Page 95 - ICSE Chemistry 8

B. Read the following paragraph. Iden fy the incorrect parts.
An atom is posi vely charged. This suggests that the number of posi vely charged par cles present
in an atom are more than the number of nega vely charged par cles. E. Goldstein, a French scien st,
performed an experiment in the glass rod, with a perforated anode. During the experiment, he
observed another set of rays moving in direc on opposite to that of the anode rays. Since these
rays originated from the cathode, they were named as cathode rays. They were also called discharge
rays. The cathode rays consist of the posi vely-charged par cles called electrons.

C. Answer in detail.

1. Write a note on ancient view on atomic structure.
2. Write the postulates of Dalton’s atomic theory.
3. Discuss J.J. Thomson’s experiment performed for the discovery of electron.

4. Write a note on discovery of nucleus.
5. Write a note on discovery of neutron.

6. Discuss the modern concept of an atom.
7. Write a note on structural stability of an atom.

8. Discuss the forma on of electroposi ve ions and electronega ve ions.

OBSERVE AND PERFORM

Observe the given image carefully and answer the following ques ons.

1. Name the element represented through the image.

2. What is the atomic number and mass number of the element?
3. Write the number of electrons, protons and neutrons in the element.

APPLY YOUR LEARNING

A. Name the model that displaced Thomson’s model of an atom. Was this model able to explain the
stability of an atom?
B. Zain wants to know how the electrons are able to maintain their posi on in the orbits. Help him to
understand the reason behind this.
C. Why do the isotopes of elements show same chemical proper es?

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