Question

1. where is most of the mass of an atom concentrated? 2) why was the plum pudding model replaced with the nuclear model? 3) why did niels bohr suggest that electrons orbit at fixed distances? below is a table showing different properties of the atom. number the statements to show the order in which they were discovered: positive atomic nucleus, neutrons, electrons, protons, electron shells

Explanation:

1. The mass of an atom is concentrated in the nucleus because protons and neutrons, which have significant mass, are located there. Electrons have very little mass compared to protons and neutrons.
2. The plum - pudding model was replaced with the nuclear model because experiments such as the gold - foil experiment by Rutherford showed that the positive charge and most of the mass of the atom are concentrated in a small, dense nucleus, which the plum - pudding model could not explain.
3. Niels Bohr suggested that electrons orbit at fixed distances to explain the discrete spectral lines of hydrogen. His model proposed that electrons could only occupy certain energy levels or orbits around the nucleus, and when they transition between these levels, they emit or absorb photons with specific energies corresponding to the energy differences between the levels.

Answer:

1. In the nucleus.
2. Due to experimental evidence like Rutherford's gold - foil experiment.
3. To explain discrete spectral lines of hydrogen.