Compare the radius of the nucleus with that of the atom. (а) Name the elements which has 22 neutrons in nucleus. Bohr put forward the following postulates in order to overcome the objections raised against Rutherford s atomic method: . Is this an atom of a metal, non-metal or noble gas? Any particle in a circular orbit would undergo acceleration. Therefore, the valency of Na is 1. (i) Sodium ion (Na+) Calculate the number of electrons, protons and neutrons in the following species: Define atomic number. Question 6. Question 6. (b) The valency of element A. No. Helium has two electrons in its only energy shell, while Argon and Neon have 8 electrons in their valence shells. Answer: Correct Option is : 4. of electrons = Z = 35 (b) What are the postulates of Bohr’s model of an atom? (c) Elements A and B have atomic numbers 18 and 16 respectively. [NCERT Exemplar] of protons + No. Many scientists contributed in revealing the presence of charged particles in an atom. Assertion Reason Based Questions A ssertion and Reasoning based questions are bit tricky. of protons = No. (c) Rutherford model of atom could not provide stability to the nucleus. are isotopes. Answer: Hence the valency is zero. Number of electrons = 12 – 2 = 10 Now, for a neutral atom, Atomic number = Number of protons = Number of electrons. CBSE Worksheets for Class 9 Chemistry: One of the best teaching strategies employed in most classrooms today is Worksheets. (i) The element with atomic number 56 is Ba. Hence, they are called stationary states (stationary means fixed). 33A14 and 37C17? An element with mass number 81 contains 31.7% more neutrons as compared to protons. What is the charge on alpha particle? As these have maximum number of electrons in their valence shells, they do not have any tendency to combine with other elements. Thus, the revolving electrons would lose energy and finally fall into the nucleus. (b) (i) 2,8, 7 Extra Questions for Class 9th: Ch 4 Structure of the Atom. Question 11. (b) How are the canal rays different from electron in terms of charge and mass? of nucleons (protons + neutrons) present in the nucleus What are the actual values of charge and mass of the electron? (e) The element with Z = 13 is aluminium (Al) Out of proton and neutron, which is heavier? Mass number, A = 80 Question 8. Answer: (ii) K+ ion, because it has atomic number = 19 and mass number = 39. Therefore, the valency of Na is not 7. Extra Questions for Class 9 Science Chapter 4 Structure of the Atom with Answers Solutions, Question 1. Canal rays. Solution : In an atom, the mass number of an atom is equal to number of nucleons. (b) the atomic masses of elements are in fractions? Question 12. Explain. of electrons = 13 State three features of the nuclear model of an atom put forward by Rutherford. They have same number of protons but different number of neutrons in their nuclei. Given that natural sample of iron has isotopes \(_{ 54 }^{ 28 }{ Fe }\), \(_{ 58 }^{ 28 }{ Fe }\) and \(_{ 57 }^{ 28 }{ Fe }\) in the ratio of 5%, 90% and 5% respectively. SOLUTION: Mass number of helium = 4 Number of protons = 2 Number of neutrons (n) = Mass number (A) – No. NCERT Solutions of Chapter 4 Structure of the Atom, CBSE Previous Year Question Paper for Class 10, CBSE Previous Year Question Paper for Class 12. Mass number = No. Mention the postulates Neils Bohr put forth to overcome the objections raised against Rutherford’s atomic model. Symbol = \(_{ 56 }^{ 26 }{ Fe }\)3+. What is the name given to such a pair of elements? is same but atomic no. Register online for Science tuition on … Answer: An element X has a mass number 4 and atomic number 2. Hydrogen has three isotopes. (ii) While revolving in discrete orbits the electrons do not radiate energy. = 31 – 15 Question 30. Number of α – particles bombarded = 1 mole = 6.022 x 1023 particles Atom A has a mass number 238 and atomic number 92 and atom B has mass number 235 and atomic number 92. Answer: Answer: Question 36. (a) The orbital revolution of the electron is not excepted to be stable. Do the elements \(_{ 3 }^{ 1 }{ X }\) and \(_{ 3 }^{ 2 }{ Y }\) represent pair of isotopes? (c) \(_{ 40 }^{ 20 }{ Ca }\) 1 MARK QUESTIONS Question. of protons = 12 (Given) (c) B and C Calculate the atomic number and mass number of the element Y. (a) The anode rays produced at the anode of the discharge tube are called canal rays because they pass through the holes of the cathode. The valence shell of atom may or may not have 8 electrons. (b) Electrons are negatively charged and their mass is approximately 1/2000 of that of canal rays. He also proposed that the size of the nucleus is very small as compared to the size of the atom and nearly all the mass of an atom is centred in the nucleus. Write the valency of this element. Hydrogen atom is made up of only one electron and one proton. \(_{ 58 }^{ 26 }{ A }\), \(_{ 58 }^{ 28 }{ B }\) are iso¬bars, as mass no. Give one example. of neutrons = A – No. Electronic configuration of Na = 2, 8, 1. Question 16. A, B and D have completely filled valence shells, i.e., either 2 or 8 electrons in their valence shells. (ii) the nucleus with atomic number 26 and mass number 55. Rutherford selected a gold foil in his a-ray scattering experiment because gold has high malleability. [NCERT Exemplar] All types of questions are solved for all topics. (iii) A very small fraction of a-particles were deflected by 180°, indicating that all the positive charges and mass of the gold atom were concentrated in a very small volume within the atom. It will be dealt in higher classes. Mass numbers: P = 31; Mg = 24 Answer: (ii) Very few particles deviated by small angles from their path which suggested that nucleus is positively charged. Class 9 Science Notes Chapter 4 STRUCTURE OF THE ATOM Contribution to the Atomic theory Timeline • More than 2400 years ago, he named the smallest piece of matter “ATOMOS ,” meaning “not to be cut.” To Democritus, • Atoms were small, hard particles that were all made of the same material but were different shapes and sizes. Answer: Answer: NCERT 9th Class (CBSE) Science: Structure of the Atom Quiz. Both helium (He) and beryllium (Be) have two valence electrons. Mass = 9.11 x 10-31 kg (1/1840th of the mass of hydrogen atom). of protons = 9 Answer: Answer: An atom has a center called nucleus; Compared to the size of an atom the size of the nucleus is very smell SUPPORT OUR WORK / DONATE :- https://tinyurl.com/Donate-EdumantraSTRUCTURE OF ATOM (FULL CHAPTER) | CLASS 9 CBSE, THOMSON'S ATOMIC … Mass number of the element = Number of protons + Number of neutrons = 15 + 16 = 31 of protons = A In the atom of an element X, 6 electrons are present in the outermost shell. The discovery of subatomic particles led to a revolution in the study of matter. of electrons = 18 (Given) of electrons = Z = 8 Number of neutrons = 31 – 15 = 16, (iii) Magnesium ion (Mg2+) MCQ Questions for Class 9 Science with Answers were prepared based on the latest exam pattern. ∴ Fraction of the volume of atom occupied by the nucleus Answer: How many protons, electrons and neutrons are there in the following nuclei? ∴ Number of neutrons = 31 – number of protons Chapter covers the topics like Thomson’s model, Rutherfords’s model, Bohr’s model, distribution of electrons, valency, atomic number, mass number, isotopes, isobars and more. Hence, maximum number of electrons that can be present in M-shell = 2n2 = 2 x 32 = 18. (b) Atomic number of an element Y is 17. Answer: 33A17, 40B20, 37C17, 38D19. Failure of Dalton’s Atomic Theory. (iii) The energy of orbit closest to the nucleus is lowest and farthest away is highest. Out of C-12 and C-14 isotopes of carbon, which is of radioactive nature? Q3. No. Calculate its atomic number and its atomic mass. Mass no. (b) The postulates put forth by Neils Bohr’s about the model of an atom: Who identified the sub-atomic particle electron? Same mass number but different atomic numbers. You can find other Structure Of Atom - Practice Test, Class 9 Science extra questions, long questions & short questions for Class 9 on EduRev as well by searching above. Both the species are the isotopes of the same element i.e., the carbon. (i) Protons in atoms A and B = 92 (ii) \(_{ 79 }^{ 35 }{ X }\), \(_{ 80 }^{ 35 }{ Y }\) (f) It is a metal. Name the particle and give its location in an atom. No. An atom of an element has three electrons in its 3rd orbit, which is the outermost shell. Show diagrammatically the electron distributions in a sodium atom and a sodium ion and also given their atomic number. Answer: [NCERT Exemplar] Who discovered it ? of protons = No. = 1.304x No. Name the particle and give its location in the atom. It contains 7 electrons. of electrons = 13 Thus, most of the space in an atom was thought to be empty. (ii) \(_{ 25 }^{ 12 }{ Mg }\) = 15 Answer: Question 2. Isobars are the atoms of different elements which have different atomic numbers but same mass number. = \(\frac { 99 }{ 100 }\) x 6.022 x 1023 Mass no. [NCERT Exemplar] If bromine atom is available in the form of, say, two isotopes 79 35 Br (49.7%) and 81 35 Br (50.3%), calculate the average atomic mass of bromine atom. No, they do not because the two elements differ in their atomic numbers. Write the electronic configurations of the following elements and write the number of valence electrons present in it. Atom is the smallest unit of matter which takes part in a chemical reaction. (b) What is its valency and why? Pre Foundation Question banks are helpful for students aspiring for NTSE, Olympiad, KVPY, IIT JEE, Medical and other engineering and competitive exams. (iii) Valency is 2 (+2) Explain Rutherford’s α-particle scattering experiment and give its observation and conclusion … There is a positively charged center in an atom called the nucleus. (c) Atomic number of element B is 16. is different. Answer: Answer: (iv) No. Identify the isotopes out of A, B, C and D? Assuming the nucleus and the atom to be spherical, what fraction of the atomic volume is occupied by the nucleus? He2+ ion has no electrons. The number of electrons in the outermost ‘L’ shell of an atom is 5. Why are Bohr’s orbits called stationary states? Answer: Its symbol is \(_{ 56 }^{ 26 }{ Fe }\), (iii) The element with atomic number 4 is Be. Answer It is the number of protons in the nucleus of an atom. Since, sodium atom and sodium ion contain the same number of protons, therefore, the atomic number of both is 11. No, 35Cl and 35Cl are isotopes of an element. Answer: Volume of the atom = 4 πR3/3 = 4π (10-8)3/3 cm3 The given element Y with atomic number 15 is phosphorus. (a) Give the electronic distribution of element B. What is an electron ? [NCERT Exemplar] Mass of electron is 1/1840 times that of a proton. (i) Only certain special orbits known as discrete orbits of electrons, are allowed inside the atom. (ii) \(_{ 25 }^{ 12 }{ Mg }\) = 55.95 u. Answer: = \(\frac { 596.178 }{ 100 }\) x 1023 ∴ Number of protons = Atomic number = 92 Answer: Question 5. Question 1. (a) New radiations in a gas discharge tube which are positively charged. The nuclear radius is of the order of 10-13 cm while atomic radius is of the order 10-8 cm. of electrons = 23 Similarly, Answer: Na+ has completely filled K and L shells. No. The atomic number of an element is equal to the number of protons in its atom. Q1. C-14 isotope is of radioactive nature. Since the iron carries 3 units of positive charge, it will have 3 electrons less than the number of protons. Helium atom has an atomic mass of 4 u and two protons in its nucleus. (a) Electronic configuration: 2, 8, 3 Its symbol for \(_{ 9 }^{ 4 }{ Be }\), Question 10. The valency of the element is 3. of electrons = 12 – 2 = 10 Atomic number of the element = 16 In an atom the number of protons and electrons is always equal. Question 4. of neutrons = 16 (Given) Do isobars have also identical chemical characteristic like isotopes? (d) Mass number of element D is 39. No. The Class 11 Chemistry Chapter 2 important questions deals with the questions in the chapter Structure of Atom and hence is a really good addition to the syllabus for the students of class 11. Here you can get NCERT Extra Questions for Class 9 Science with Answers. Let R be the radius of the atom and r be that of the nucleus. 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