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Structure Of The Atom Class 9 Science Assignment Pdf
Class 9 Science students should refer to the following printable assignment in Pdf for Structure Of The Atom in standard 9. This test paper with questions and answers for Grade 9 Science will be very useful for exams and help you to score good marks
Class 9 Science Assignment for Structure Of The Atom
Structure of the Atom
Q 1 Write the electronic configuration of chlorine.
Q 2 What determines the chemical nature of an element?
Q 3 What do you mean by atomic number of an element?
Q 4 Define cathode rays.
Q 5 Which elements have tendency to gain electrons?
Q 6 What is the relation between mass number and atomic number?
Q 7 Name the radioisotopes used to –
(a) determine the activity of thyroid gland.
(b) detect blood cells.
Q 8 What do you understand by isobars?
Q 9 What is the general name of the elements having 2 or 8 electrons in the valence shell of their atoms?
Q 10 Explain the two types of valency.
Q 11 Name three subatomic particles present in an atom.
Q 12 Who discovered neutron?
Q 13 Name the scientist who proposed that the atoms are indivisible?
Q 14 Name the scientist who presented the model of the structure of an atom for the first time.
4. Structure of the Atom
Q 1 What are canal rays?
Q 2 If an atom contains one electron and one proton, will it carry any charge or not?
Q 3 On the basis of Thomson‘s model of an atom, explain how the atom is neutral as a whole?
Q 4 What do you think would be the observation if the alpha-particle scattering experiment is carried out using a foil of a metal other than gold?
Q 5 Helium atom has an atomic mass of 4 unit and 2 protons in its nucleus. How many neutronsare present in its nucleus?
Q 6 Find the valency of chlorine, magnesium, and sulphur.
Q 7 What is the mass and charge of an electron ?
Q 8 Describe the structure of atom as explained by J.J Thomson.
Q 9 Define the term atomic number.
Q 10 Define the mass number of an element.
Q 11 Name the scientists who discovered
(a) Nucleus of atom
Q 12 Name the particles which are present in the nucleus and what type of charge is there on them?
Q 13 Define cathode rays.
Q 14 Write the relation between mass number and atomic number.
Exam Questions NCERT Class 9 Science Chapter 4 Structure of the Atom
Question. Give the number of electron, proton and neutron in 59CO27 and 108Ag47.
(i) Number of protons in Co = 27
(ii) Number of electrons in Co = 27
(iii) Number of neutrons in Co = 59 – 27 = 32
(iv) Number of protons in Ag = 47
(v) Number of electrons in Ag = 47
(vi) Number of neutrons in Ag = 108 – 47 = 61
Question. Do isotopes of an element have similar chemical properties?
Ans : Isotopes of an element have similar chemical properties because they have the same atomic number and valence electrons.
Question. Are noble gases inert?
Ans : The outermost shell of the atoms of noble gases are completely filled. So, they do not show affinity towards chemical reactions.
Question. What are valence electrons?
Ans : The electrons present in the outermost shell of an atom are known as valence electrons.
Question. Give two uses of isotopes in the field of medicines.
Ans : (i) An isotope of cobalt is used in the treatment of cancer.
(ii) An isotope of iodine is used in the treatment of goitre.
Question. What is meant by electronic configuration of elements?
Ans : The systematic distribution of electrons in various orbits of an atom is called electronic configuration of elements.
Question. Define atomic number. How it is denoted?
Ans : Number of protons of an atom determines its atomic number. It is denoted by ‘Z’.
Question. Why helium have zero valency?
Ans : Helium have zero valency because its outermost orbit is completely filled.
Question. Give the derivative source of sodium.
Ans : The symbol of Na for sodium is derived from its Latin name ‘Natrium’.
Question. Give drawbacks of Rutherford’s model.
Ans : Drawbacks of Rutherford’s model :
(i) Unable to explain the source of energy required for movement of electrons.
(ii) Unable to explain as to why a moving charge does not lose energy and fall into the nucleus.
(iii) It could not explain about the emission of radiations of different frequencies by different atoms when heated.
(iv) It could not explain the stability of an atom when charged electrons are moving under the attractive force of positively charged nucleus.
Question. Helium atom has an atomic mass of 4u and two protons in its nucleus. How many neutrons it have?
Ans : Mass number = Number of protons + Number of neutrons
4 =2 + No. of neutrons Number of neutrons = 4 – 2 = 2
Question. How can an atom become stable by losing or gaining electrons?
Ans : For stability of an atom it must have either 2 or 8 electrons in the outermost orbit. So, by losing or gaining electrons it reaches to the electronic configuration of the nearest noble gas.
Question. Give important properties of cathode rays.
Ans : (i) Cathode rays travel in straight line.
(ii) Cathode rays can rotate a light wheel placed in their path.
(iii) They ionise gas through which they pass.
(iv) They are deflected by magnetic field.
(v) They can penetrate through thin metallic sheet.
(vi) Mass of cathode ray particle is too small.
Question. How does an atom become a cation?
Ans : When an atom acquires positive charge by losing one or more electrons, it is called cation.
Question. How are the canal rays different from electrons in terms of charge and mass?
Ans : Electrons are negatively charged particles, mass of which is approximately 2000 1 that of canal rays.
Question. Write any two observations which support the fact that atoms are divisible.
Ans : Discovery of electrons and protons are two observations which support the fact that atoms are divisible.
Question. If an atom contains one electron and one proton, will it carry any charge or not?
Ans : It will not carry any charge because the positive charge on the proton neutralizes the negative charge on the electron.
Question. How has atomic number improved the definition of an element?
Ans : (i) Atomic number of an element = number of proton
= number of electron
(ii) Atomic number gives the position of the element in periodic table. An element can now be defined as a substance comprising of atoms all of which have same atomic number.
Question. Can the addition of neutron to the nucleus of an atom determine the atomic mass or number?
Ans : It will increase the atomic mass of the atom.
Question. What is an anion?
Ans : When an atom gains one or more electrons, it becomes negatively charged and is known as anion.
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