CBSE Class 9 Answered

1. According to Rutherford, atom has a small, dense, positively charged nucleus with electrons orbiting around the outside. The major problem with this concept was that as a charged particle moves, it must radiate energy. Eventually, the electrons orbiting around the nucleus would lose whatever energy got them there in the first place. Then, once the energy has been lost, there's nothing to keep the negatively charged electrons from being pulled into the positively charged nucleus, and having the atom implode.

Bohr came up with the concept of having electrons carry fixed amounts of energy (quanta) that keeps them at a certain distance from the nucleus. In order to be drawn into the nucleus, they have to give off that quanta of energy, and they can't do that from the lowest energy position.

2. The Rutherford’s model of atom does not say anything about the arrangement of electrons in an atom.