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Why an electron has a negative charge and that of a proton has positive?

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It is difficult to answer that why electron has negative charge just like it is difficult to answer other naturally existing things.

It was J.J. Thomson in 1897 who discovered sub atomic particles in an atom and named it as electron. J.J Thomson performed cathode rays experiment to find the charge of an electron. Rays were emitted at the cathode in a discharge tube, the negatively charged particles which were repelled are attracted to the anode so the rays must be negatively charged.

After the discovery of the electron, Rutherford thought that there must be positive charge particles within the atom to balance the negative electrons. Rutherford's discovery positive charged particles and named it as proton by performing gold foil experiment.

For more details about the experiment follow the link provided.

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kavya--kammana | Student

( some important points are given below. you may understand how electrons and protons got their name )( read carefully otherwise nothing will be understood)

  • electron is the first identified particle in an atom
  • the electron is a fundamental particle discovered by J.J Thomson during the study of conduction of electricity through gases taken in a gas discharged tubes.
  • it is now known that some invisible rays are formed at cathode of tube and when trays strike glass tubes they emit greenish light.
  • since these rays are formed at the cathode they are known as cathode rays.
  • the particles present in cathode rays are called electrons.
  • you may know that gas will get ionized when electricity is passed through it at low pressure.
  • these electrons and net possitive particles will flow to the oppositely charged electrodes.
  • like this those that flow to +ve electrode are -ve rays and those that flow to -ve electrode are +ve rays.
  • the particles of +ve rays are protons and particles of -ve rays are callesd electrons.
  • atoms donot have charge bcoz +vely charged protons and negatively charged electrons are in same number.
  • so to maintain a balance of charge of atom opposite charges have to be there .
  • thats why one is -ve and one is +ve
  • if there were only electrons in an atom then we have to say that atom is negativly charged and vise versa. 
jasonjohnson159 | Student
electron is itself a fundamental negative particle while protonic positive charge is due to presence of 3 quarks in it neutron also has 3 quarks but no charge. The electron is a subatomic particle that carries a negative electric charge. It has no known substructure and is believed to be a point particle Electrons participate in gravitational, electromagnetic and weak interactions. Like its rest mass and elementary charge, the intrinsic angular momentum (or spin) of an electron has a constant value. In the collision of an electron and a positron, the electron's antiparticle, both are annihilated. An electron–positron pair can be produced from gamma ray photons with sufficient energy. The concept of an indivisible amount of electric charge was theorized to explain the chemical properties of atoms, beginning in 1838 by British natural philosopher Richard Laming;[4] the name electron was introduced for this charge in 1894 by Irish physicist George Johnstone Stoney. The electron was identified as a particle in 1897 by J. J. Thomson and his team of British physicists. Electrons are identical particles that belong to the first generation of the lepton particle family. Electrons have quantum mechanical properties of both a particle and a wave, so they can collide with other particles and be diffracted like light. Each electron occupies a quantum state that describes its random behavior upon measuring a physical parameter, such as its energy or spin orientation. Because an electron is a type of fermion, no two electrons can occupy the same quantum state; this property is known as the Pauli exclusion principle. In many physical phenomena, such as electricity, magnetism, and thermal conductivity, electrons play an essential role. An electron generates a magnetic field while moving, and it is deflected by external magnetic fields. When an electron is accelerated, it can absorb or radiate energy in the form of photons. Electrons, together with atomic nuclei made of protons and neutrons, make up atoms. However, electrons contribute less than 0.06% to an atom's total mass. The attractive Coulomb force between an electron and a proton causes electrons to be bound into atoms. The exchange or sharing of the electrons between two or more atoms is the main cause of chemical bonding Electrons were created by the Big Bang, and they can be annihilated during stellar nucleosynthesis. Electrons are produced by cosmic rays entering the atmosphere and are predicted to be created by Hawking radiation at the event horizon of a black hole. Radioactive isotopes can release an electron from an atomic nucleus as a result of negative beta decay. Laboratory instruments are capable of containing and observing individual electrons, while telescopes can detect electron plasma by its energy emission. Electron plasma has multiple applications, including welding, cathode ray tubes, electron microscopes, radiation therapy, lasers and particle accelerators.