Chapter 4 Structure Of The Atom

Question 1. Which of the following correctly represent the electronic distribution in the Mg atom?

(a) 3, 8, 1

(b) 2, 8, 2

(c) 1, 8, 3

(d) 8, 2, 2

Question 2. Rutherford’s ‘alpha ($\alpha$) particles scattering experiment’ resulted in to discovery of

(a) Electron

(b) Proton

(c) Nucleus in the atom

(d) Atomic mass

Question 3. The number of electrons in an element X is 15 and the number of neutrons is 16. Which of the following is the correct representation of the element?

(a) $^{31}_{15}$ X

(b) $^{31}_{16}$ X

(c) $^{16}_{15}$ X

(d) $^{15}_{16}$ X

Question 4. Dalton’s atomic theory successfully explained

(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)

Question 5. Which of the following statements about Rutherford’s model of atom are correct?

(i) considered the nucleus as positively charged

(ii) established that the alpha ($\alpha$) –particles are four times as heavy as a hydrogen atom

(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)

Question 6. Which of the following are true for an element?

(i) Atomic number = number of protons + number of electrons

(ii) Mass number = number of protons + number of neutrons

(iii) Atomic mass = number of protons = number of neutrons

(iv) Atomic number = number of protons = number of electrons

(a) (i) and (ii)

(b) (i) and (iii)

(c) (ii) and (iii)

(d) (ii) and (iv)

Question 7. In the Thomson’s model of atom, which of the following statments are correct?

(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)

Question 8. Rutherford’s alpha ($\alpha$) –particle scattering experiment showed that

(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)

Question 9. The ion of an element has 3 positive charges. Mass number of the atom is 27 and the number of neutrons is 14. What is the number of electrons in the ion?

(a) 13

(b) 10

(c) 14

(d) 16

Question 10. Identify the Mg$^{2+}$ ion from the Fig.4.1 where, n and p represent the number of neutrons and protons respectively

(a) (a)

(b) (b)

(c) (c)

(d) (d)

Question 11. In a sample of ethyl ethanoate (CH$_3$COOC$_2$H$_5$) the two oxygen atoms have the same number of electrons but different number of neutrons. Which of the following is the correct reason for it?

(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.

Question 12. Elements with valency 1 are

(a) always metals

(b) always metalloids

(c) either metals or non-metals

(d) always non-metals

Question 13. The first model of an atom was given by

(a) N. Bohr

(b) E. Goldstein

(c) Rutherford

(d) J.J. Thomson

Question 14. An atom with 3 protons and 4 neutrons will have a valency of

(a) 3

(b) 7

(c) 1

(d) 4

Question 15. The electron distribution in an aluminium atom is

(a) 2, 8, 3

(b) 2, 8, 2

(c) 8, 2, 3

(d) 2, 3, 8

Question 16. Which of the following in Fig. 4.2 do not represent Bohr’s model of an atom correctly?

(i)

(ii)

(iii)

(iv)

(a) (i) and (ii)

(b) (ii) and (iii)

(c) (ii) and (iv)

(d) (i) and (iv)

Question 17. Which of the following statement is always correct?

(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.

Question 18. Atomic models have been improved over the years. Arrange the following atomic models in the order of their chronological order

(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)

Question 19. Is it possible for the atom of an element to have one electron, one proton and no neutron. If so, name the element.

Question 20. Write any two observations which support the fact that atoms are divisible.

Question 21. Will $^{35}$Cl and $^{37}$Cl have different valencies? Justify your answer.

Question 22. Why did Rutherford select a gold foil in his alpha ($\alpha$) –ray scattering experiment?

Question 23. Find out the valency of the atoms represented by the Fig. 4.3 (a) and (b).

(a)

(b)

Question 24. One electron is present in the outer most shell of the atom of an element X. What would be the nature and value of charge on the ion formed if this electron is removed from the outer most shell?

Question 25. Write down the electron distribution of chlorine atom. How many electrons are there in the L shell? (Atomic number of chlorine is 17).

Question 26. In the atom of an element X, 6 electrons are present in the outermost shell. If it acquires noble gas configuration by accepting requisite number of electrons, then what would be the charge on the ion so formed?

Question 27. What information do you get from the Fig. 4.4 about the atomic number, mass number and valency of atoms X, Y and Z? Give your answer in a tabular form.

(X)

(Y)

(Z)

Table 4.1

Question 28. In response to a question, a student stated that in an atom, the number of protons is greater than the number of neutrons, which in turn is greater than the number of electrons. Do you agree with the statement? Justify your answer.

Question 29. Calculate the number of neutrons present in the nucleus of an element X which is represented as $^{31}_{15}$ X

Question 30. Match the names of the Scientists given in column A with their contributions towards the understanding of the atomic structure as given in column B

Question 31. The atomic number of calcium and argon are 20 and 18 respectively, but the mass number of both these elements is 40. What is the name given to such a pair of elements?

Question 32. Complete the Table 4.1 on the basis of information available in the symbols given below

(a) $^{35}_{17}$ Cl

(b) $^{12}_{6}$ C

(c) $^{81}_{35}$ Br

Table 4.1

Question 33. Helium atom has 2 electrons in its valence shell but its valency is not 2, Explain.

Question 34. Fill in the blanks in the following statements

(a) Rutherford’s alpha ($\alpha$) -particle scattering experiment led to the discovery of the ———

(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 ———.

Question 35. An element X has a mass number 4 and atomic number 2. Write the valency of this element?

Question 36. Why do Helium, Neon and Argon have a zero valency?

Question 37. The ratio of the radii of hydrogen atom and its nucleus is $\sim 10^5$. Assuming the atom and the nucleus to be spherical, (i) what will be the ratio of their sizes? (ii) If atom is represented by planet earth ‘Re’ = $6.4 \times 10^6$ m, estimate the size of the nucleus.

Question 38. Enlist the conclusions drawn by Rutherford from his alpha ($\alpha$) -ray scattering experiment.

Question 39. In what way is the Rutherford’s atomic model different from that of Thomson’s atomic model?

Question 40. What were the drawbacks of Rutherford’s model of an atom?

Question 41. What are the postulates of Bohr’s model of an atom?

Question 42. Show diagramatically the electron distributions in a sodium atom and a sodium ion and also give their atomic number.

Question 43. In the Gold foil experiment of Geiger and Marsden, that paved the way for Rutherford’s model of an atom, $\sim$ 1.00% of the alpha ($\alpha$) -particles were found to deflect at angles > 50º. If one mole of alpha ($\alpha$) -particles were bombarded on the gold foil, compute the number of alpha ($\alpha$) -particles that would deflect at angles less than 50º.