Structure of the Atom
An Atoms contain three basics particles namely Proton, neutrons, and electorns .The nucleus of atoms contain Proton and neutrons, where Proton are positively charged and neutrons are neutral .The electrons located at the outermost Regine called electron shall .
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| Structure of Atoms |
Electron : JJ Thompson discovered negatively charged sub-atomic particles electron , emmited by the Cathode towards the anode in the cathode ray experiment , these negitvaly charged particles are electrons.
Protons : Eugen Goldstein discovered that with a different condition in the same chamber Anode emitted positively charged particles known as canal ray or later name as protons.
Neutron : J. Chandwick ,discovered a sub - atomic particle with no charge and a mass equivalent to proton in the nucleus of all atoms.These nuterally charged particles are neutrons .
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| structure of atom class 9 notes |
Thompson Model of an Atom :- According to the Thompson an atoms consist of a positively charged sphere and the electrons are embedded in it .
ii)- The negative and positive charges are equal in magnitude , so the atom as a whole is electrically neutral.
Thompson atomic model is compared to Watermelon, where he considered seeds as negatively charged particles and red part of the watermelon as positively charged.
Thompson atomic model is compared to Watermelon, where he considered seeds as negatively charged particles and red part of the watermelon as positively charged.
Limitation of Thompson's model :
> Thompson structure of an atom failed to explain the arrangement of protons and electrons in its structure.
> Also failed to explain stability of atoms.
Rutherford's model of an atom : -
Rutherford conduct an experiment and Bombarding the alpha particles on a gold foil . He observed the path of the alpha particles after passing through an atom and drafted some postulate.
> Most of the space in an atom is empty as the particles passed through the gold foil without and hindrance .
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| Rutherford's Model of an atom |
> The positively charged center is called the nucleus and the mass of an atom reside in the center.
> The particles deflected 180 degree after bombarding the nucleus.
> The size of the nucleus is small compared to the total size of the atom.
> Positive and negative charges balance with each other
Drawbacks of the Model :
> The electrons revolve in an unstable path and they undergo acceleration energy, when the electron revolve they lose energy. Soon electron would collapse into the nucleus
> The tendency would make an atom highly unstable while the atoms is highly stable .
>It also failed to explain the atomic number concept as it explained only presence of protons in the nucleus .
Bohr's Model of an Atom
To overcome of drawbacks of Rutherford Neil Bohr proposed modified model of structure of atom.
> Electrons revolve around the necleus in stable orbits without emission of radiant energy.
> Each orbit has a definite energy and is called an energy shell or energy level.
> An orbit is designated a K,L,M,N shell when the electron is in the lowest energy level it is said to be in ground state .
> An electron absorbe energy when it jumps from one orbit to another .
Orbit : orbits are the energy shell surrounding the nucleus in which electrons revolve