency of an element

(b) Size of an element

(c) Molar mass of the element

(d) None of the above

Answer: (a) Valency of an element

3. _______ is the radioactive element used in the treatment of cancer.

(a) Iodine-131

(b) Uranium-234

(c) Plutonium-239

(d) Cobalt-60

Answer: (d) Cobalt-60

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NCERT Solutions for Class 9 Science Chapter 4 - Structure of the Atom - eSaral

Download The PDF of NCERT Solutions for Class 9 Science Chapter 4 "Structure of the Atom"

Important topics of class 9 Science Chapter 4

• Structure of Atom
• Charged Particles in Matter
• How are Electrons Distributed in Different Orbits
• Atomic Number and Mass Number

All Questions of Chapter 4

Once you complete the chapter 4 then you can revise it by solving following questions.

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• STUDY MATERIAL FOR CBSE CLASS 9 CHEMISTRY
• Chapter 1 - Atoms and Molecules
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• Chapter 4 - Matter In Our Surroundings