My biology book has a section about electron microscopes and it reads: "In an electron microscope, a beam of electrons- rather than a beam of light-produces an enlarged image of the specimen. Electron microscopes are much more powerful than light microscopes. Some electron microscopes can even show the *contours* of individual atoms in a specimen."
Then it goes on to define transmission and scanning electron microscopes.
Then it goes on to define transmission and scanning electron microscopes.
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Imagine I have an atom of carbon. It has a nucleus and a cloud of electrons orbiting around it. Now I take a second carbon atom and bring it close to the first. The outer electons reconfigure and are shared between both forming a carbon-carbon covalent bond.
If I look at the 'distribution' of those electrons I'd find that they spend 'most of their time' close to the carbon atoms rather than between them. In other words, over any given time period, the electric charge of those electrons is more concentrated near the carbon atoms than between them.
So if I was to look at that charge as a function of position, I'd see a bump near one carbon atom that decreases between them, and a bump again near the second carbon atom. It would look something like: UU .
This is what the electron microscope 'sees'. It works by firing electrons onto a surface, and looking at electrons that are scattered back from the surface. Obviously these probe electrons are more likely to be scattered back from regions near the carbon atoms than between them because the distribution of the electrons in the carbon chemical bonds is not uniform, and is more 'concentrated' near the carbon atoms.
If I look at the 'distribution' of those electrons I'd find that they spend 'most of their time' close to the carbon atoms rather than between them. In other words, over any given time period, the electric charge of those electrons is more concentrated near the carbon atoms than between them.
So if I was to look at that charge as a function of position, I'd see a bump near one carbon atom that decreases between them, and a bump again near the second carbon atom. It would look something like: UU .
This is what the electron microscope 'sees'. It works by firing electrons onto a surface, and looking at electrons that are scattered back from the surface. Obviously these probe electrons are more likely to be scattered back from regions near the carbon atoms than between them because the distribution of the electrons in the carbon chemical bonds is not uniform, and is more 'concentrated' near the carbon atoms.
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The uncertainty in the position of the electron is of the same order of magnitude as the diameter of the atom itself. As long as the electron is bound to the atom, we will not be able to say much more about its position than that it is in the atom. Certainly all models of the atom which describe the electron as a particle following a definite trajectory or orbit must be discarded.
We can obtain an energy and one or more wave functions for every value of n, the principal quantum number, by solving Schrödinger's equation for the hydrogen atom. A knowledge of the wave functions, or probability amplitudes yn, allows us to calculate the probability distributions for the electron in any given quantum level. When n = 1, the wave function and the derived probability function are independent of direction and depend only on the distance r between the electron and the nucleus. In Fig. 3-4, we plot both y1 and P1 versus r, showing the variation in these functions as the electron is moved further and further from the nucleus in any one direction. (These and all succeeding graphs are plotted in terms of the atomic unit of length, a0 = 0.529 ´ 10-8 cm.)
We can obtain an energy and one or more wave functions for every value of n, the principal quantum number, by solving Schrödinger's equation for the hydrogen atom. A knowledge of the wave functions, or probability amplitudes yn, allows us to calculate the probability distributions for the electron in any given quantum level. When n = 1, the wave function and the derived probability function are independent of direction and depend only on the distance r between the electron and the nucleus. In Fig. 3-4, we plot both y1 and P1 versus r, showing the variation in these functions as the electron is moved further and further from the nucleus in any one direction. (These and all succeeding graphs are plotted in terms of the atomic unit of length, a0 = 0.529 ´ 10-8 cm.)