4 : STRUCTURE OF THE ATOM

Class 9 Science Examplar Chapter 4 : STRUCTURE OF THE ATOM

Chapter 4. Structure of the Atom

Class 9 Science Examplar Chapter 4 : STRUCTURE OF THE ATOM Choose the correct Answers :

Q1. Rutherford’s alpha-particle scattering experiment was responsible for the discovery of :

(A) Atomic Nucleus

(B) Electron

(D) Neutron

Ans : (A) Atomic Nucleus

Q2. Isotopes of an element have

(A) the same physical properties .

(B) different chemical properties .

(D) different atomic numbers .

Ans : (C) different number of neutrons

Q3. The number of valence electrons in ion are :

(A) 16

(B) 8

(D) 18

Ans : (D) 18

Q4.Which one of the following is a correct electronic configuration of Sodium ?

(A) 2 , 8

(B) 8 , 2 , 1

(D) 2 , 8 , 1

Ans : (D) 2 , 8 , 1

Q5. The maximum number of electrons that can be accommodated in the outermost orbit is :

(A) 2

(B) 8

(D) 32

Ans : (B) 8

Q6. If Z = 3 , what would be the valency of the element ?

(A) 3

(B) 1

(D) 2

Ans : (B) 1

Q7. Electronic Configuration of Magnesium is :

(A) 2 , 8 , 1

(B) 2 , 8 , 2

(D) 2 , 8 , 4

Ans : (B) 2 , 8 , 2

Q8. The number of Neutrons of is :

(A) 13

(B) 27

(D) 40

Ans : (C) 14 [27-13 = 14]

Q9. Isobars of an element have

(A) the same physical properties .

(B) different chemical properties .

(D) same atomic mass but different atomic numbers .

Ans : (D) same atomic mass but different atomic numbers .

Q10. If number of electrons in an atom is 8 and number of protons is also 8 , then the atomic number of the atom is :

(A) 0

(B) 8

(D) 12

Ans : (B) 8 [ Electrons = Protons]

Q11. Which of the following correctly represent the electronic distribution in the Mg atom ?

(A) 3 , 8 , 1

(B) 2 , 8 , 2

(D) 8 , 2 , 2

Ans : (B) 2 , 8 , 2

Q12. 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)

(B)

(C)

(D)

Ans : (A) [Mass = electron + neutron]

Q13. 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)

(D) (i) , (ii) and (iv)

Ans : (D) (i) , (ii) and (iv)

Q14. Which of the following statements about Rutherford’s model of atom are correct ?

(i) considered the nucleus as positively charged .

(ii) established that the - 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)

(D) only (i)

Ans : (A) (i) and (iii)

Q15. 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)

(D) (ii) and (iv)

Ans : (ii) and (iv)

Q16. In the Thomson’s model of atom, which of the following statements are correct ?

(i) the mass of the atom is assumed to be uniformly distributed over the atom .

(ii) the positive charge is assumed to be uniformly distributed over the atom .

(iii) The electrons are uniformly distributed in the positively charged sphere .

(iv) the electrons attract each other to stabilize the atom .

(A) (i) , (ii) and (iii)

(B) (i) and (iii)

(D) (i) , (iii) and (iv)

Ans : (A) (i) , (ii) and (iii)

Q17. Rutherford’s -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)

(D) (iii) and (iv)

Ans : (B) (ii) and (iv)

Q18. The ion od 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

(D) 16

Ans : (B) 10

Q19. Identify the ion from the fig. 4.1 , where , n and p represent the number of neutrons and protons respectively .

(A) (B)

Ans : (B)

Q20.Elements with valency 1 are :

(A) always metals

(B) always metalloids

(D) always non-metals

Ans : (C) either metals or non-metals

Q21. The first model of an atom was given by

(A) N. Bohr

(B) E. Goldstein

(D) J.J. Thomson

Ans : (D) J.J. Thomson

Q22. An atom with 3 protons and 4 neutrons will have a valency of :

(A) 3

(B) 7

(D) 4

Ans : (C) 1 [E.C. of Atom = 2.1]

Q23. The electron distribution in an aluminium atom is :

(A) 2 , 8 , 3

(B) 2 , 8 , 2

(D) 2 , 3 , 8

Ans : (A) 2 , 8 , 3

Q24. 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)

(D) (i) and (iv)

Ans : (C) (ii) and (iv)

Q24. 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 .

(D) An atom has equal number of electrons , protons and neutrons .

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

Q25. 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)

(D) (iii) , (ii) and (i)

Ans : (C) (ii) , (i) and (iii)

Q26. An element X has a mass number 4 and atomic number 2 , then the valency of this element is :

(A) 4

(B) 2

(D) 1

Ans : (B) 2

Class 9 Science Examplar Chapter 4 : STRUCTURE OF THE ATOM Fill in the blanks :

Q27. Rutherford’s -particle scattering experiment led to the discovery of the .

Ans : Nucleus

Q28. Isotopes have same but different .

Ans : Atomic number , mass number .

Q29. Neon and chlorine have atomic numbers 10 and 17 respectively . Their valencies will be and respectively .

Ans : 0 , 1

Q30. The electron configuration of silicon and that of sulphur is .

Ans : 2.8.4 and 2.8.6