Electron

Although major discoveries of the electron were made during the 19^th century the history of this particle and the atom goes all the way back to the 440 B.C.’s with the Greek Philosophers.

     Leucippus of Miletus and his pupil Democritus of Abdera were the first known people to come up with the idea of an atom. Although there original writings are lost information has been found through other philosophers of their time and from them we find that Leucippus and Democritus created 5 major points about the electron.

The first point states that all matter is made up of atoms and that atoms are the smallest particle of matter and these atoms make up everything.

     The reason that this theory was believed was because Leucippus believed that there has to be a particle which cannot be divided any more; the tiniest particle that everything is made up of, which to him was the atom.

     We got the name atom from Greek where “a” means not and “tomos” means cut, so the word atomos or atoms means uncuttable or indivisible.

     Democritus also reasoned that if matter could be divided infinitely, then all matter would be destroyed

     The Second point that was made stated that there is empty space between the atoms.

     Leucippus believed that if there was no void between the atoms then consequently the atoms would not be able to move however an unmovable substance could not make up all matter therefore there must be a space between the atoms.

     The third point is that atoms are completely solid, due to the fact that if there is a void inside an atom, the atom could be changed by its surroundings and disintegrate which would not make it an atom therefore the atom must be solid.

     The belief that Atoms had the same structure all through out was the 4^th point the Greeks came up with. The reason they believed this was because they also thought the atom was completely solid therefore it must have the same structure all the way around

     The final point states that atoms are different in their size, shape and weight.

This idea was severely opposed by Aristotle therefore this idea was pushed into the background for a long time to come

Although there were scientists who began looking back at the atom ever since 150 A.D. John Dalton was the first scientists who made a big impact on the atom.

John Dalton

     John Dalton is often called the father of the chemical atomic theory but, most of his work and ideas were new versions or often the same ideas as the early Greeks.

     Dalton believed that chemical elements are made up of atoms just how the Greeks had stated that all matter is mad up of atoms. Atoms of the same element have the same properties which goes back to the final point for the Greeks in saying the atoms are different shapes and sizes for different properties; this also explains the third point that Dalton believed, which was that atoms of different elements have different masses.

http://dbhs.wvusd.k12.ca.us/

Faraday was the next big scientist that came into the picture. In 1838 Faraday executed an experiment in which he took an electrostatic machine and when he ran an electric current through it, the tube had a glowing beam of purple light. But, Faraday noticed that between the cathode’s glow (negatively charged end) and the purple beam there was a dark space, and to this day that space is called, “Faraday’s Dark Space.”

     In 1831 Michael Faraday realized that by changing a magnetic field in a circuit also changed the magnetic field and voltage of a nearby circuit. Faraday made this discovery of electromagnetic induction with an experiment using two coils or wire wrapped around the opposing sides of a soft iron ring. The first coil on the right is attached to the battery. The second wire is attached to the compass.

When the switch is closed the compass moves for a second and then goes back to its original position, this shows that an electromagnetic force was induced making a current flow to the second coil for just a second however when you open the switch the compass’s needle moves for a second again but this time the other way.

When the switch is closed and opened the magnetic field in the ring changes by expanding and collapsing. These changes in the magnetic field could induce an electromotive force and current on a nearby circuit now the group of electromotive force and current is called electromagnetic induction.

http://micro.magnet.fsu.edu/electromag/electricity/inductance.html,

http://www.brooklyn.cuny.edu/bc/ahp/LAD/C3/C3_Electrons.html,

http://dbhs.wvusd.k12.ca.us/Chem-History/Faraday-electrochem.html.

(Above is James Clerk Maxwell)

A man by the name James Clerk Maxwell was interested in Faraday’s work and between 1864 and 1873 made his most important achievement of extending Faraday’s theories. Maxwell could show the behavior of the electrical and magnetic fields in a few relatively simple math equations, he also was able to calculate the speed of propagation in an electromagnetic field and realized that it was roughly the same speed as light. Maxwell also came up with the idea of the “ether” a term that was used to describe basically anything unknown (just like the term fluid) but it allowed scientists to converse more easily when talking about the unknown. Today we realize that all modern electronic devices are based on the math equations given by James Maxwell.

http://www.wsone.com/fecha/max.htm, http://inventors.about.com/library/inventors/bl_James_Maxwell.htm (picture as well), http://www.webstationone.com/fecha/max.htm

From Faraday’s day the vacuum suction pump that were used were not very well designed or handy causing many errors in lab results. But, Geissler a German glassblower was going to change all that. Not only did he develop a new and improved vacuum suction pump but he also was able to seal wires into the tube which were then attached to the metal electrodes making this tube the most efficient yet. In this tube you were also able to see the colors of the gas with electric current running through it. Many scientists such as Plucker and Crookes were indebted to this invention and Crookes even came up with an improved version of it.

http://www.brooklyn.cuny.edu/bc/ahp/LAD/C3/C3_Electrons.html, www.grammar.net.nz/dept_html

William Crookes made a new version of the Geissler pump in 1879 so; he could study cathode rays in more depth. He among others witnessed the affect of magnets on cathode rays, when a negatively charged object was brought near the ray, the ray repelled and when the ray was brought near a positively charged object the ray attracted. He also believed that the cathode rays were made up of negatively charged particles although he could not prove why this happened, there was no other answer as to why the ray bends when a negatively charged object is placed near it.

http://www.brooklyn.cuny.edu/bc/ahp/LAD/C3/C3_Electrons.html

At this time there was a split opinion as to whether a cathode ray was made up of particles or was an actual ray. People such as Hertz and Lenard believed it was a ray, and Varley and Crookes believed it was a particle. Also at this time Germany and Britain were arch enemies so the Germans tended to believe the cathode ray was a ray and the British believed it was a particle, but the irony here is that they are both correct.

Later on J.J. Thomson will be awarded in 1906 for a Nobel Prize in proving the electron is a particle and his son George Thomson will be awarded a Nobel Prize for showing it is a wave.

http://www.nuclearfiles.org/hitimeline/discovery.html

A German scientist named J. Plucker came around the same time that William Crookes did and executed almost the same experiment. With the Geissler tubes Plucker made great observations of electricity at low gas pressures, and in 1858 Plucker showed that cathode rays do indeed bend when in the presence of a magnet which helped to lead to the discovery of proving that cathode rays are produced in 1897 that cathode rays are made of negatively charged particles (electrons).

http://www.brooklyn.cuny.edu/bc/ahp/LAD/C3/C3_Electrons.html

One of J. Plucker’s students happened to be Eugene Goldstein, who accidentally came up with the name cathode rays. What E. Goldstein had noticed with his experiments using the Geissler tube was that the glow in the tube was coming from the cathode (negatively charged side) consequently he called it cathode rays. Since has was Plucker’s student he had also found that the rays could be moved using a magnet but, he also found out that these rays made a shadow of an object that was in it’s path proving that cathode rays also moved in straight lines.

If the cathode rays were, as Goldstein, believed made up of charged particles then they could be moved by a magnetic field as well as an electrical field, but as much as Goldstein attempted he could not show that the cathode rays bent when an electrical field was in its presence however it was a known and accepted fact that the rays bent in presence of a magnetic field and that could not be explained using the “ray” method.

With all of these new ideas popping up and many scientists had conflicting ideas support for their experiment or belief was key in making their discovery or idea important and C.F. Varley helped to make that happen. C. F. Varley never invented anything himself but he supported many people’s ideas and inventions even the ones that seemed unfathomable to the public he would support them and some of those unfathomable ideas actually turned out to be correct. His contribution was one of a catalyst; he sped up the process of discovery by support.

http://www.acmi.net.au/AIC/.html, www.vigyanprasar.com/

Heinrich Hertz is known for his great discovery of radio waves which he became immortal for by being given the unit hertz (which is one cycle per second), however Hertz also made contributions in the discovery of the electron by cathode rays. Hertz observed that the cathode rays were going right through a thin sheet of gold, and it seemed absolutely impossible that rays could travel through a solid, but then he conducted a second experiment which caused a big impact in the discovery of the electron. Hertz wrongly observed that the cathode rays did not bend in the presence of an electric field, this was an extremely toxic conclusion however Hertz was a famous and trusted scientist at the time consequently most people believed him to be true also because Goldstein also was not able to show that these rays bend in the presence of a electrical field. Hertz also believed that the cathode rays were like rays of light only shorter and this (wrong) experiment helped to prove his hypothesis true.

http://chem.ch.huji.ac.il/~eugeniik/history/hertz.htm,
http://www.chembio.uoguelph.ca/educmat/chm386/rudiment/tourclas/hertz.htm,

http://securehosts.com/fecha/hertz.htm

Phillip Lenard like Hertz did not believe Crookes when he said that he believed that cathode rays were made up of charged particles, but more like light waves. This belief was probably enforced due to the fact that Lenard was Hertz’s student but Lenard designed this experiment. He took a cathode ray tube and but a thin piece of foil at one end, the cathode rays went right through the foil and therefore could not be made up of charged particles because they would be deflected. After this experiment in Lenard’s mind there was no way to say cathode rays were charged particles. When information came out that the particles coming from the cathode were negative his response was that those charged particles had nothing to do with the glow therefore he still persisted in saying that the cathode rays were indeed waves.

www.dpgraph.com/

G. J. Stoney although he did not invent anything that impacted this discovery without him I would not be able to do this project because G. J. Stoney was the man who came up with the name electron. He proposed the name ‘electrine’ for the hydrogen atom’s unit charge but then in 1891 he changed the name to the same word we use today. The Electron.

www.vigyanprasar.com/, http://www.acmi.net.au/AIC/.html

In 1895 the split explanations of cathode rays between waves and particles was still in hot dispute, Jean-Baptiste Perrin believed that the rays were made up of particles and to prove it he designed a special cathode ray tube. This tube would allow the rays to be caught in a metal cylinder, since this was the object which was placed in the ray’s path. Then Perrin connected the cylinder to an electroscope (a device used to measure electric charge), the electroscope showed that the cylinder became negatively charged when the cathode rays went through it. This convinced Perrin that the rays were made up of negatively charged particles.

Since this idea was going against many well-known scientists beliefs there was a lot of objection the major one being that the  negatively charged particles might come from the cathode, but that does not mean that it is the same as the cathode rays.

http://www.acmi.net.au/AIC/.html, www.vigyanprasar.com/dream/

With all this uproar about these so called negatively charged particles sooner or later some one had to figure it out and that man was J. J. Thomson, however before I begin I would just like to say that although Thomson was a great scientist he did not do it alone. Many other scientists along the way fed into the ideas of Thomson and what he has executed therefore all the credit should not just go to him but to all of the other scientists as well.

He began by repeating Jean Perrin’s experiment by building a cathode ray tube which ended in two metal cylinders with a slit in them, he also found that these charges were negative but then he added a twist to the experiment. J. J. wanted to see if these charges could be separated from the cathode rays so he bent the rays with a magnet and now the cylinders held very little electric charge and from this observation he concluded that the negative charges and the cathode rays are indeed one and the same squashing the objection made during Perrin’s experiment.

Thomson believed that these cathode rays were indeed negatively charged particles, he also knew that if he could prove that the electric field as well as the magnetic field would bend the cathode rays then there would be no case for proving the rays were waves. Although Goldstein had tried to show this and Hertz had supposingly shown that the electrical field could not move the ray J. J. tried the experiment anyway, but he performed it in a new way. Thomson realized that a charged particle will bend as it moves through electric field but not if it is surrounded by a conductor so Thomson believed that the gas in the cathode tube was indeed a conductor to the cathode and so he painstakingly took nearly all the gas out of the tube. And he found that the rays did bend in the presence of an electrical field after all.

With these two experiments being proven there was no case to object to the idea that the cathode rays were charged particles therefore he boldly stated that this corpuscle was the substance from which everything is made of, the indivisible part. Thomson was not finished yet though he also came up with a third experiment in which he wanted to find out the basic properties of these corpuscles, since he could not measure the mass or electrical charge on a particle Thomson measured the angle of the bent ray and how much energy the ray carried, he received calculations from many different types of gases and tubes. From this generalized information he was able to create a ration or the mass of a particle to its electric charge (m/e).

After J.J. had proven the corpuscles he went back to the question he had been asking all along what were the basic properties of an atom, and so J. J. came up with a Plum Pudding model in which the pudding were positively charged particles and the plums were negatively charged. Since negative and positive particles attract they would stay in one place and J.J. just assumed there was a stable place inside the atom.

http://webserver.lemoyne.edu/faculty/, www.dpgraph.com/janine/ , http://dbhs,wvusd.k12.ca.us/

Fitzgerald played a tiny but pivotal role in this process by suggesting that J. J. Thomson’s corpuscles were the same as the Stoney electrons, bringing us to the name that we use today. http://www.acmi.net.au/AIC/.html

From 1897 onward with the help of J.J. Thomson’s work Rutherford was able to establish that electron had a charge 2,000 times greater than a hydrogen ion making the electron the lightest particle yet. The reason this was believed was because these particles were small enough to pass through solids and comparatively to the hydrogen ion which could not pass through solid matter it was proposed to be 2,000 times smaller.

Ernest Rutherford was extremely interested in alpha-particles and how they acted in fact he invented them and at that time they meant no more then very tiny particles. Ernest met up with Hans Geiger when he came back to England and also a man named Marsden. All three of these amazing scientists then witnessed the most dumbfounding experiment, the gold foil experiment.

A stream of alpha particles were sent to the gold, and most of the particles went right through as Thomson’s model shows us, however some of the particles were ricocheted of at a 90 degree angle or more. This astounded Rutherford! Later he said, “It was as though you have fired a 15-inch shell at a piece of tissue paper and it came back and hit you.”

From these observations Rutherford began to develop a theory about the scattering of these rays, he believed there is a charge concentration or as we call it the nucleus at the center of the atom. Since the nucleus is so small the tiny alpha particles have a lot of space in which they could go right through the atom. Some of the alpha particles by chance might come to close to the nucleus and be deflected a few degrees but the smallest amount of particles will hit the nucleus dead on causing them to be deflected off by 90 degrees or more. Since then no one has really challenged the shape and form of an atom. http://dbhs.wvusd.k12.ca.us, http://www.acmi.net.au/AIC/.html, www.vigyanprasar.com

Robert Millikan like J.J. Thomson made amazing discoveries which were not all his own, Millikan had the work of amazing scientists before him as something to lean on which aided him in making one of the greatest discoveries of the electron.

Robert A. Millikan was the first person to find the charge of an electron, the way he found the charge is not as complicated as we think.

Millikan became interested in the charge of the electron because it was one of the few things that J.J. Thomson had tried but, left unanswered therefore Millikan came up with a way to answer that question.

First an atomizer would spray a mist of oil drops, the reason oil was used was because it evaporated much slower and remained at a constant mass. Most of these oil drops were charged and occasionally one oil drop would fall through the pinhole.

If this drop was charged Millikan was able to stop it by passing voltage through the metal plates basically holding it in mid-air. This worked because the electrical charge encircling the drop was negative as well as the negatively charged plate below it and since the droplet was also charged and would repel the repulsion would cause it to remain in mid air. Once the electric current was stopped the oil drop would drop down because now there was no repulsion.

The simplified calculation Q=dmg or the charge of the oil drop (q)= the distance between the plates (d) times mass (m) of the drop times the acceleration due to gravity (g).

But, the problem was to be able to find the mass of such a tiny particle but this was made possible by measuring the terminal velocity. As a droplet moves through the air it accelerates which causes friction with the air molecules, by measuring the terminal velocity Millikan was able to find the mass by using the equation m= kv/g.

Using these equations Millikan realized that every time the answer was a multiple of  -1.62 x 10 -19 C, which today we know as the charge of the electron.

www.physchem.co.za/, http://dbhs.wvusd.k12.ca.us/

As we look back on to the Discovery of the Electron and find how much we have changed from believing that the atom is indivisible and homogenous, to the discovery of cathode rays, and proving the electron. Shows just how much science has progressed. This assignment also shows me why I believe in this so called particle, which now that I have researched it, I am quite surprised that no one in the text books have motioned these discoveries. I do believe that it is necessary to know all this background information on terms you use everyday, and if you do not know what it is you should find out. This paper helped me to do that and it brings not only an understanding of the electron but of cathode rays, Geissler tube, all the scientists, Milliken’s experiment. Even though all year you have said you should always know why things happen, never just because someone said so. It actually makes sense now, and now I truly do understand why we have an electron and not because anyone said so.

ok so i am officialy swamped with this whole buszka thang and i am so done with this xanga thing no one does it anymore...off to buszka!