Rutherford's \(\alpha\)-particle scattering experiment give the experimental evidence for deriving the conclusion that
(i) Most of the space inside the atom is empty
(ii) The nucleus of an atom is positively charged.

3

(a)

How does Bohr model of atom explain characteristic spectra of different atoms and ionisation in the of gases in the discharge tube experiment?

3

(a)

State the suggestions made by Bohr and Bury with regard to distribution of electrons in different energy levels in the atoms of element.

3

(a)

State the three rules that are followed for determining the number of electrons in different energy levels or shells in an atom.

3

(a)

Define the term "Half-life".

3

(a)

A radioisotope has half-life of 900 seconds.Calculate the fraction of original isotope which would remain behind after four half-life periods.

3

(a)

The half-life period of Actinium is 15 seconds.Starting with 0.1g of Actinium, how much would be left at the end of one minute?

3

(a)

Give reasons for the following:
(a) Isotopes of an element are chemically similar
(b) An atom is electrically neutral
(c) Noble gases show least reactivity
(d) Nucleus of an atom is heavy and positively charged.
(e) Ions are more stable atoms.

3

(a)

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

3

(a)

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

3

(a)