STRUCTURE OF THE ATOM
1. Electron was discovered by J.J.Thom son and proton by Goldstein.
2. The mass of proton was 2000 times as that of electron.
3. The mass of proton is taken as unit charge and its charge is +1, mass of electron is negligible and its charge is minus one.
4. J.J.Thomson proposed a model which states that an atom consist of a positively charged sphere and electrons are embedded in it.
5. He also stated that +ve and —ve charges are equal in magnitude and atom as a whole is electrically neutral.
6. Rutherford’s scattering experiment discovered fast moving (a) particles and also atomic nucleus.
7. Rutherford’s model states that atomic nucleus is +vely charge and lies in the centre, and electrons revolve around nucleus in well-defined orbits, size of nucleus is very small.
8. Rutherford could not explain the stability of an atom.
9. Neils Bohr suggested that electrons revolve in discrete orbits and does not radiate energy. If the atomic shells are complete then atoms are stable and less reactive.
10. J. Chadwick discovered subatomic particle with no charge called neutron.
11. Maximum number of electron present in a shell is given by formula 2n2.
12. The maximum number of electrons that can be accommodated in outermost orbit is 8 is called octet.
13. To maintain octet atoms share, lose or gain the electrons.
14. Valency is the combining capacity of an atom.
15. Atomic number is the total number of protons present in nucleus of an atom.Represented by Z.
16. Mass number ¡s sum of total number of protons and neutrons present in nucleus of atom.
17. Isotopes are atoms of same elements which have different mass number, and isobars are atoms with some mass number but different atomic number.
