Discovery of Electron

Who uncovered the electron?

Electron was found by J. J. Thomson in 1897 once he was studying the nature of cathode ray.

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Figure 1. J. J. Thomson winner Nobel prize in 1906 for discovering the elementary particle electron. Interestingly, his kid G. P. Thomson additionally won the Nobel compensation in 1937 because that proving the wavelike nature of electron.1

What is cathode ray?

J. J. Thomson created a glass tube which was partially evacuated i.e. Much of the air to be pumped the end of the tube. Climate he applied a high electric voltage between two electrodes in ~ either finish of the tube. That detected that a stream of fragment (ray) was coming out from the negatively charged electrode (cathode) come positively fee electrode (anode). This ray is called cathode ray and also the whole building and construction is referred to as cathode ray tube. The schematic the a cathode beam tube is offered in figure 2.

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Figure 2. Cathode beam tube

Properties the cathode beam particle

1. They take trip in right lines.

2. They room independent that the material composition of the cathode.

3. Using electric field in the course of cathode ray deflects the ray towards positively charged plate. For this reason cathode ray consists of negatively fee particles.

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Figure 3. Deflection of cathode rays in the direction of positively charged plates

J. J. Thomson measured the charge-by-mass-ratio (e/m) the cathode ray bit using deflection in both electric and also magnetic field.

(fracem = -1.76×10^8) coulomb every gram

The cathode ray bit turned out to be 2000 times lighter than hydrogen.

Although we got e/m ratio for electron native J.J. Thomson’s Cathode ray Tube experiment, we still don’t recognize the exact charge (e) for electron. American physicist Robert Millikan design an experiment to measure up the absolute worth of the charge of electron i m sorry is disputed below.


Millikan Oil fall Experiment

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Figure 4. Robert Millikan found charge of electron and won Noble prize in physics in 1923.2

In 1909, American physicist R. Millikan measure up the fee of an electron making use of negatively fee oil droplets. The measured charge (e) of an electron is (-1.60×10^-19) Coulombs.

Using the measured charge of electron, we have the right to calculate the massive of electron indigenous e/m ratio offered by J. J. Thomson’s cathode beam experiment.

(fracem= -1.76×10^8) Coulomb-per-gram

(m = frace-1.76×10^8)

Putting (e = -1.60×10^-19) Coulomb,

(m=9.1×10^-28) gram.

What we have learned

Electron was uncovered by J. J. Thomson in Cathode beam Tube (CRT) experiment.Electrons room negatively fee particles with charge-to-mass ratio (-1.76×10^8) C/gmThe fee of one electron was measured by R. Millikan in Oil fall experiment.Charge of an electron is (-1.60×10^-19) CMass of an electron is (9.1×10^-28) gram.Electron is around (2000) times lighter than hydrogen.

Discovery of Proton
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Figure 5. Schematic yellow foil experiment

In 1909, Rutherford found proton in his renowned gold silver paper experiment.

Gold foil Experiment

In his gold foil experiment, Rutherford bombarded a beam that alpha corpuscle on an ultrathin yellow foil and also then recognize the scattered alpha corpuscle in zinc sulfide (ZnS) screen.

Results

Most of the corpuscle pass with the silver paper without any deflection.Some that the alpha particles direction at small angle.Very couple of even bounce ago (1 in 20,000).

Conclusion

Based ~ above his observations, Rutherford suggest the complying with structural features of an atom:


Most of the atom’s mass and also its whole positive charge room confined in a small core, referred to as nucleus. The positive charged particle is called proton.Most the the volume of an atom is empty space.The variety of negatively fee electrons spread outside the cell core is very same as variety of positively charge in the nucleus. It defines the in its entirety electrical neutrality of one atom.

Discovery that Neutron

From the ahead discussion, we can see the the gold foil experiment provided a clear snapshot of the framework of an atom which is composed of protons (nucleus) and also same variety of electrons outside of the nucleus.

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Figure 6. Schematic diagram because that the experiment that caused the discovery of neutron by Chadwick. $$_4^9Be + _2^4α longrightarrow <_6^13C> longrightarrow <_6^12C> + _0^1n$$But researchers soon realized that the atomic model available by Rutherford is not complete. Various experiments showed that massive of the cell nucleus is around twice 보다 the variety of proton. What is the origin of this extr mass? Rutherford postulated the presence of part neutral particle having actually mass comparable to proton but there was no direct experimental evidence.

Several theories and also experimental observations ultimately led the discovery of neutron. We can summarize some of the scientific monitorings behind the exploration of neutron.

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$$_4^9Be + _2^4α longrightarrow <_6^13C> longrightarrow <_6^12C> + _0^1n$$

Here the symbol  (_Z^XA) is provided where Z = atomic number and X = atom mass that the element A. 

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Figure 7. Ernest Rutherford (left) was awarded Nobel compensation in Chemistry in 1908 for his job-related in radioactivity. James Chadwick (on the right), a college student of Rutherford won Nobel compensation in Physics in 1935 for exploration of neutron.3

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Figure 8. The yellow foil experiment was originally conducted by Hans Geiger (left) and Ernest Marsden (right) under the supervision the Ernest Rutherford at the university of Manchester.4

What we have actually learned

Atomic mass = mass of protons + massive of neutron.For a neutral atom, number of proton=number the electron.Measured masses and also charges the the three elementary corpuscle are provided in the complying with table.
ParticleSymbolChargeMass
Electrone–-1.60×10-19 C9.1×10-31 kg
Protonp+  (H+)1.60×10-19 C1.672×10-27 kg
Neutronn00.00 C1.674×10-27 kg