Structure of the atom Worksheet-3

Structure of the atom Worksheet-3

1. Rutherford's alpha-particle scattering experiment was responsible for the discovery of

A. Atomic Nucleus                       B. Electron

C. Proton                                        D. Neutron

2. Isotopes of element have :

A. the same physical properties

B. different chemical properties

C. different number of neutrons

D. different atomic numbers

3. Number of valence electrons in Cl^– ion are :

A. 16                    B. 8                     C. 17                    D. 18

4. 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

5. Out of the three sub-atomic particles known, which is called universal particle ?

A. Electron        B. Proton           C. Neutron

6. Which of the following statements regarding cathode rays is incorrect?

A. Cathode rays travel from cathode towards anode

B. Cathode rays consist of material particles

C. Properties of the cathode rays depend upon the nature of the gas enclosed in the discharge tube

D. Cathode rays are made up of electrons.

7. An electron is known as universal particle because :

A. its charge is always fixed

B. its mass is always fixed

C. it is always present in cathode rays

D. Its charge and mass remain fixed whatever may be the source of its emission.

8. The atom which does not contain neutron in the nucleus is:

A. protium         B. deuterium    C. tritium           D. helium

9. The alpha particles are the same as :

A. protons                                      B. helium atoms

C. helium nuclei                           D. Lithium nuclei

10. The nucleus of an atom of phosphorus is represented as ₁₅P³¹. The number of protons, neutrons and electrons in the atom of phosphorus are respectively :

A. 15,31,15         B. 15,15,16         C. 15, 16, 15       D. 15, 31, 16.

Answer:

1. A

2. C

Explanation: Isotopes have same atomic number hence have similar chemical properties. They have different number of neutrons hence their mass number is different.

3. B

Explanation: Cl^– Ion has 18 electrons (17+1). Hence the number of valence electrons in Cl^– ion is 8.

Electronic distribution:

Cl – 2,8,7

Cl^– – 2,8,8

4. D

5. A

Explanation: Electron is known as universal particle.

6. C

Explanation: Properties of cathode rays do not depend on the nature of gas enclosed in the discharge tube. Cathode rays consist of stream of negatively charged particles called electrons.

7. D

8. A

9. C

Explanation: He²⁺ 2 protons and 2 neutrons

10. C