Basic Modern Physics
9.0 Early Atomic Structures
9.0 Early Atomic Structures
J.J.Thomson Atomic Model:
He suggested that atoms are just positively charged lumps of matter with electrons embedded in them like raisins in a fruit 
cake. It is also called as "Plum pudding" model.
cake. It is also called as "Plum pudding" model. Rutherford's Nuclear Model of Atom:
- Experiment: A narrow beam of $\alpha $-particles was directed onto a gold foil about 1$\mu m$ thick.
- Observation: He found that some of the particles were scattered appreciably while others passed through with zero or a little deflection. A very few-about of $1$ in $8000$ suffered deflection of more than ${90^0}$.
- Rutherford's explanation: The center of the atom can be thought as if the whole mass and nearly all positive charge is concentrated in it. And the electrons revolve around it in circular orbits, held by electrostatic force of attraction which provide the centripetal acceleration.
- Shortcomings:
- According to classical physics any charged body accelerating around a orbit loses energy continuously. Hence, electron should lose energy and undergo a spiral path with a decreasing radius into the nucleus within a fraction of second. This states that atom is unstable, but in contrary atom is quite stable.
- Due to continuously changing radii of the circular orbits of electrons, the frequency of revolution of the electrons must be changing. As a result, electrons will radiate electromagnetic waves of all frequencies, i.e, the spectrum of these waves will be continuous in nature.But experimentally the atomic spectra are not continuous. Instead they are line spectra.
