Class 9th Chemistry Unit 2 Question And Answer
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Q1. What is the nature of charge on cathode rays?
Ans: Cathode rays are negatively charged particles. J.J. Thomson discovered the e/m (change/mass) ratio of cathode rays and found it equal to electron.
Q2. Give five characteristics of cathode rays.
Ans: The Characteristics of cathode rays are as: i. These rays travel in straight line perpendicular to the cathode surface. ii. They can cast a sharp shadow of an opaque object if placed in their path. iii. They raise temperature of the body on which they fall. iv. J.J. Thomson discovered their e/m ratio. V. Light is produced when these rays hit the sides of the discharge tube.
Q3. Differentiate between shell and sub-shell with example.
Ans: Difference between Shell and Sub Shell can describe as: Shell: Each principle energy level is called Shell and these are represented by K, L, M, N Sub Shell: Each shell further contains one or more sub shells. These are represented by s, p, d, f.
Q4. What will be the nature of charge on an atom when it loses an electron or when it gains an electron?
Ans: When an atom loses an electron, it acquires positive charge due to more number of protons in the nucleus
Q5. A patient has goiter, how will it be detected?
Ans: Isotopes of iodine-131 are used for diagnosis of goiter in thyroid gland.
Q6. Give three properties of positive rays.
Ans: (i) They travel in straight line in a direction opposite to cathode rays. (ii) Their deflection in electric and magnetic field proved that these were positively charged. (iii) Mass of these particles was found equal to that of proton or simple multiple of it.
Q7. What are the defects of Rutherford’s atomic model?
Ans: It had following defects: (i) According to classical theory, electrons being the charged particles should release or emit energy continuously and they should ultimately fall into the nucleus. (ii) If the electrons emit energy continuously, they should form a continuous spectrum but in fact, line spectrum was observed.
Q 8. As long as electron remains in an orbit; it does not emit or absorb energy. When does it emit or absorb energy? The energy is emitted or absorbed only when an electron jumps from one orbit to another. When
Ans: an electron jumps from lower orbit to higher orbit it absorbs energy and when it jumps back from higher orbit to lower orbit, it radiates energy. This change in given by following Planck’s ” s equation.
Q 9. Define plum pudding model. Who presented it?
Ans: Thomson put forth his plum pudding theory. According to this theory. Atoms are solid structures of positively charge with tiny negative particles stuck inside. It is like plums in the pudding.
Q 10. Who discovered neutrons and how?
Ans: Chadwick discovered neutrons in 1932. He bombarded beryllium with alpha particles. He observed that highly penetrating radiations were produced. These rays were called neutrons.
Q 11. Write three properties of neutrons.
Ans: The properties of neutrons are as: I. Neutrons carry no charge. II. They are highly penetrating. III. Mass of neutrons are nearly equal to the mass of proton.
Q 12. Write down the electronic configuration of Clion.
Ans: Chlorine has 17 electrons while chloride (CI) ion has 17+1=18 electrons. Therefore, its electronic configuration will be:
Q 13. An element has 5 electrons in M shell. Find out its atomic number.
Ans: To have 5 electrons in M shell means its K and L shell are completely filled. Hence its electronic configuration will be
Q 14. Define isotopes.
Ans: Atoms of an element that have same atomic number but different atomic masses are called isotopes e.g. Hydrogen has three isotopes
Q 15. Write use of Co-60.
Ans: Cobalt-60 emits strongly penetrating gamma rays and hence used for cancer affecting within the body.
Q 16. Define radioactive-isotope dating.
Ans: The age determination of very old objects based on the half-lives of the radioactive isotope is called radioactive-isotope dating.
Q17. What is meant by radio carbon dating or carbon dating?
Ans: This is an important method of age determination of old carbon containing objects (fossils) by measuring the radioactivity of C-14 in them is called radio-carbon dating or simply carbon dating.
Q18. What is Dalton’s atomic theory?
Ans: In the beginning of 19″ century John Dalton put forward atomic theory. This theory describes that: a. All matter is made up of very small indivisible particles called atoms. b. An atom is indivisible, hard, dense sphere. c. Atoms of same element are alike. d. They combine in different ways to form compounds
Q 19. Write contribution of J.J. Thomson.
Ans: J.J. Thomson (1856-1940) was a British physicist. He was awarded the 1906 Noble Prize in Physics for the discovery of electron and for his work on the conduction of WN electricity in gases.
Q 20. What is meant by plum pudding Model?
Ans: Thomson put forth his “plum pudding” theory. He postulated that atoms were solid structures of positively charge with tiny negative particles stuck inside. It is like plums in the pudding.
Q 21. Write contribution of Sir William crooks.
Ans: Sir William Crooks (1832-1919) was a British chemist and physicist. He was pioneer of vacuum tubes. He worked on spectroscopy.
Q 22. Write the contribution of Rutherford.
Ans: Rutherford was a British-New Zealand chemist. He performed a series of experiments using alpha particles. He won the Nobel Prize in Chemistry in 1908. In 1911, he proposed the nuclear model of the atom and performed the first experiment to split the atom. Because of his great contributions, he is considered the father of nuclear science.
Q 23. Write the contribution of Neil Bohr.
Ans: Neil Bohr was s a Danish physicist who joined F IR Rutherford in 1912 for his post-doctoral research. In 1913, Bohr presented his atomic model based on Quantum theory. He won the 1922 Noble Prize for Physics for his work on the structure of an atom.
Q 24. What is meant by Quantum?
Ans: Quantum means fixed energy. It is the smallest amount of energy that can be emitted or absorbed as electromagnetic radiation. Quanta are plural of quantum.
Q25. Write contribution of max Planck.
Ans: In 1918 Noble prize in physics was awarded to German physicist Max Planck (1858-1947) for his work on the quantum theory
Q 26. What is the maximum number of electrons that can be accommodated in p-subshell?
Ans: p-subshell can accommodate maximum six electrons.
Q 27. How many subshells are there in second shell?
Ans: There are two subshells are present in second shell that is s and p subshells.
Q 28. Why does an electron first fill 2p orbital and then 3s orbital?
Ans: An electron first fill 2p orbital because the electrons fill the shells in order of their increasing energy, i.e. lower energy level is occupied first then the higher energy level. So 2p orbital as lower energy level then 3s orbital.
Q 29. If both K and L shells of an atom are completely filled what is the total number of electrons present in them?
Ans: There are 10 total number of electrons present in K and L shells.
Q 30. How many electrons can be accommodated in M shell?
Ans: M shells can accommodate maximum 18 electrons.
Q 31. What is the electronic configuration of hydrogen atom?
Ans: The electronic configuration of hydrogen atom is: Is¹
Q 32. What is atomic number of phosphorus? Write down its electronic configuration.
Ans: The atomic number of phosphorus is 15 and its electronic configuration.
Q 33. If an element has atomic number 13 and atomic mass 27; how many electrons are there in each atom of the element?
Ans: There are 13 electrons are present in each atom of the element.
Q 34. How many electrons will be in M shell of an atom having atomic number 15.
Ans: There are 5 electrons present in M shell.
Q 35. What is maximum capacity of a shell?
Ans: The maximum capacity of shells to accommodate the electrons is as following: K shell can accommodate 2 electrons. L shell can accommodate 8 electrons. M shell can accommodate 18 electrons. N shell can accommodate 32 electrons.
Q 36. How was it proved that the whole mass of an atom is located at its center?
Ans: Rutherford observed that atomic mass of the element could not explained on the basis of the masses of electron and proton only. He predicted in 1920 that some neutral particle having mass equal to that of proton must be present in an atom. He proved in his experiment that nucleus is an extremely small positively charged part. It is situated at the center of an atom it carries nearly the whole mass of an atom.
Q 37. How was it shown that atomic nuclei are positively charged?
Ans: Rutherford observed in his experiment, that the deflection of a few particles proved that there is a center of positive charges in an atom, which is called nucleus of an atom.
Q 38. Name the particle which determine the mass of an atom.
Ans: Proton and neutron are the particles which determine the mass of an atom. These are also known as nucleons.
Q 39. What is the classical theory of radiation? How does it differ from quantum theory?
Ans: Classical theory: According to classical theory, electrons being the charged particles should release or emit energy continuously and they should ultimately fall into the nucleus. Quantum theory: Quantum means fixed energy. It is the smallest. amount of energy that can be emitted or absorbed as electromagnetic radiation.
Q 40. Do you know any element having no neutrons in its atoms.
Ans: Yes, the isotope of hydrogen (Protium) has no neutron.
Q 41. Who discovered an electron, proton and neutron? 1 neutron?
Ans: In 1886, Goldstein discovered positively charged particles called protons. In 1897, J.J. Thomson found in an atom, the negatively charged particles known as electrons. In 1932 Chadwick discovered neutron.
Q 42. How does electron differ from a neutron?
Ans: Electrons: Electron is the negative charge particle. Electron is the revolving around the Nucleus. Neutrons: Neutron is the neutral particle. Neutron is present is the nucleus.
Q 43 Explain how anode rays are formed from the gas taken in the discharge tube.
Ans: Anode rays do not originate from the anode. In fact, these rays are produced when the cathode rays or electrons collide with the residual gas molecules present in the discharge tube and ionize them as follows: M+e^ – M ^ 2 e^ –
Q 44. Why do the isotopes of an element have different atomic masses?
Ans: Because the isotopes of an element have different number of neutrons
Q 45. How many neutrons are present in C-12 and C-13?
Ans: In C-12 there are six neutrons present and in C-13 there are seven neutrons present in the nucleus.
Q 46. Which of the isotopes of hydrogen contains greater number of neutrons?
Ans: Isotopes of hydrogen tritium has greater number of neutrons. It has 2 neutrons.
Q 47. Give one example each of the use of radioactive isotope in medicine and radiotherapy.
Ans: A radioactive isotope used in medicine is lodine-131. Radioactive Isotope used in Radiotherapy is.
Q 48. How is the goiter in thyroid gland detected?
Ans: Isotope of lodine-131 is used for diagnosis of goiter in the thyroid gland.
Q 49. Define nuclear fission reaction.
Ans: Nuclear fission is the type of nuclear reaction in which an. isotopic element is bombarded with slow moving neutrons that isotope of element emits three neutrons and split into same other isotopic elements.
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