Discovery that Electron

Who found the electron?

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

You are watching: When j. j. thomson discovered the electron, what physical property of the electron did he measure?

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

What is cathode ray?

J. J. Thomson constructed a glass tube which was partly evacuated i.e. Lot of the air to be pumped the end of the tube. Then he applied a high electric voltage between two electrodes in ~ either end of the tube. He detected that a stream of fragment (ray) was coming out from the negatively charged electrode (cathode) come positively charged electrode (anode). This ray is called cathode ray and the whole building and construction is called cathode beam tube. The schematic the a cathode ray tube is given in figure 2.

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Figure 2. Cathode ray tube

Properties the cathode beam particle

1. They travel in directly lines.

2. They room independent of the product composition of the cathode.

3. Using electric field in the route of cathode beam deflects the ray in the direction of positively fee plate. For this reason cathode ray is composed of negatively charged particles.

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Figure 3. Deflection the cathode rays towards positively charged plates

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

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

The cathode ray bit turned out to it is in 2000 times lighter 보다 hydrogen.

Although we got e/m ratio for electron indigenous J.J. Thomson’s Cathode ray Tube experiment, we still don’t understand the exact charge (e) for electron. American physicist Robert Millikan design an experiment to measure the absolute value of the charge of electron i beg your pardon is disputed below.


Millikan Oil autumn Experiment

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Figure 4. Robert Millikan uncovered charge that electron and also won Noble prize in physics in 1923.2

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

Using the measured charge of electron, we deserve to calculate the mass of electron from e/m ratio given by J. J. Thomson’s cathode ray 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 actually learned

Electron was found by J. J. Thomson in Cathode ray Tube (CRT) experiment.Electrons room negatively charged particles through charge-to-mass proportion (-1.76×10^8) C/gmThe fee of one electron to be measured by R. Millikan in Oil drop experiment.Charge of one electron is (-1.60×10^-19) CMass of one electron is (9.1×10^-28) gram.Electron is around (2000) time lighter 보다 hydrogen.

Discovery that Proton
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Figure 5. Schematic yellow foil experiment

In 1909, Rutherford uncovered proton in his famous gold silver paper experiment.

Gold foil Experiment

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

Results

Most the the corpuscle pass v the silver paper without any kind of deflection.Some that the alpha particles direction at little angle.Very few even bounce earlier (1 in 20,000).

Conclusion

Based top top his observations, Rutherford suggest the following structural functions of an atom:


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

Discovery the Neutron

From the ahead discussion, we have the right to see that the gold foil experiment offered a clear photo of the framework of an atom which consists of proton (nucleus) and also same variety of electrons external of the nucleus.

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Figure 6. Schematic diagram for the experiment that led to the exploration of neutron by Chadwick. $$_4^9Be + _2^4α longrightarrow <_6^13C> longrightarrow <_6^12C> + _0^1n$$But scientists soon realized that the atom model offered by Rutherford is no complete. Assorted experiments confirmed that mass of the cell core is about twice 보다 the number of proton. What is the beginning of this extr mass? Rutherford postulated the presence of some neutral particle having actually mass comparable to proton yet there was no direct experimental evidence.

Several theories and experimental observations ultimately led the discovery of neutron. We deserve to summarize few of the scientific observations behind the exploration of neutron.

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

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

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Figure 7. Ernest Rutherford (left) was awarded Nobel prize in Chemistry in 1908 because that his work in radioactivity. James Chadwick (on the right), a student of Rutherford winner Nobel compensation in Physics in 1935 for discovery of neutron.3

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

What we have learned

Atomic fixed = massive of proton + massive of neutron.For a neutral atom, number of proton=number of electron.Measured masses and also charges the the three elementary particles are offered in the following 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