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Science One word answer.

Structure of the Atom · Gujarat Board (GSEB) STD 9 (GSEB - English Medium). 112 questions.

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Question 11 Mark
If K and L shells of an atom are full, then what would be the total number of electrons in the atom?
Answer
K shell can hold 2 electrons and L shell can hold 8 electrons. When both the shells are full, there will be (8 + 2) 10 electrons in the atom.
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Question 21 Mark
Name the three sub-atomic particles of an atom.
Answer
The three sub-atomic particles of an atom are:
  1. Protons.
  2. Electrons.
  3. Neutrons.
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Question 41 Mark
On the basis of Rutherford’s model of an atom, which subatomic particle is present in the nucleus of an atom?
Answer
On the basis of Rutherford’s model of an atom, protons (positively-charged particles) are present in the nucleus of an atom.
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Question 51 Mark
What are canal rays?
Answer
Canal rays are positively charged radiations. These rays consist of positively charged particles known as protons. They were discovered by Goldstein in 1886.
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Question 61 Mark
Put tick $(\checkmark)$ against correct choice and cross $(\times)$ against wrong choice.
Number of valence electrons in Cl– ion are:
  1. 16
  2. 8
  3. 17
  4. 18
Answer
Number of valence electrons in Cl-ion are:
  1. 16 $(\times)$
  2. 8 $(\checkmark)$
  3. 17 $(\times)$
  4. 18 $(\times)$
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Question 71 Mark
Put tick $(\checkmark)$ against correct choice and cross $(\times)$ against wrong choice.
Isotopes of an element have
  1. The same physical properties.
  2. Different chemical properties.
  3. Different number of neutrons.
  4. Different atomic numbers.
Answer
Isotopes of an element have
  1. The same physical properties $(\times)$
  2. different chemical properties $(\times)$
  3. different number of neutrons $(\checkmark)$
  4. different atomic numbers $(\times)$
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Question 81 Mark
Put tick $(\checkmark)$ against correct choice and cross $(\times)$ against wrong choice.
Rutherford’s alpha-particle scattering experiment was responsible for the discovery of
  1. Atomic Nucleus.
  2. Electron.
  3. Proton.
  4. Neutron.
Answer
Rutherford’s alpha-particle scattering experiment was responsible for the discovery of
  1. Atomic nucleus $(\checkmark)$
  2. Electron $(\times)$
  3. Proton $(\times)$
  4. Neutron $(\times)$
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Question 91 Mark
Name the discoveror of electrons, protons and neutrons.
Answer
Neutron: The neutron was discovered in 1932 by the English physicist James Chadwick.
Proton: Goldstein in 1886
Electron: J.J Thomson n in 1897
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Question 101 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 111 Mark
Is it possible for the atom of an element to have one electron, one proton and no neutron. If so, name the element.
Answer
Yes, it is true for the common, stable isotope of hydrogen (protium) which is represented as $1^{1\text{H}}.$
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Question 121 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 131 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 141 Mark
Name the particles which actually determine the mass of an atom.
Answer
Protons and neutrons actually determine the mass of atom.
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Question 151 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 161 Mark
Name the shell of an atom which can accommodate a maximum of:
  1. 2 electrons.
  2. 18 electrons.
Answer
  1. K shell can accommodate maximum of 2e-
  2. M shell can accommodate maximum of 18e-
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Question 171 Mark
Given that the percentage abundance of the isotope is 90% and that of the isotope is 10%, calculate the average atomic mass of neon.
Answer
$\text{Atomicmass}=\sum\text{Mass no.}\times\%\text{ of that isotope}$
$\text{Atomicmass}=20\times\frac{90}{100}+2\times\frac{10}{100}$
$\text{Atomicmass}=20.2\text{u}$
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Question 191 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 201 Mark
How are the following pairs of atoms related?
$ _8\text{X}^{16},\ _8\text{X}^{17},\ _{18}\text{Y}^{40},\ _{20}\text{Z}^{40}$
Answer
Elements $_8\text{X}^{16}$ and $_8\text{X}^{17}$ are isotopes because of a same number of protons.

Elements $_{18}\text{Y} ^{40}$ and $_{20}\text{Z}^{40}$ are isobars because of the same mass number.

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Question 211 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 221 Mark
Rutherford's $\alpha-$ particle scattering experiment led to the discovery of:
  1. Electrons
  2. Protons
  3. Neutrons
  4. Atomic nucleus
Answer
  1. Atomic nucleus
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Question 231 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 251 Mark
State the number of electrons present in the outermost shell of the atom of the following elements:
  1. Neon.
  2. Chlorine.
Answer
  1. 8 electrons are present in outermost shell of Neon.
  2. 7 electrons are present in outermost shell of Chlorine.
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Question 261 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 271 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 281 Mark
State one use of radioactive isotopes in medicine.
Answer
Radioactive isotopes are used in the treatment of cancer.
One such isotope is Cobalt-60.
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Question 291 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 301 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 311 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 321 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 331 Mark
Name two disease transmitted by the contaminated food and water.
Answer
Cholera and Hepatitis A are transmitted by the contaminated food and water.
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Question 341 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 351 Mark
If an atom of an element has atomic number = 15 and, mass number = 31, find the number of protons, electrons, neutrons in its atoms.
Answer
This is the isotope phosphorus - 31. It has 15 protons, 15 electrons, and 16 neutrons.

Explanation:

The atomic number for any element is the number of protons in its atomic nuclei. In a neutral atom, the number of electrons are the same as the number of protons. The atomic mass (mass number) is the sum of the protons and neutrons in the nucleus. Mass number can vary due to the fact that the number of neutrons can vary. Isotopes are named for their mass numbers.

So, this element has 15 protons (atomic number), 15 electrons, and 16 neutrons (mass number minus atomic number).

This isotope is phosphorus-31, which has atomic number 15.

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Question 361 Mark
Name the central part of an atom where protons and neutrons are held together.
Answer
Nucleus is the central part of an atom in which protons and neutrons are held together.
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Question 371 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 381 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 391 Mark
Explain why, the atomic masses of many elements are in fractions and not whole numbers.
Answer
The fractional atomic masses of elements are due to the existence of their isotopes having different masses.
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Question 401 Mark
Name the gas which produces anode rays consisting of protons in the discharge tube experiment.
Answer
Hydrogen gas produces anode rays consisting of protons in the discharge tube experiment.
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Question 411 Mark
The atomic number of an element X is 16.
Write down the electronic configuration of X.
Answer
Atomic No. of X = 16
E.C. of X = (2, 8, 6)
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Question 421 Mark
All the gases form cathode rays and anode rays when electricity is passed through them:
What does the formation of cathode rays tell us about the atoms?
Answer
Formation of cathode rays tells about the presence of negatively charged electrons in all the atoms.
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Question 431 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 441 Mark
For the symbols H, D and T, write the subatomic particles (protons, neutrons and electrons) found in each one of them.
Answer
H–1 proton, 1 electron and no neutron.
D–1 proton, 1 electron and 1 neutron.
T–1 proton, 1 electron and 2 neutrons.
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Question 461 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 471 Mark
An element X has 5 electrons in its M-shell. What is its atomic number?
Answer
If the element has 5 electrons in the M shell, it is in the 3rd period of Periodic Table and 15th group. 
The element in 3rd period and 15th group is Phosphorous. 
Hence "X" is Phosphorous (P).
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Question 481 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 491 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 501 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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