Question

Describe Rutherford's model of an atom.What were the short comings of this model.How were these addressed by bohr in his model of an atom.

Answer 1

Rutherford found an atom proton

Answer 2

Rutherford's model of an atom

<> There is a positively charged centre in an atom called nucleus.

<> Nearly all the mass of the atom resides inside the nucleus

<> The size of the nucleus is very small compared to the size of the atom

<>The electrons revolve around the nucleus in well-defined orbits.

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Shortcomings or drawbacks of the model :-

<> During acceleration , the electrons would radiate energy.

<> As a result , the electrons would radiate energy.

<> Gradually , the electrons would lose energy and as a result , fall into the nucleus.

<> If this were so , the atom would be highly unstable , and thus matter would not exist

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Bohr addressed the drawbacks by giving some postulates of Bohr's model :

a) Electrons revolve round the nucleus in a fixed orbit known as " discrete orbits of electrons "

b) While revolving around the orbits , the electrons would not radiate energy

c) The maximum number of electrons that can be accommodated in a shell is given by the formula 2n² , where n is the energy level or orbit number.
1st orbit is denoted by K
2nd orbit is denoted by L
3rd orbit is denoted by M, and so on.


K shell = 2 × 1² = 2 electrons

L shell = 2 × 2² = 8 electrons 

and so on ........



d) The outer shells cannot be filled unless inner shells are filled.

e)The outermost shell of an atom cannot accommodate more than 8 electrons, even if it has a capacity to accommodate more electrons.