Do You Think Our View of the Atom Will Every Change Again?

I love this story. Information technology is a story of how ideas changed about the nature of the atom. These are the notes (and diagrams) I employ when I teach the atomic nature of matter to non-science majors. The best thing about this story is that it is a dandy example of science. Science (or scientists) build a model. If new evidence comes along, the model gets changed. There are several other websites that describe all of this stuff, I volition list a couple at the end of this post.

Typical textbook model of an atom

Look in an intro, non-science majors textbook and you will probably see a picture like this of the atom. This model has some good ideas in information technology, just overall it has some bug. The key (and non incorrect points) of this model are:

• The atom is fabricated of protons, neutrons and electrons
• Almost of the space is taken upwardly by the area where the electrons be
• The protons and neutrons are in the core of the cantlet - called the nucleus

Greek Model of the Atom

It ever has to get back to the Greeks, doesn't it? Well, they did practice a lot of stuff. I know they were really scientists only it is however a practiced place to start. Hither is a pic of bosom of Democritus.

In real life, he probably had color. Democritus is credited with coming up with the atom. The question was, what would happen if you keep taking something (similar a tree) and breaking into smaller and smaller pieces? Would it always exist a slice of a tree? Could you go on breaking it into smaller and smaller pieces? Democritus said that if you keep breaking it downwardly, you would get to a size that could no longer exist broken. This would be the indivisible piece. In Greek, atomos = indivisible. Thus, the atom. (I know there is more to the Greeks, only I demand a place to start)

Dalton'southward Model

I am not going to get into the experimental show for Dalton's model of the atom, information technology's good stuff though. Allow me simply state what Dalton said:

• Stuff can exist cleaved into elements (the things listed on the periodic tabular array).
• Elements are atoms with different masses.
• Compounds are a combinations of elements. Y'all know, like water, salt or pizza.

Basically, Dalton just expanded on the Greek idea of the cantlet. An atom is a small things, and there are different masses with unlike properties.

J. Jonah Jameson Thomson - (AKA J.J.)

Thomson played with cathode rays. These are just beams of electrons (merely cathode ray sounds cooler). By having the beam collaborate with electric and magnetic fields, Thomson was able to determine the mass to charge ratio for an electron. So, from that he knew that the electron came from the atom, it had a negative charge and a pocket-size mass. Here is the model that he proposed.

Thomson took the idea of the atom and tried to comprise the evidence for the electron. In this model, the electrons are the small things and the rest of the stuff is some positive thing. This is commonly called the plumb pudding model considering the electrons are like things in positive pudding.

Rutherford Scattering

Ernest Rutherford said one day "hey, I recall I volition shoot some stuff at atoms." I am sure his wife said "oh, Ernie" (she probably chosen him Ernie) "if information technology makes you happy to play with your little physics stuff, go alee. I know how much you like information technology." Then he did. He shot some blastoff particles (which are really but the nucleus of a helium atom) at some really sparse aureate foil. Here is a diagram of his experiment.

If you lot shoot these positive alpha particles at this positive pudding atom, they should mostly bounciness off, right? Well, that is not what happened. Rutherford found that nearly of them went right through the foil. Some of them did bounce back. How could that be if the plumb pudding model was correct? Rutherford's experiment prompted a change in the atomic model. If the positive alpha particles mostly passed through the foil, merely some bounced dorsum. AND if they already knew that the electron was minor and negative, then the atom must have a small positive nucleus with the electrons around them.

Bohr Model

The model proposed past Niels Bohr is the one that you will see in a lot of introductory scientific discipline texts. At that place are a lot of good ideas in this model, but it is not the one that agrees with all of the electric current show. The model tries to brand a connection between light and atoms.

Suppose yous have some light and yous permit dissimilar colors bend different amounts (think rainbow). This way, you could come across what colors are nowadays for different lite sources. Here are iii different light sources.

Peradventure the light from the light bulb is what you would expect. These are the colors of the rainbow. Nevertheless, suppose yous took some hydrogen gas and excited it. In that location would only be certain colors (only certain wavelengths) of calorie-free produced. If you shine light through some hydrogen gas, there will be dark bands of low-cal at those same colors.

So, Bohr said that these colors of light in the hydrogen gas stand for to unlike energy levels the electron in hydrogen can have. And this is the primal to the Bohr model - electrons can ONLY exist at certain energy levels in the cantlet. This is crazy (at least it was crazy for its time). Think well-nigh a planet orbiting the Dominicus. It can be at whatever energy level. In this case, in that location is a gravitational force attracting the planet which produces orbital motion. This volition work anywhere in the solar organization.

Early physicist thought of the electron in an atom a lot like a planet orbiting the Sun. The central difference is that the electron (in the Bohr model) orbits due to an electric interaction and not a gravitational interaction. Well, the other departure in the Bohr model is that the electron tin can not orbit (if information technology does orbit, which it doesn't) at any distance and whatsoever free energy. Here is the essence of the Bohr model.

The Bohr model depends on a connexion between the frequency of light and the free energy of the level change. If light of a frequency respective to the free energy alter interacts with the atom, the electron tin can absorb the light and jump up a level. If an excited electron jumps downwardly a level, information technology looses energy. The energy the electron loses becomes light with a frequency corresponding to a the change in free energy.

The Bohr model tin can be quite confusing to introductory students, but the important point is that this model agrees with the following evidence.

• Electrons are small and negatively charged
• Protons are in the nucleus with is small compared to the size of the atom
• For a detail element, only certain frequencies (colors) of light are absorbed or emitted.

Schrodinger and Heisenberg Model

In that location is a key point almost the Bohr model that is no longer accepted in current models of the atom. In the Bohr model, the electrons are still thought to orbit the nucleus but like planets orbit the dominicus. Actually, this is something that we tin not say is true. The problem with atoms and electrons is that we humans except them to obey the aforementioned rules as things like baseballs and planets. Actually, the rules are the aforementioned, but baseballs and planets follow the rules of quantum mechanics without us humans even noticing.

It turns out that we can't really say anything almost the trajectory or position of electrons in an atom. What we tin can say is all nearly probabilities. We can say what regions an electron is likely to be. Here is a diagram that might assistance. These are probability distributions for the different free energy levels in an atom (from wikipedia)

Summary

Scientists build models. When new evidence is nerveless, the models change.

Links

• History of the Cantlet - this is some old page that has some cleaved images, but information technology is however expert stuff
• University of Colorado'southward Physics 2000 - over again, erstwhile, but skilful (if not a little dizzy)
• Physlet Bohr model
• Tutorial on atoms
• Wikipedia - Democritus
• Wikipedia - J.J. Thomson
• Wikipedia - Ernest Rutherford
• Wikipedia - Niels Bohr

Update:

I totally forgot that I fabricated a video lecture for this same stuff. If you like to listen and lookout instead of read, bank check this out.

Thing and Atoms from Rhett Allain on Vimeo.

Also, there is a great book on the history of the atom. History of Physics by Isaac Asimov. I highly recommend that book, even though it is no longer in print. I found my copy at a used book store.

karcherwuzze1991.blogspot.com

Source: https://www.wired.com/2009/09/the-development-of-the-atomic-model/

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