Who discovered natural radioactivity?

What are the limitations of J.J. Thomson’s model of atom?

What are the limitations of Rutherford model of the atom?

Describe Bohr's model of the atom ?

Compare all the proposed models of an atom given in this chapter.

Summarize the rules for writing of distribution of electrons in various shells for the first eighteen elements.

Define valency by taking examples of silicon and oxygen.

Explain with examples, (i) Atomic number, (ii) Mass number, (iii) Isotopes, and (iv) Isobars. Give any two uses of isotopes also.

Na⁺ has completely filled K and L-shells. Explain.

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