Which one of the following conclusions could not be derived from Rutherford's α-particle scattering experiment?
- (a)Most of the space in the atom is empty.
- (b)The radius of the atom is about 10⁵ times the radius of the nucleus.
- (c)Electrons move in a circular path of fixed energy called orbits.
- (d)Nearly all the mass of the atom resides in the nucleus.
Correct — C, 'Electrons move in a circular path of fixed energy called orbits.' Rutherford's gold-foil scattering (most α-particles passed straight through, a few were sharply deflected or bounced back) led to the nuclear model: the atom is mostly empty space, nearly all its mass sits in a tiny central nucleus, and that nucleus is far smaller than the atom. The experiment said nothing about electrons moving in fixed-energy orbits — that idea came later from Niels Bohr, so it could not be derived from Rutherford's experiment.
- (a)Most of the space in the atom is empty. — This could be derived — most α-particles passed straight through undeflected, showing the atom is mostly empty space, so it is a genuine Rutherford conclusion, not the exception.
- (b)The radius of the atom is about 10⁵ times the radius of the nucleus. — This could be derived — the rare sharp deflections showed the charge and mass are packed into a tiny central region, giving an atom about 10⁵ times larger in radius than the nucleus, so it fits Rutherford.
- (d)Nearly all the mass of the atom resides in the nucleus. — This could be derived — only a heavy, dense core could turn α-particles back, so almost all the mass lies in the nucleus; this is a Rutherford conclusion, not the answer.
In Rutherford's α-particle scattering experiment, a thin gold foil was bombarded with alpha particles. Most passed straight through, a few were deflected, and a very few bounced almost straight back. From this he concluded that the atom is mostly empty space with a tiny, dense, positively charged nucleus carrying almost all the mass — the nuclear model of the atom.
The exam trick is to mix a genuine Rutherford conclusion with a later idea. Fixed-energy electron orbits are a postulate of Bohr's model (1913), introduced to fix the instability of Rutherford's atom; the scattering data themselves reveal nothing about how electrons move.
- In the gold-foil experiment most α-particles passed straight through, a few deflected, and very few bounced back.
- The scattering showed the atom is mostly empty space, with the positive charge and nearly all the mass in a tiny central nucleus.
- The nucleus is roughly 10⁵ times smaller in radius than the whole atom.
- Electrons revolving in fixed-energy (quantised) orbits was Bohr's contribution, not Rutherford's.
Fixed-energy electron orbits came from Bohr, not from Rutherford's scattering data — the conclusion the question rules out.
- Assuming every statement about atomic structure came from Rutherford.
- Confusing Rutherford's nucleus with Bohr's fixed-energy orbits.
Asked as 'which conclusion is / is not from Rutherford's experiment?' or by comparing the Rutherford and Bohr models of the atom.
The alpha particle carries two positive charges. Its mass is very nearly equal to that of
- (a) two protons
- (b) an atom of helium
- (c) sum of masses of two positrons and two neutrons
- (d) two positrons as each positron carries a single positive charge
Answer(b) an atom of helium — an α-particle is a helium-4 nucleus (2 protons + 2 neutrons).
Same concept — the alpha particle, the very projectile used in Rutherford's scattering experiment that revealed the nuclear atom.
Which one of the following findings is NOT observed in Rutherford's Nuclear Model of Atom?
- (a) There is a neutral centre in an atom called nucleus
- (b) Nearly all the mass of an atom resides in the nucleus
- (c) The electrons revolve around the nucleus in a circular path
- (d) The size of a nucleus is very small as compared to the size of atom
Answer(a) There is a neutral centre in an atom called nucleus
Near-identical concept — separating genuine features of Rutherford's nuclear model from statements that do not belong to it.
Which one of the following particles in the nucleus of an atom was discovered by J. Chadwick?
- (a) Electron
- (b) Proton
- (c) Positron
- (d) Neutron
Answer(d) Neutron
Related — the make-up of the nucleus Rutherford discovered; the neutron was the later addition by Chadwick.
- practice — not a real PYQ
In Rutherford's α-particle scattering experiment, the fact that a few α-particles bounced almost straight back showed that
- (a)the atom is mostly empty space
- (b)the positive charge and mass are concentrated in a tiny nucleus
- (c)electrons revolve in fixed orbits
- (d)atoms are indivisible
Answer(b) the positive charge and mass are concentrated in a tiny nucleus — only a dense core could reverse the α-particles.
- practice — not a real PYQ
The idea that electrons revolve around the nucleus in fixed energy levels was proposed by
- (a)Rutherford
- (b)J. J. Thomson
- (c)Niels Bohr
- (d)James Chadwick
Answer(c) Niels Bohr — his 1913 model introduced quantised orbits.