Question

How does Rutherford's model link to Thomson and Bohr's model of an atom?

Answer 1

J J Thomson's atomic model:

• J J Thomson proposes a detailed model of the atom with his cathode ray scope experiment.
• Thomson determined that all matter, whatever its source, contains particles of the same kind that are much less massive than the atoms of which they form a part and are now called electrons.
• He developed the idea that atoms are made of negative electrons embedded in a gel of positive charge.
• This model is also known as the raisin pudding model or watermelon model.
• This model assumed that mass of the atom is evenly spread over the entire atom.
• This model could explain the electrical neutrality of atoms but failed to explain the observation of Rutherford's alpha-particle scattering experiment.

Rutherford's atom model:

• Ernest Rutherford proposes a detailed model of the atom with his gold foil experiment.
• Most of the mass and all the positive charge of an atom are concentrated in a very small region called the nucleus and the size of the nucleus is extremely small when compared to the size of the atom.
• The positive charge on the nucleus is due to protons and the magnitude of the charge on the nucleus is different for atoms of different elements.
• The nucleus is surrounded by negatively charged electrons that revolve around it at very high speeds and the electrostatic force of attraction between the electrons and the nucleus is balanced by the centrifugal force acting on the revolving electrons.
• The total negative charge on the electrons is balanced by the total positive charge on the nucleus so that atom on the whole is electrically neutral.
• Most of the space inside the atom is empty.
• Rutherford's atomic model is also known as the planetary model of the atom.

Bohr's model of an atom:

• Bohr's atomic model is based on the quantum mechanical aspect.
• Electrons revolve around the nucleus in a fixed circular path which is called orbits also known as stationary states.
• Each orbital is characterized by a quantum number '$\mathrm{n}$' with values designated as $\mathrm{n}=1,2,3\mathrm{etc}$ or can be represented as $\mathrm{K},\mathrm{L},\mathrm{M},\mathrm{N}...\mathrm{etc}$.
• Higher the value of $\mathrm{n}$, the greater will be the energy of the electron in that orbit and the energy associated with a certain orbit increase in the distance from the nucleus.
• As long as an electron remains in a particular orbit, it will not lose or gain energy.
• Revolving electrons can absorb or emit energy in fixed amounts

Correlation between Rutherford's model, Thomson and Bohr's model of an atom:

• Thomson and Rutherford said that there are negative and positive charges in an atom.
• Thomson describes a sphere, and Rutherford describes orbiting around the nucleus, which is also sphere-shaped.
• Thomson and Bohr said that the electrons revolve around the nucleus.
• Both agreed that the electron occupies a large space of the atom.