Class 9 : Important Points - Structure of Atom Class 9 Notes | EduRev
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- Discharge tube studies by J.J. Thomson and other led to the discovery of electron.
- J.J. Thomson determined the value of charge/ mass ratio, e/m of the electron.
- R.A. Millikan determined the value of charge on the electron.
- Positive rays were discovered by E. Goldstein and these are also called canal rays.
- Rutherford and his co-workers performed a-particle scattering experiments which led to the discovery of atomic nucleus.
- Atoms of the same element which have the same atomic number but different mass number are called isotopes.
- Atoms of different elements having same mass number but different atomic number are called isobars.
- Bohr’s model of an atom gave the concept of orbits or shells. These are designeted as K, L, M, N,
- Each orbit has a definite energy and that is why these are also called energy levels or energy shells.
- Neutron was discovered by Chadwick.
- The number of protons in an atom of an element is known as atomic number.
- The sum of the number of protons and neutrons in an atom of the element is called mass number.
- In general, the maximum number of electrons that can be present in any shell is 2n2 where n is the number of energy shell.
- The distribution of electrons in different energy shells is called electronic configuration. Electronic configuration of atoms are written with the help of K, L, M, etc.
- The electrons present in the outermost orbit (or valence shell) are called valence electrons.
- The valency of atom is either no. of electrons in valence shell or 8 – no. of electrons in the valence shell.