WORKSHEET CHAPTER-4. Structure of the Atom

4. Structure of the Atom

I. For question numbers 1 to 8, two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a). (b), (c) and (d) as given below :

 (a) Both A and R are true and R is the correct explanation of the assertion.

(b) Both A and R are true butRis not the correct explanation of the assertion.

 (c) A is true but R is false.

 (d) A Is false but R is true. (1 Mark)

1. Assertion (A) : Electrons, protons and neutral particles (neutrons) in an atom are called 'sub-atomic particles'.

Reason (R) : According to John Dalton's atomic theory, an atom can be further subdivided into three fundamental 'sub-atomic partides'.

2. Assertion (A) : JJ. Thomson explained presence of electrons by cathode rays experiment. Reason (R) : Charge on an electron is equal to - 1.6 x 10"C and mass of the electron is 9.1 x 10 kg.

3. Assertion (A) : E Goldstein through his famous anode rays'canal rays experiment, was able to detect the presence of positively charged particles called protons in the atom.

 Reason (R): The behavior of positively charged particles in the magnetic or electrical field is same as that observed for electrons or cathode rays.

4. Assertion (A) : In Rutherford's 'a-ray scattering experiment, most of the a-particles passed undeflected through the gold foil.

 Reason (R) : It was due to the fact that most of the space in an atom is empty.

5. Assertion (A) : Unstability of an atom was the major drawback of Rutherford's atomic Ppou Reason (R) : According to Rutherford, electrons revolve around the nucleus in well-defined orbits.

 6. Assertion (A) : Neils Bohr in 1912, proposed modified model of an atom to explain its stability that could not be explained by Rutherford's model.

 Reason (R) : Bohr's model states that long as an electron remains in a particular orbit it neither loses nor gains energy.

7. Assertion (A) : a and CI. are the two isotopes of chlorine.

 Reason (R) : Isotopes are atoms of same elements having same atomic number and different mass umbers.

8. Assertion (A) : The first, second and third shell contain 2, 8 and 18 electrons respectively. Reason (R) : The maximum mumber of electrons that can be accommodated in a shell is 2n2.

 

 

11. Question numbers (a - d) are based on the tables given below. Study the table and answer the questions that follow :

Atoms / lons	Number of protons (p)	Number of electrons (e)	Number of neutrons (n)
P	11	11	12
Q	18	18	22
R	15	18	16
S	11	10	14

 

 (a) Which of the P,Q,R, S is electricity neutral ?

(b) Which of the species is negatively charged ?

(c) Which of the given atoms /ions are metals?

(d) Which atom/ion in the table is an isotope of the atom with the composition of 11p, 11e and 14n and why ?

 [B] X and Y are the two atomic species with following configuration : (1*4=4)

Atoms	Number of protons	Number of neutrons
X	8	8
Y	8	10

 

 (a) Are X and Y isobars?

(b) Do X and Y have different chemical properties?

(c) Do X and Y have different physical properties

(d) Are X and Y the atoms of different elements ?

II. Give one word for the following: (I Mark)

1. The subatomic particle discovered by JJ. Thomson and has negative charge.

2. The atomic model that depicts an atom as a positively charged sphere in which electrons are embedded.

3. The number of electrons present in the outermost shell or the combining capacity of an atom. 4. The number of protons present on the nucleus of an atom.

5. The atoms of different elements having same mass number and different atomic numbers.

 6. Doubly charged helium ions.

7. The arrangement of electrons in an atom.

8. The maximum number of electrons present in the n" shell of an atom.

9. The atomic model that represents atom as containing a heavy positively charged body at the centre with negatively charged particles moving around it.

10. The atomic model that states electrons move in definite orbits possessing definite amount of energy.

 

IV. FIll In the blanks : (I Mark)

1._________explained the presence of electrons by cathode ray experiment.

 2. The mass of an atom is decided by the number of__________and __________.

3. In his famous scattering experiment, Rutherford bombarded__________ on thin gold foil.

4. __________ is the sum of total number of protons and number of neutrons present in the nucleus of an atom.

5. The total number of protons in the nucleus of any atom is called __________.

6. Electrons are filled in an atom according to "2n" scheme that was suggested by __________.

7. ³⁵C₁₇ and ³⁷C₁₇ are the two __________of chlorine.

8. The subatomic particle not present in the nucleus of a hydrogen atom does not have  __________.

9. The atomic mass of an atom having 11 protons, 11 electrons and 12 neutrons is __________.

 10. Most of the mass of an atom is concentrated on its  __________

11. An  __________is the smallest unit of a substance that takes part in a chemical reaction.

12. The  __________ of any atom cannot have more than two electrons.

13. Isotopes are the atoms of __________ element, having same atomic number but different __________.

 V. State whether the following statements are True or False : (1 Mark)

1. α-particles are same as doubly charged helium ions.

2. Thomson's atomic theory states that the nucleus of an atom contains protons and neutrons.

 3. A proton has a mass that is much less than an electrons.

 4. An atom is the smallest particle of the matter.

 5. Atoms of an element may have more or less neutrons or electrons than other atoms of the same element.

 6. JJ. Thomson proposed that the atom is a positively charged sphere and electrons move around it.

7. The outermost atomic shell can hold a maximum of 18 electrons.

 

VI. Match the terms given in column I with those given in column II. (1 Mark)

 

COLUMN I	COLUMN II
1. Proton	(a) Bohr and Bury
2. Electron	(b) Thomson
3. Neutron	(c) Goldstein
4. Nucleus	(d) Chadwick
5. Distribution of electrons in a shell	(e)Rutherford

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