Thomson's model of atom J.J. Thomson in 1904, proposed that an atom was a sphere of positive electricity in which were embedded number of electrons. The stability of the atom was explained as a result of the balance between the repulsive forces between the electrons and their attraction towards the centre of the positive Sphere.This model is compared with a watermelon … [Read more...] about Rutherford’s Model of an Atom
Class 11
Discovery of Proton
Since the atom as a whole is electrically neutral and the presence of negatively charged particles in it was established ,therefore, it was thought that some positively charged particles must also be present in the atom. Goldstein in 1886 performed discharge tube experiment in which he took perforated cathode and a gas at low pressure was kept inside the tube, as … [Read more...] about Discovery of Proton
Discovery of Electron
William crookes in 1879 studied the conduction of electricity through gases at low pressure. EXPERIMENTAL SET UP 1) He took a discharge tube which is a long glass tube, sealed at both the ends and fitted with two metal electrodes. 2) It has a side tube fitted with a stop cock which can be connected to a vacuum pump to reduce the pressure of the gas inside to any … [Read more...] about Discovery of Electron
Atomic and Molecular mass
As an atom is so small a particle that it cannot be seen or isolated ,therefore it is impossible to determine the actual mass of a single atom by weighing it. The problem was finally solved by Avogadro's hypothesis. If equal volumes of two different gases are taken under similar conditions of temperature and pressure and then weighted, the ratio of their masses will be … [Read more...] about Atomic and Molecular mass
Avogadro’s Hypothesis
Berzelius a Swedish chemist, gave a hypothesis called Berzelius hypothesis which states that: Equal volume of all gases under similar conditions of temperature and pressure contain equal number of atoms. For Example: Hydrogen + Chlorine → 2 Hydrogen chloride gas 1 vol 1 vol 2 vol n atoms n atoms … [Read more...] about Avogadro’s Hypothesis