Structure of the atom
Multiple Choice Questions
1. Which of the following correctly represent the electronic distribution in the
(a) 3, 8, 1
(b) 2, 8, 2
(c)
(d) 8, 2, 2
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Answer
Answer is 2, 8, 2
Explanation
Atomic number of
(a) Electron
(b) Proton
(c) Nucleus in the atom
(d) Atomic mass
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Answer
Answer is (c) Nucleus in the atom
Explanation:
Rutherford’s ‘alpha
(a)
(b)
(c)
(d)
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Answer
Answer is (a)
Explanation:
Number of protons in an element depicts atomic number. Number of protons and electrons are equal in an element. Hence atomic number is written in subscript whereas mass number is written in the subscript b\times \times \timesore the symbol of the element.
(i) Law of conservation of mass
(ii) Law of constant composition
(iii) Law of radioactivity
(iv) Law of multiple proportion
(a) (i), (ii) and (iii)
(b) (i), (iii) and (iv)
(c) (ii), (iii) and (iv)
(d) (i), (ii) and (iv)
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Answer
Answer is (d) (i), (ii) and (iv)
Explanation:
Dalton’s theory explains Law of conservation of mass, Law of constant composition, Law of multiple proportion. But it never give any details of Law of radioactivity .
(i) considered the nucleus as positively charged
(ii) established that the
(iii) can be compared to solar system
(iv) was in agreement with Thomson’s model
(a) (i) and (iii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) only (i)
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Answer
Answer is (a) (i) and (iii)
Explanation:
Positively charged alpha particles were deflected by nucleus. This shows nucleus is positively charged.
Rutherford also postulated that electrons are arranged in an atom around the nucleus like planets arranged around sun.
(i) Atomic number
(ii) Mass number = number of protons + number of neutrons
(iii) Atomic mass
(iv) Atomic number
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (ii) and (iv)
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Answer
Answer is (d) (ii) and (iv)
Explanation:
Atomic number
(i) the mass of the atom is assumed to be uniformaly distributed over the atom
(ii) the positive charge is assumed to be uniformaly distributed over the atom
(iii) the electrons are uniformaly distributed in the positively charged sphere
(iv) the electrons attract each other to stabilise the atom
(a) (i), (ii) and (iii)
(b) (i) and (iii)
(c) (i) and (iv)
(d) (i), (iii) and (iv)
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Answer
Answer is(a) (i), (ii) and (iii)
Explanation:
Thomson proposed that negatively charged electron are stabilised by positively charged protons in the nucleus. Hence option II) the positive charge is assumed to be uniformly distributed over the atom is wrong statement and other statements are part of Thomson’s model of atom.
(i) electrons have negative charge
(ii) the mass and positive charge of the atom is concentrated in the nucleus
(iii) neutron exists in the nucleus
(iv) most of the space in atom is empty Which of the above statements are correct?
(a) (i) and (iii)
(b) (ii) and (iv)
(c) (i) and (iv)
(d) (iii) and (iv
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Answer
Answer is (b) (ii) and (iv)
Explanation:
An atom consists of a positively charged, dense and very small nucleus which have all the protons and neutrons. Positive charge is due to protons, as neutrons have no charge. Here the space is empty because alpha particles pass straight through the gold foil without any deflection.
Thomson explained that electron s have negative charge. Existence of neutron was discovered by Chadwick.
(a) 13
(b) 10
(c) 14
(d) 16
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Answer
Answer is (b) 10
Explanation
Mass number
Number of neutron in the atom
Number of Electrons=Mass number-Number of neutrons=27-14
Number of electrons
Since ions of the element has 3 positive charges number of electron in the ion is 13-3 which equal 10.
Hence the answer is 10
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(a)
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(b)
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(c)
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(d)
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Answer
Answer is d)
Explanation:
Number of protons in
Number of neutrons in
[as mass number of
(a) One of the oxygen atoms has gained electrons
(b) One of the oxygen atoms has gained two neutrons
(c) The two oxygen atoms are isotopes
(d) The two oxygen atoms are isobars.
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Answer
Answer is(c) The two oxygen atoms are isotopes
Explanation
Two Oxygen atoms in
(a) always metals
(b) always metalloids
(c) either metals or non-metals
(d) always non-metals
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Answer
Answer is (c) either metals or non-metals.
Explanation
If element shows positive valency it is a metal and if the element shows negative valency it will be a non-metal.
(a) N. Bohr
(b) E. Goldstein
(c) Rutherford
(d) J.J. Thomson
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Answer
Answer is (d) J.J. Thomson
(a) 3
(b) 7
(c) 1
(d) 4
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Answer
Answer is (c) 1
(a) 2, 8, 3
(b) 2, 8, 2
(c) 8, 2, 3
(d) 2, 3, 8
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Answer
Answer is (a) 2, 8, 3
Explanation
Atomic number of Aluminium is 13, First shell can have maximum of 2 electron and second shell holds a mximum of 8 electrons. Hence option a is right answer.
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(a)
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(b)
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(c)
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(d)
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (ii) and (iv)
(d) (i) and (iv)
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Answer
Answer is ii and iv
Explanation
First shell can have maximum of 2 electron and second shell can have maximum of 8 electron hence ii and iv do not represent Bohr’s model of an atom correctly.
(a) An atom has equal number of electrons and protons.
(b) An atom has equal number of electrons and neutrons.
(c) An atom has equal number of protons and neutrons.
(d) An atom has equal number of electrons, protons and neutrons.
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Answer
Answer is (a) An atom has equal number of electrons and protons.
Explanation
An atom is electrically neutral because the number of protons are always equal to number of electrons. Hence option a) is right.
(i) Rutherford’s atomic model
(ii) Thomson’s atomic model
(iii) Bohr’s atomic model
(a) (i), (ii) and (iii) (b) (ii), (iii) and (i)
(c) (ii), (i) and (iii)
(d) (iii), (ii) and (i)
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Answer
Answer is (c) (ii), (i) and (iii)
Explanation:
Thomson’s atomic model was proposed in the year 1904
Rutherford’s atomic model was proposed in the year 1911
Bohr’s atomic model was proposed in the year 1913
Short Answer Questions
19. Is it possible for the atom of an element to have one electron, one proton and no neutron. If so, name the element.
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Answer
Yes, Hydrogen is the element which is having only 1 proton and 1 electron and no neutron hence there is no repulsive force in the nucleus hence it is stable.
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Answer
- Ionic compounds are formed because of formation of ions that involves transfer of electrons.
- Difference in the number of make isotopes. This shows that atom is formed by different particles such as electrons, protons and neutrons and element is divisible.
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Answer
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Answer
Rutherford used gold for his scattering experiment because gold is the most malleable metal and he wanted the thinnest layer as possible.
Therefore, Rutherford selected a Gold foil in his alpha scatttering experiment.
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(a)
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(b)
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Answer
Atom (a) has zero valency as it has 8 electron in its valence shell making the configuration stable.
Atom (b) has valency of +1 as it has 7 electrons in it outermost shell . It can accept 1 electron to achieve octet configuration.
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Answer
If an electron is removed from the outermost shell a cation will be formed and the charge of the element will be +1 .
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Answer
Atomic number of chlorine atom
So, its electronic configuration is
K L M
2 8 7
L shell of chlorine contains 8 electrons.
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Answer
In this atom 6 electrons are already present in its outermost orbitals. In order to attain noble gas configuration element has to accept two electron hence its charge is -2 .
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Answer
Atomic number, mass number and valency of atoms X, Y and Z
Atomic no | Mass no | Valency | |
---|---|---|---|
5 | 11 | 3 | |
8 | 18 | 2 | |
15 | 31 | 3.5 |
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Answer
Statement is wrong because number of protons can never be greater than number of neutrons. Number of protons will always be less than or equal to number of neutrons. Number of electrons and protonsare always equal in a neutral atom.
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Answer
Mass number
(A) (B)
(a) Ernest Rutherford - (i) Indivisibility of atoms
(b) J.J.Thomson - (ii) Stationary orbits
(c) Dalton - (iii) Concept of nucleus
(d) Neils Bohr - (iv) Discovery of electrons
(e) James Chadwick - (v) Atomic number
(f) E. Goldstein - (vi) Neutron
(g) Mosley - (vii) Canal rays
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Answer
(A) - (B)
(a) Ernest Rutherford - (iii) Concept of nucleus
(b) J.J.Thomson - (iv) Discovery of electrons
(c) Dalton - (i) Indivisibility of atoms
(d) Neils Bohr - (ii) Stationary orbits
(e) James Chadwick - (vi) Neutron
(f) E. Goldstein - (vii) Canal rays
(g) Mosley - (v) Atomic number
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Answer
Elements with different atomic numbers but same mass numbers are known as isobars. Calcium and argon are isobars.
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Answer
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Answer
Helium has 2 electrons in its outermost shell thereby completing duplet configuration. Hence it has no valence shell left empty making its valency 0 .
(a) Rutherford’s
(b) Isotopes have same _ _ _ but different _ _ _ .
(c) Neon and chlorine have atomic numbers 10 and 17 respectively. Their valencies will be _ _ _ and _ _ _ respectively.
(d) The electronic configuration of silicon is _ _ _ and that of sulphur is
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Answer
(a) Rutherford’s
(b) Isotopes have same atomic number but different mass number
(c) Neon and chlorine have atomic numbers 10 and 17 respectively. Their valencies will be
(d) The electronic configuration of silicon is 2.8.4 and that of sulphur is 2.8.6
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Answer
Mass number
Atomic number
It has 0 valency and it will not react with any other atom because it has its outer shell filled.
Long Answer Questions
36. Why do Helium, Neon and Argon have a zero valency?
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Answer
Helium has 2 electron in its outermost orbit thus filling shell 1 and forming duplet configuration in valence shell .Neon has 8 electron in their valence orbit hence completing duplet configuration. In the same way Argon and Neon has 8 electron in its outermost shelling completing octet configuration. As these elements have maximum electron in their valence shell thus reach stable electron configuration and they will not take part in any sort of chemical reactions.
(i) What will be the ratio of their sizes?
(ii) If atom is represented by planet earth ’
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Answer
Assuming the atom and the nucleus to be spherical.
(a) Atomic size is represented in terms of atomic radius,
As volume of sphere
Thus, the ratio of volumes
(b)
If atom is represented by planet earth with
Then, volume of atom
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Answer
Rutherford drawn following conclusion from his
-particles passed through the gold foil without any deflection concluding the empty space inside the atom.- Deflection is observed in few particles which proves positive charge of the atom occupies very little space.
- Deflection in A very small fraction of
-particles indicates that all the positive charge and mass of the gold atom were concentrated in a very small volume within the atom.
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Answer
Rutherford proposed that electron revolve around the nucleus in well differentiated orbits. Nucleus is the centre which is positively charged. Rutherford proposed that nucleus is very small and nearly all the mass of an atom is centred in the nucleus.
Thompson proposed that electron are scattered positively charged spheres like a Christmas pudding and the mass of the atom was supposed to be uniformly distributed.
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Answer
Rutherford’s model could not explain the stability of the atom.
Revolving electrons would lose energy as they are the charged particles and due to acceleration, charged particles would radiate energy.
Orbit of the revolving electron will reduce in size, following a spiral path as shown in figure and ultimately the electron should fall into the nucleus. In other words, the atom should collapse.
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Continuous loss of energy by a revolving electron
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Answer
Postulates of Bohr’s model of an atom are
(i) Only certain special orbits known as discrete orbits of electrons, are allowed inside the atom.
(ii) While revolving in discrete orbits the electrons do not radiate energy. These orbits or shells are called energy levels. These orbits or shells are represented by the letters K,L,M,N,… or the numbers,
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Answer
Atomic number of sodium
Number of protons in the nucleus
Number of electrons
Electronic configuration of
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Sodium atom
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Sodium ion
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Answer
Total number of
1 mole
number of
Number of
Actual number of