Atoms and Nuclei Test - 4

All the alpha particles were expected to pass through the gold foil with very little or no scattering, according to the JJ Thomson's "Plum pudding model". 

For standardization, a specific atomic nucleus (carbon-12) had to be chosen because the average mass of a nucleon depends on the count of the nucleons in the atomic nucleus due to mass defect. This is also why the mass of a proton or neutron by itself is more than (and not equal to) 1 u.

These are the elements having same atomic number but different mass number. They have the same atomic number because the number of protons inside their nuclei remains the same. The difference in their mass number is due to the difference in their number of neutrons.

Ernest Rutherford who was a former research student of JJ Thomson supervised the experiment carried by two of his students Hans Geiger and Ernst Marsden. Rutherford felt that there existed a nucleus at the centre of the atom having positive charge and thus proposed the Rutherford model.

At this instant, the alpha particle is momentarily at rest and the initial Kinetic energy is entirely converted to electrostatic potential energy.
Kinetic energy = Potential energy

There is an intimate relationship between the internal structure of an atom and the spectrum of radiation emitted by it.

This atom model was proposed by JJ Thomson before the discovery of the atomic nucleus. When Thomson discovered the negative electron, he realized that atoms had to contain some positive charge material equal to the negative electrons – otherwise the atom wouldn't be electrically neutral. According to this model, the positive charge of the atom is uniformly distributed throughout the volume of the atom and the negatively charged electrons were embedded in it like seeds in a watermelon.

The electrons revolve round their permitted orbits with acceleration and continuously radiate energy in the form of electromagnetic waves. Due to this continuous loss of energy, they would spiral inward and eventually fall into the nucleus.(Classical theory)

The unified atomic mass unit (u) is defined as one twelfth of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at rest.

Isotopes are variants of a particular chemical element which differ in neutron number. All isotopes of a given element have the same number of protons in each atom.

Free neutrons are unstable. A free neutron (n⁰) decays into a proton (p⁺), an electron (e⁻), and an electron antineutrino (νe¯). This phenomenon is called beta decay.

mass number (A) = total number of nucleons = number of protons + number of nutrons = atomic number (Z) + neutron number (N).

This expectation was based on the knowledge of the "Plum pudding model", proposed by JJ Thomson, where the positive charge and the negatively charged electrons were distributed throughout the whole atom. According to this model, all the alpha particles in the beam should pass through the foil without much scattering. However this experiment of Geiger-Marsden proved the Thomson's model wrong. 

Two nuclides are isotones if they have the same neutron number N, but different proton number Z. For example, boron-12 and carbon-13 nuclei both contain 7 neutrons, and so are isotones.