Structure Of The Atom   

Q1. Elements with valency 1 are

(a) always metals

(b) always metalloids

(c) either metals or non-metals

(d) always non-metals.

Ans. (c) either metals or non-metals

Q2. The first model of an atom was given by

(a) N. Bohr

(b) E. Goldstein

(c) Rutherford

(d) J.J. Thomson

Ans. (d) J.J. Thomson

Q3. Rutherford’s alpha-particle scattering experiment was responsible for the discovery of

(a) Atomic Nucleus (b) Electron

(c) Proton              (d) Neutron

Ans. (a) Atomic Nucleus

Q4. Isotopes of an element have

(a) the same physical properties

(b) different chemical properties

(c) different number of neutrons

(d) different atomic numbers.

Ans. (c) different number of neutrons

Q5. 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 number = 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)

Ans. (d) (ii) and (iv)

Q6. 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)

Ans. (c) (ii), (i) and (iii)

Q7. Is it possible for the atom of an element to have one electron, one proton and no neutron? If so, name the element.

Ans. Yes, hydrogen has one electron, one proton and no neutron.

Q8. If bromine atom is available in the form of, say, two isotopes , calculate the average atomic mass of bromine atom.

Ans. Average atomic mass = (79 x 49.7/100) + (81 x 50.3/100)

                                       = 80.006 u

Q9. The electron distribution in an aluminium atom is

(a) 2,8,3

(b) 2,8,2

(c) 8,2,3

(d) 2,3,8

Ans. (a) 2,8,3

Aluminium has 13 electrons. Its electron distribution is 2, 8, 3.

Q10. 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?

Ans. Atoms having the same mass number but different atomic numbers are called isobars.

Q11. Name the three sub-atomic particles of an atom.

Ans. The three sub-atomic particles of an atom are: (i) electrons, (ii) protons and (iii) neutrons.

Q12. 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?

Ans. When an atom has 6 electrons in its outermost shell and it accepts 2 electrons, it gets two negative charges.

Q13. Why did Rutherford select a gold foil in his α-ray scattering experiment?

Ans. He selected a gold foil because he wanted as thin a layer as possible. This gold foil was about 1000 atoms thick.

Q14. If Z = 3, what would be the valency of the element? Also, name the element.

Ans. The electronic configuration of (Z) = 2, 1. Thus, outermost shell has 1 electron. So, its valency = 1. Name of the element is lithium.

Q15. On the basis of Rutherford’s model of an atom, which subatomic particle is present in the nucleus of an atom?

Ans. Proton, a positively charged sub-atomic particle is present in the nucleus of an atom according to Rutherford’s model of atom.

Q16. One electron is present in the outermost 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 outermost shell?

Ans. If this electron is removed from the outermost shell, a cation (positive ion) will be formed with a charge of + 1.

Q17. Which one of the following is a correct electronic configuration of sodium?

(a) 2,8 (b) 8,2,1 (c) 2,1,8 (d) 2,8,1.

Ans. (d) 2, 8, 1

Explanation: Atomic number of sodium (Na) = 11

Electronic configuration = 2, 8, 1

Q18. 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

Ans. (b) 2, 8, 2

Atomic number of Mg = 12. Therefore, electronic distribution will be 

K-2, L-8, M-2

Q19. An atom with 3 protons and 4 neutrons will have a valency of

(a) 3     (b) 7      (c) 1     (d) 4

Ans. (c) 1     

Neutrons = 4, protons = 3, hence electrons = 3 

Distribution of electrons = 2, 1

As, it has one valence electron, therefore its valency is 1.

Q20. 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.

Ans. (a) An atom has equal number of electrons and protons.

Atoms are electrically neutral as number of protons and electrons are equal.

Q21. Calculate the number of neutrons present in the nucleus of an element  which is represented . 

Ans. Atomic number = 15

Mass number = 31

Number of neutrons = 31-15=16

Q22. Rutherford’s alpha (α) particles scattering experiment resulted into discovery of

(a) electron  (b) proton  (c) nucleus in the atom  (d) atomic mass

Ans. (c) nucleus in the atom

Rutherford’s alpha-particle scattering experiment led to the discovery of the atomic nucleus.

Q23. If an atom contains one electron and one proton, will it carry any charge or not?

Ans. No, the atom will not carry any charge. Electron has one negative charge (-1) and the proton has one positive charge (+1). Thus, they neutralize each other.

Q24. What do you think would be the observation if the α-particle scattering experiment is carried out using a foil of a metal other than gold?

Ans. On using foil of any metal, the observations of the α-particle scattering experiment would remain the same. This is because the structure of atom when considered individually remains the same.

Q25. 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).

Ans. (d) Dalton’s atomic theory successfully explained law of conservation of mass, law of constant composition and law of multiple proportion. But it never gives any details of Law of radioactivity.

Q26. Complete the table on the basis of information available in the symbols given below.

Ans.