In the previous video, we learnt about Ruderford's nuclear model. Thomsen gave the name electron to negatively charged particles and proton to the positively charged particles. What was the shortcoming of Ruderford's nuclear model? By law of physics, the electron revolving around the nucleus goes on decreasing its energy, which will spiral electron into nucleus making the atom unstable. This difficulty was solved by Neel's Bohr in 1913 by putting forward stable orbit atomic model. His postulates were first postulate. The electrons are revolving around the nucleus lie in concentric circular orbits, which are at a certain distance from the nucleus. Second postulate. The energy of electron is constant while it is in a particular orbit. And third postulate. When an electron jumps from an inner orbit to an outer orbit, it absorbs energy. When an electron jumps from outer orbit to inner orbit, it emits energy. This absorption or emission of energy is equal to the difference in energy levels of the two orbits. Bohr name this orbits or energy shells as KLM and N. Starting from the shell closes to the nucleus. So which shell is closest to nucleus? K shell. So we can represent Bohr's stable orbit atomic model as positively charged nucleus. Electrons rotating in these orbits further studies and experimentation with radioactivity predicted one more subatomic particle. This was discovered by Shadwick in 1932 and he named it neutron which was present in the nucleus along with protons. Protons and neutrons are together called nucleons. Let's now study the properties of subatomic particles of the atom by preparing a table. Properties of subatomic particles in the atom subatomic particle electron with position as extra nuclear part in orbit or shells where charge on electron is negative which is minus 1.6 into 10 raise to minus 19 coulomb and mass of electron is 9.1 into 10 raise to minus 31 kg which is 1800 times less than hydrogen atom. Subatomic particle proton its position is at nucleus. The charge on protons positive which is plus 1.6 into 10 raise to minus 19 coulomb and mass of electron is 1 Dalton is equal to 1.66 into 10 raise to minus 27 kg. Subatomic particle neutron its position is at nucleus it has no charge. The mass of neutron is 1 Dalton is equal to 1.67 into 10 raise to minus 27 kg which is almost equal to that of proton. The maximum number of electrons that can be accommodated in a particular orbit is given by 2 n raise to 2 where n is equal to orbit number. So find out how many maximum electrons can be accommodated in each shell maximum capacity of shells showing the maximum number of electrons that can be accommodated. For n is equal to 1 that is K shell the maximum number of electrons that can be accommodated is equal to 2 n square is equal to 2 into 1 square which is equal to 2. For n is equal to 2 that is L shell the maximum number of electrons that can be accommodated is 2 n square is equal to 2 into 2 square which is equal to 8. For n is equal to 3 that is M shell. The maximum number of electrons that can be accommodated equal to 2 n square which is equal to 2 into 3 square which is equal to 18 and for n is equal to 4 that is N shell the maximum number of electrons that can be accommodated is equal to 2 n square which is equal to 2 into 4 square which is equal to 32. Thus first shell can accommodate maximum of 2 electrons. Second shell 8 electrons third shell 18 electrons and fourth shell 32 electrons and so on. But if second third shell is the outer shell it can accommodate a maximum of only 8 electrons and if first orbit is outermost orbit it can accommodate only 2 electrons. Summary in this video we learnt how both improved upon the Rudolfoor's planetary model. We also learnt about model atomic model. Subatomic particles electrons are 1800 times lighter than hydrogen atom and are revolving in shells around the nucleus. Now answer the following question. For aluminium find number of electrons, protons and neutrons. Also write electronic configuration in numerical form.