Size of the nucleus of an atom is ______ as compared to the size of the atom.

Who discovered the neutron?

What is the number of valence electrons in the chlorine atom?

Identify the pair of isotopes from the following:

¹⁶₈X, ¹⁶₇X, ¹⁷₈X,

There are 15 protons and 16 neutrons in the nucleus of an element. Calculate its atomic number and mass number.

(a) Why is Thomson’s model of an atom compared with watermelon?

(b) Why do isotopes have different mass numbers?

The number of electrons in the outermost shell of chlorine is 7. What is its valency and why?

Write one pair of isobars. Why the chemical properties of isobars are not similar?

In the following table, the mass number and the atomic number of certain elements are given:

(a) Select a pair of isobars from the above table.

(b) What would be the valency of element ‘B’ listed in the above table?

(a) List any two postulates of Bohr’s model of an atom.

(b) Draw a sketch of Bohr’s model of an atom with four shells

(c) name the three sub-atomic particles.

(a) What are the canal rays? State the nature of the constituents of canal rays.

(b) Who discovered canal rays?

Define valence of an element. Find the valency of chlorine and magnesium (At. No. of chlorine = 17, magnesium = 12).

Complete the following table:

The chlorine atom is electrically neutral but chloride ion is charged. Explain.

(a) Write the name of the sub – atomic particle discovered by J. Chadwick. What type of charge occurs on this particle? In which part of an atom this particle is located?

(b) List three steps of an experiment performed by Rutherford for his model of an atom.

(c) Define isobar, write its one example.

(d) Which scientist concluded that the size of the nucleus is very small as compared to the size of an atom?

(a) What is an octet? How do elements reach an octet?

(b) Make a schematic atomic structure of Magnesium of Phosphorus.

(Given: number of protons of Magnesium = 12, Phosphorus = 15).

(a) What are isobars? Give one example.

(b) Write two differences between isobars and isotopes.

(c) Write any two uses of isotopes.