It is a story of how principles changed around the nature the the atom. These room the note (and diagrams) ns use when I teach the atomic nature of issue to non-science majors. The finest thing about this story is that it is a great example the science. Science (or scientists) construct a model. If brand-new evidence come along, the model gets changed.

You are watching: Which best describes the current model of the atom?


I love this story. The is a story the how ideas changed about the nature the the atom. These space the note (and diagrams) i use as soon as I teach the atom nature of issue to non-science majors. The finest thing about this story is the it is a an excellent example the science. Science (or scientists) construct a model. If brand-new evidence comes along, the model gets changed. There space several other websites the describe every one of this stuff, I will certainly list a pair at the end of this post.


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Look in one intro, non-science majors textbook and also you will more than likely see a picture like this that the atom. This model has some great ideas in it, but as whole it has actually some problems. The vital (and not incorrect points) that this version are:


The atom is made of protons, neutrons and electronsMost of the room is taken up by the area where the electron existThe protons and also neutrons are in the core of the atom - called the nucleus

It always has to go ago to the Greeks, doesn't it? Well, castle did execute a the majority of stuff. I understand they were really scientists however it is still a an excellent place come start. Right here is a photo of bust the Democritus.


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In genuine life, that probably had color. Democritus is attributed with coming up with the atom. The inquiry was, what would happen if you keep taking miscellaneous (like a tree) and also breaking into smaller and also smaller pieces? would it constantly be a piece of a tree? could you store breaking it into smaller and smaller pieces? Democritus said that if you store breaking that down, friend would acquire to a size that could no longer be broken. This would be the indivisible piece. In Greek, atomos = indivisible. Thus, the atom. (I understand there is more to the Greeks, yet I require a place to start)


Dalton's Model

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I am no going to go into the experimental proof for Dalton's design of the atom, it's good stuff though. Let me just state what Dalton said:


Stuff deserve to be broken into aspects (the things detailed on the routine table).Elements are atoms with different masses.Compounds are a combine of elements. You know, favor water, salt or pizza.

Basically, Dalton just increased on the Greek idea the the atom. An atom is a little things, and also there are different masses with different properties.


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

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Thomson played through cathode rays. This are just beams of electrons (but cathode beam sounds cooler). By having actually the beam connect with electric and magnetic fields, Thomson to be able to determine the mass to charge ratio for one electron. So, from that he knew the the electron came from the atom, it had a negative charge and also a small mass. Right here is the model that that proposed.

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Thomson take it the idea the the atom and tried to incorporate the evidence for the electron. In this model, the electrons are the small things and the remainder of the ingredient is some optimistic matter. This is typically called the plumb pudding model due to the fact that the electron are choose things in positive pudding.


Rutherford Scattering

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Ernest Rutherford said one day "hey, ns think I will certainly shoot part stuff in ~ atoms." ns am certain his wife claimed "oh, Ernie" (she probably referred to as him Ernie) "if it makes you happy come play with your tiny physics stuff, walk ahead. I know just how much you prefer it." so he did. That shot part alpha particles (which space really just the cell core of a helium atom) at part really thin gold foil. Here is a chart of his experiment.


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If girlfriend shoot these confident alpha particles at this optimistic pudding atom, lock should mainly bounce off, right? Well, that is not what happened. Rutherford uncovered that most of castle went right through the foil. Several of them go bounce back. How might that be if the plumb pudding version was correct? Rutherford's experiment motivated a readjust in the atomic model. If the hopeful alpha particles mostly passed with the foil, but some bounced back. And if they currently knew the the electron was small and negative, then the atom must have actually a tiny positive nucleus through the electrons roughly them.


Bohr Model

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The version proposed by Niels Bohr is the one that you will see in a many introductory science texts. There space a many of great ideas in this model, but it is not the one that agrees with every one of the current evidence. The model tries to make a connection between light and also atoms.

Suppose girlfriend take part light and you let various colors bending different quantities (think rainbow). This way, you might see what color are existing for different light sources. Below are three different light sources.

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Maybe the irradiate from the light pear is what you would certainly expect. These space the colors of the rainbow. However, mean you took some hydrogen gas and also excited it. Over there would just be specific colors (only certain wavelengths) of irradiate produced. If you shine light v some hydrogen gas, there will be dark bands of irradiate at those very same colors.


So, Bohr said that these colors of irradiate in the hydrogen gas correspond to different energy level the electron in hydrogen deserve to have. And this is the crucial to the Bohr version - electrons have the right to ONLY be at certain energy levels in the atom. This is stunner (at least it to be crazy because that its time). Think about a planet orbiting the Sun. It have the right to be at any energy level. In this case, there is a gravitational force attracting the world which produces orbit motion. This will work anywhere in the solar system.

Early physicist assumed of the electron in one atom a lot prefer a planet orbiting the Sun. The crucial difference is the the electron (in the Bohr model) orbits because of an electrical interaction and also not a gravitational interaction. Well, the other distinction in the Bohr design is that the electron can not orbit (if the does orbit, which it doesn't) at any distance and any energy. Right here is the essence of the Bohr model.

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The Bohr model depends ~ above a connection between the frequency of light and also the power of the level change. If irradiate of a frequency matching to the energy adjust interacts with the atom, the electron deserve to absorb the light and jump up a level. If one excited electron jumps under a level, the looses energy. The energy the electron loser becomes light through a frequency matching to a the readjust in energy.

The Bohr model have the right to be fairly confusing to introduce students, yet the important suggest is the this model agrees with the complying with evidence.

Electrons are little and negative chargedProtons room in the nucleus through is small compared come the dimension of the atomFor a specific element, only specific frequencies (colors) of light are took in or emitted.
Schrodinger and Heisenberg Model

There is a vital point around the Bohr model that is no longer accepted in current models that the atom. In the Bohr model, the electrons space still assumed to orbit the nucleus just like planets orbit the sun. Actually, this is something that we have the right to not speak is true. The problem with atoms and also electrons is that us humans other than them to obey the exact same rules together things prefer baseballs and planets. Actually, the rules room the same, but baseballs and also planets monitor the rules of quantum mechanics without united state humans also noticing.

It turns out that we can't yes, really say anything around the trajectory or position of electron in an atom. What we can say is all around probabilities. We can say what areas an electron is most likely to be. Right here is a diagram that could help. These room probability distributions because that the various energy level in one atom (from wikipedia)

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Summary

Scientists construct models. When new evidence is collected, the models change.

See more: Why Did Mendeleev Leave Spaces In His Periodic Table, Chemistry Chapter 6


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Update:

I entirely forgot that i made a video lecture for this very same stuff. If you like to listen and also watch instead of read, examine this out.