Test: Atom Structure - September 28, 2022 - NEET MCQ

Electric discharge in partially evacuated tubes in cathode ray discharge tube. Cathodes rays are made up of electrons. There is a presence of negative charge in cathode rays, magnetic field deflects these rays. Cathode ray discharge tube needs high voltage.

The suitable conditions of cathode ray discharge tube are low pressure and high pressures. Pressure can be adjusted by evacuated tubes. High voltage is applied across electrodes and current starts flowing through the tube.

R. A. Millikan conducted oil drop experiment to measure the mass of oil droplets. After observation of how the charge is transferred in the experiment he concluded that charge only appears in integral multiples of e i.e. q = ne; n = ±1, ±2, ±3, etc.

Through cathode rays discharge tube experiments, he concluded that every substance in this universe is made up of electrons from his experiments. He observed how cathode rays move and the charge to mass ratio of it.

 Zinc sulfide is a phosphorescent material, which has been coated on the anode. when cathode rays strike on the anode, electrons hit on the Zinc sulfide screen, hence creating a bright spot.

In 1911, Rutherford discovered protons by performing experiments and also found out that positive charge is concentrated at centre and that it has most of the atomic mass. The name proton was first time given in the year 1920.

The mass of an electron is 0.00054 u. The mass of a proton is 1.00727 u. The mass of a neutron is 1.00867 u. Then mass of neutron by mass of an electron is 1.00867/0.00054 = 1838. Therefore the mass of neutron in terms of the electron is 1838 times.

Thomson proposed a model of the atom, in which electrons are embedded to make it as the stable electrostatic arrangement and such that positive charge is equally distributed around a sphere. Mass is assumed to be equally distributed. So. it has different names like plum pudding, watermelon and raisin pudding model.

Henri Becquerel discovered that elements emit radiation and termed this phenomenon as radioactivity. Later Curie on research found out about α-rays, β-rays and γ-rays. Later Rutherford concluded that α particles are helium nuclei.

For an element, Atomic number(Z) = number of protons in that atoms = numbers of electrons in that atom; Mass number = number of protons + number of neutrons. So Z = 13 and A = 13 + 14 = 27. Hence that element is Aluminium.