Question

Can someone kindly explain the meaning of the following paragraph? I would be much obliged. Very few of the particles, the ones at the centre almost retraced their path. This meant they were strongly repelled by a positively charged body at the centre of the atom. This positively charged body is called the nucleus. Since the electron has negligible mass, the mass of the atom is concentrated in the nucleus. Please explain the above paragraph. CLASS: 8 SUBJECT: CHEMISTRY CHAPTER: THE ATOMIC STRUCTURE PORTION: DISCOVERY OF NUCLEUS

Answer 1

Explanation:

Now, you must be talking about the Rutherford's Gold foil experiment to discover the atomic nucleus. So, let me begin from the beginning.

Rutherford took a radioactive element and passed a ray from that element through a gold foil which struck to a fluorescent screen. Now, he noticed 3 changes:

1. Many alpha particles (these particles are released when a radioactive element destroys and emits rays) that passed through the gold foil had no deflection.
2. Some of the were deflected at little angles.
3. Very few of them went back to the path they came to pass the gold foil.

From basically the third point, he concluded that the centre of the gold foil (atom) must have a mass due to which the ray went back when it struck it. Thus, this means that atom which is mostly a vacuum entity has a mass on its centre due to which the rays were deflected and went back rather than passing through it. This led to the discovery of atomic nucleus. Also, Lord Rutherford stated that the nucleus must have a positive charge due to which the rays, consisting of an opposite charge were deflected (Positive-negative repulsion like magnets). This also proved that protons lie in the nucleus.

Hope this helps.