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Science Do as directed; [Che-1 M]

Structure of the Atom · CBSE STD 9 (CBSE - English Medium). 112 questions.

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Question 11 Mark
Write the name of the sub-atomic particle discovered by J. Chadwick. What type of charge occurs on this particle? In which part of an atom this particle is located? 
Answer
Chadwick discovered neutron. Neutron is a neutral particle so it does not have any charge. It is located in nucleus of any atom. 
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Question 21 Mark
Write the electronic configuration of the element with atomic number 17. Indicate the valency of the element.
Answer
Atomic No. = 17
E.C. = (2, 8, 7)
Valency = 8 - no. of valence electrons
Valency = 8 - 7
Valency = 1
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Question 31 Mark
Write the distribution of electrons in an atom of element whose atomic number is 18. What is special about the outermost electron shell (or valence shell) of the atom of this element?
Answer
Atomic No: 18
Electronic configuration: (2, 8, 8)
The special thing about the outermost shell is that it is completely filled with the electrons.
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Question 41 Mark
Write one pair of isobars.
Answer
isobars are the atoms of different element which have same mass number bit different atomic number. eg- $^{40}\text{Ar}_{18}$ and $^{40}\text{Ar}_{19}.$ Since isobars compounds have same mass number but different atomic number and chemical properties depend upon no. of electrons so isobars have different chemical properties.
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Question 51 Mark
Write down the electron distribution of chlorine atom. How many electrons are there in the L shell? (Atomic number of chlorine is 17).
Answer
Since the atomic number (Z) of chlorine is 17, the electronic configuration of chlorine will be 2, 8, 7. There are eight electrons in the L shell (second shell).
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Question 61 Mark
Why is Thomson’s model of an atom compared with watermelon? 
Answer
Thomson’s model an atom can be considered as a watermelon in which red fleshy part represents positive charge whereas electrons (negative charge) are embedded in it similar to seeds. 
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Question 71 Mark
Why do isotopes have different mass numbers?
Answer
Isotopes of any element have the same number of protons but different in neutron number, therefore, they have different mass numbers .
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Question 81 Mark
Who discovered the neutron?
Answer
It is remarkable that the neutron was not discovered until 1932 when James Chadwick used scattering data to calculate the mass of this neutral particle. Since the time of Rutherford it had been known that the atomic mass number A of nuclei is a bit more than twice the atomic number Z for most atoms and that essentially all the mass of the atom is concentrated in the relatively tiny nucleus.
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Question 101 Mark
Which subatomic particle whose relative charge is:
  1. Chadwick?
  2. Thomson?
  3. Goldstein?
Answer
  1. Chadwick discovered ‘neutron’.
  2. Thomson discovered ‘electron’.
  3. Goldstein discovered ‘proton’.
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Question 111 Mark
Which subatomic particle is not present in an ordinary hydrogen atom?
Answer
Neutron is not present in ordinary hydrogen atom.
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Question 121 Mark
Which shell of an atom can accommodate a maximum of:
  1. 8 electrons?
  2. 32 electrons?
Answer
  1. L shell can accommodate maximum of 8e-
  2. N shell can accommodate maximum of 32e-
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Question 131 Mark
Which scientist concluded that the size of the nucleus is very small as compared to the size of an atom?
Answer
Rutherford concluded that size of nucleus is very small as compared to size of an atom.
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Question 141 Mark
Which radioactive isotope is used to determine the activity of thyroid gland?
Answer
lodine-131 radioisotope is used to determine the activity of thyroid gland.
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Question 151 Mark
Which part of an atom was discovered by Rutherford’s alpha particle scattering experiment?
Answer
Nucleus was discovered by Rutherford in the alpha particle scattering experiment.
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Question 161 Mark
Which of the nuclear particles is present in the same fixed number in the atoms of any particular element?
Answer
Proton is present in same fixed no. in the atoms of any particular element.
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Question 171 Mark
Which of the following are isotopes and which are isobars?
Argon, Deuterium, Calcium, Tritium, Protium.
Answer
Deuterium, Protium and Tritium are isotopes.
Argon and Calcium are isobars.
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Question 181 Mark
Which noble gas has less than 8 electrons in the valence shell of its atom? What is this number?
Answer
Helium has less than 8 electrons in the valence shell of an atom. Its atomic no. is 2
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Question 191 Mark
What name is given to those isotopes which have unstable nuclei and emit various types of radiations?
Answer
Radioactive isotopes have unstable nuclei and emit various types of radiations.
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Question 201 Mark
What name is given to those atoms which contain the same number of protons and electrons but different number of neutrons?
Answer
Atoms containing same number of protons and electrons but different number of neutrons are called ISOTOPES.
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Question 211 Mark
What name is given to the pair of atoms such as $^{14}_\text{ 7}\text{N}\ \text{and }^{15}_\text{ 7}?$
Answer
The given pair are isotopes.
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Question 231 Mark
What is the similarity in the electronic structure of the following set of atoms?
  1. Lithium.
  2. Sodium.
  3. Potassium.
Answer
  1. Li: 2, 1 
  2. Na: 2, 8, 1
  3. K: 2, 8, 8, 1

Clearly, all of these have one electrons each in their outermost shells.

The main points of similarity are:

  • They all have an unpaired electron in an s orbital.
  • They all have an unpaired electron with a magnetic quantum number, ml = 0.
  • They all have an unpaired electron with an angular momentum quantum number, l = 0.
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Question 241 Mark
What is the relationship between an atom containing 11 protons, 11 electrons ad 11 neutrons, and another atom containing 11 protons, 11 electrons and 12 neurtrons?
Answer
Isotopes.
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Question 251 Mark
What is the relation between the atomic number and mass number of an element?
Answer
Mass No. = Atomic no. + No. of neutrons
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Question 261 Mark
What is the reason for the slightly different physical properties of all the isotopes of an element?
Answer
Due to slight difference in the masses of the isotopes of an element, the physical properties of the isotopes are slightly different.
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Question 271 Mark
What is the reason for the identical chemical properties of all the isotopes of an element? Explain with the help of an example.
Answer
Because all the isotopes of an element have identical atomic configuration containing same number of valence electrons, therefore, all the isotopes of an element show identical chemical properties.
For example: Cl-35 and Cl-37, show identical chemical properties as they have same no. of 7 valence electrons.
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Question 281 Mark
What is the reason for the different atomic masses of the isotopes of an element?
Answer
The difference in the masses of isotopes of an element is due to different number of neutrons in their nuclei.
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Question 291 Mark
What is the positive charge on the nucleus of an atom due to?
Answer
Positive charge on the nucleus is due to presence of protons.
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Question 301 Mark
What is the number of valence electrons in the chlorine atom?
Answer
Chlorine has 7 valence electrons.
Explanation: You know this by looking at the groups (vertical) of the periodic table. Chlorine is in the Halogens (Group 17) so it has a - 1 charge (meaning 7 valence electrons; one short of 8, which makes a full octet)
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Question 311 Mark
What is the number of valence electrons in the atoms of an element having atomic number 13? Name the valence shell of this atom.
Answer
There are 3 valence electrons present in the element with atomic no. 13.
Valence shell of this atom is M.
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Question 321 Mark
What is the number of sub-atomic particles in this isotope?
Answer
Sub particles in Uranium - 235 are:
Protons = 92
Neutrons = 143
Electrons = 92
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Question 331 Mark
What is the nucleus of an atom and what is the nature of charge on it?
Answer
Nucleus is a small positively charged part at the center of an atom. Nucleus is positively charged.
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Question 341 Mark
What is the maximum number of electrons which can be accommodated in the:
Outermost shell of an atom?
Answer
Maximum of 8e- can be accommodated in outermost shell of an atom.
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Question 351 Mark
What is the maximum number of electrons which can be accommodated in the:
Innermost shell of an atom?
Answer
Maximum of 2e- can be accommodated in innermost shell of an atom.
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Question 361 Mark
What is the maximum number of electrons which can be accommodated in the L shell of an atom?
Answer
Maximum of 8e- can be accommodated in L shell of an atom.
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Question 371 Mark
What is the maximum number of electrons that can go into the N shell of an atom?
Answer
Maximum of 32e- can be accommodated in N shell of an atom.
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Question 381 Mark
What is the maximum number of electrons an M shell of the atom can accommodate?
Answer
Maximum of 18e- can be accommodated in M shell of an atom.
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Question 391 Mark
What is the general name of the elements having 8 electrons in the valence shell of their atoms?
Answer
Noble gases.
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Question 411 Mark
What is the absolute mass and charge of a proton?
Answer
Absolute mass of proton 1.6 × 10-27Kg
Absolute charge of proton 1.6 × 10-19C
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Question 421 Mark
What is the absolute mass and charge of an electron?
Answer
Absolute mass of electron is 9 × 10-28Kg
Absolute charge on electron is 1.6 × 10-19C
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Question 431 Mark
What is a proton? How does it differ from a neutron?
Answer
Protons are positively charged particle found in the atoms of all the elements whereas neutron is a neutral particle found in the nucleus of an atom.
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Question 441 Mark
What is a neutron? State its relative mass and charge.
Answer
The neutron is a neutral particle found in the nucleus of an atom. Its relative mass is 1u. It has no charge.
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Question 451 Mark
What do you understand by the term ‘discrete orbit’?
Answer
The path or orbit of electrons in which they move is called discrete path or discrete orbit.
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Question 461 Mark
What do we call this number which is characteristic of a particular element?
Answer
Atomic no. is characteristic for any particular element.
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Question 471 Mark
What conclusion is obtained from the fact that all the gases form cathode rays?
Answer
The conclusion is that all the atoms contain negatively charged particles called electrons.
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Question 481 Mark
What can be the maximum number of electrons in the outermost orbit?
Answer
Eight
The outermost shell in an atom cannot have more than eight electrons even if it has a capacity to take up more electrons. This is also called the octet rule.
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Question 491 Mark
What are valence electrons? Where are valence electrons situated in an atom?
Answer
The number of electrons present in the valence shell are called valence electrons.
Valence electrons are situated in the outermost shell.
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Question 501 Mark
What are the various letters used by Bohr to represent electron shells in an atom?
Answer
K, L, M, N were the letters used by Bohr to represent electron shells in an atom.
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