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Hi! Thank you for helping me with my previous questions, I was wondering if you guys could give me some insight on the following.

We all know that electrons create tighter bonds between, or in, substances. Electrons are found in electricity, as a matter of fact, electricity, or an electric current, is basically a stream of electrons. So when talking about something like ionic or metallic bonds, if you were to pass an electric current throught a substance, most likely a metal like copper or metal foil or of some other sort, would that significantly increase the materials strenght? I have heard that metallic bonds do contribute to somethings strenght and many other things. If not, why? If so, could the phenomenon be controlled, for example, increasing or decreasing the additional strenght of the material by increasing or decreasing the electric current passing throught it? How could I produce this phenomenon in a safe experiment, how should it be designed? How significant would the increase in strength be given the metal, could I calculate that? Would I get the same results as passing electricity throught a material if I simply charged it with a given amount of electricity/electrons? What metal or other material would be the best to use? Is there someother was I could increase a materials strength besides this way?

Question Date: 2008-02-16
Answer 1:

In general, just passing a current through a metal will not change the strength of the metal. Metals contain "extra" electrons that get shared between the metal atoms, which are what causes them to be so strong and such good conductors. However, when there is a current running through a metal, these electrons will still be there, just moving very slowly.

This probably would not cause the strength of the material to change very much, if at all. However, passing an electrical current through a metal would probably indirectly cause the strength of the metal to decrease, due to the fact that the current will cause the metal to heat up. When most materials heat up, the bonds between the atoms can get weaker; this will cause them to lose strength.

An experiment to test this would not be too easy, since you would have to measure the strength of the material at the same time as you are running a current through it, which would be rather difficult.

Other way to possibly change the strength of a material would be to heat it up. As I mentioned earlier, heating the metal will cause it to become less strong. Additionally, if you heat the metal up, but then very rapidly cool it back down (by dunking it in cool water, for example), this could "lock in" the positions of the atoms, and possibly make it even stronger than it was to start. The only danger in this would be to be very careful when heating the metal up, since one could easily get burned.

Experiments to measure the strength of the material can be tricky. Since metals form such strong bonds, you would have to provide a lot of force to the object in order to see how easily it would break. However, if you used a smaller amount of metal, then it wouldn't be quite so strong to begin with, so it might be possible to measure its strength. For example, if you used a thin piece of metallic wire, you could hang weights from it and see how much weight it would take in order to break the wire. Then you could heat the metal up and try it again while the metal is still hot. Again, you'd want to be careful here since the metal will be hot and could burn you. After that, you could then try the method I mentioned above of heating the metal and rapidly cooling it and measuring its strength again.

There's a bit of information in this answer, but I hope it helped out!

Answer 2:

Passing current through or charging a typical metal like copper will not significantly alter its mechanical properties.In a metal, the Fermi level of electrons, which you can think of as a kind of average energy of electrons in the metal, is above the conduction band edge. This means that electrons are essentially shared throughout the material because electrons in the conduction band can respond freely to an applied electric field. These conduction electrons are not bound to a single atom, and adding charge to or subtracting charge from the metal will only raise or lower the Fermi level a bit. The conduction electrons do not contribute to the bonds of the atoms.

You should find that if the current density is high enough, the metal will become hot, increase its resistance, and lose some of itsstrength/rigidity. This is primarily a thermal effect since largecurrent means electrons in the metal scatter much more often and transfer kinetic energy to heat energy. The atoms in the hot metal move about more freely due to thermal energy, are less ordered, and make the metal less rigid. The metal also expands when heated. If you can find very thin wires, you could measure these thermal effects due to large current densities without having to apply much voltage. You'd need a multimeter and a means of applying tension to the wire to test its breaking point. A thermometer that you could clip to a point on the wire would be nice as well.

There are, however, piezoelectric and thermoelectric materials which do exhibit changes in material properties when one applies a voltageindependent of resistive heating. Piezoelectric expand or compress when a voltage is applied, while thermoelectric materials acquire a temperature gradient under an applied voltage. These sorts of materials are used commercially in many ways, but I am not sure if they are available in a useful form for a science experiment.

Answer 3:

What you are asking is basically the fundamentals of atomic quantum mechanics.

Electrons are present in atoms in what are called"orbitals", which are energy states that electrons exist in as part of an atom's structure. They are usually depicted graphically as electrons orbiting the atomic nucleus, much the same way that planets orbit a star. This isn't actually true, however; electrons exist as a probability wave distributed around the nucleus, in which the probability of encountering the electron at a given point in space is determined by this wave. The lower the energy state of the electron, the deeper the orbital and thus the more energy required to strip the electron from its atom.

When two atoms bond together, the electrons involved in the bonding form a new, bonding orbital that exists between the atoms being bonded. This orbital isat a lower energy state, meaning that it requires more energy to force the electrons out of it and break the bond. This is why covalent bonds are strong and make strong materials: the chemical bonds do not want to break, because it would require a lot of energy to pull the electrons out of their low-energy orbitals.

Electricity works like this: electrons in a high energy state or otherwise free, can leap from one atom to the next in the direction of the cathode. The electron needs to jump into an unoccupied orbital in the atom that it is going to, but in doing so, it leaves its own former orbital vacant, allowing another electron to come in and fill it. Thus, salt water conducts electricity well because it has ions that are electrically charged and can migrate through the fluid towards the appropriate electrode. Metal conducts electricity because the outermost electrons in a metal are in a semi-free state and there are plenty of vacancies in the outer, higher-energy orbitals that electrons can move in and out of. Last, plasmas are good conductors of electricity because the electrons have been stripped completely off of their atoms by the heat of the plasma, and consequently can go where they will.

Now, back to your question: what experiments can you do that will demonstrate this? I just said that heating causes electrons to become loose, ultimately becoming free if you heat it to the point where it ionizes and becomes a plasma. You can't heat it that much safely, but you certainly can heat substances and cause them to lose their strength: for example, frozen cheese isas hard as a rock, but if you heat it up, it will melt.

So, with that, here is the experiment: choose a substance that has a low melting point (as I said, cheese will do). Take strips of this substance, and insert a weight into one end of each strip, and add a hole to suspend the other end of the strip from across bar, a clothesline or something like that. After you have made the holes and attached the weights, stick some of your samples in the freezer, some in the refrigerator, keep some at room temperature, and heat some up in a Tupperware container that you immerse in warm water. When you are ready to do the experiment, attach them to your hanging line, and record how much they sag, and how quickly. Your hypothesis is that the ones you have heated will have had their electrons loosened by the heat, and so will not be as strong as the ones that you froze.

Answer 4:

Good questions! Let's back up a bit...

Electrons don't just create tighter bonds between substances; they are the reason why substances are held together. Every solid and every molecule is held together by electrons. Or to put it another way, electrons are what bond atoms to each other.

If an electron is tightly bonded between two atoms, it can't move. So it won't participate in electrical current, because it's stuck. Only electrons which are not tightly bonded can conduct electricity. We call the bonded electrons valence electrons. Each element has between 1 and 8 valence electrons. Most of the time an atom will try to fill a "shell" with 8 valence electrons, by using some of its own and by bonding to (or sharing electrons with) its neighbors. For example, oxygen has a valence of 6, and hydrogen has a valence of 1. So water (H-O-H) gives the oxygen atom in the middle a total of 8 valence electrons, including 2 that are shared with hydrogen.

Valence electrons, as I mentioned, usually don't conduct electricity, because they're bonded. In metals, there are additional electrons in each atom that are not tightly bonded to the atom, and these are free to move from one metal atom to the next. These "metallic" electrons don't contribute significantly to the strength of the material, which is mostly determined by valence electrons. So, passing current through a metal doesn't significantly change its strength.

There are two common exceptions, though. The first is temperature. The strength of many materials changes with temperature, and passing current is an easy way to increase temperature. There are some materials called shape metals or shape memory alloys which revert to their original shape when you heat them up.

The second exception is semiconductors like silicon. In silicon, it's possible to break a few of the bonds, which frees a few of the valence electrons (like 0.0001% of them). You can do this either by shining light on the silicon, or by adding impurities to the silicon which have extra electrons. Then the silicon can conduct electricity. But the strength of the silicon is not significantly reduced because 99.9999% of the electrons are still tightly bonded.

If you wanted to test the experiment, you could hang a milk jug from a ring, and hang the ring from some very thin piano or guitar wire, or some very fine steel wire, which you can buy in small spools from a hardware store. Wrap one end of the wire around a metal post which is screwed into solid wood. Now using a hose or watering pot, start filling the gallon jug until the wire breaks. Keep track of how much water you've put into the jug. Now, start over with new wire, but this time you add connections to a lantern battery (6V) or a stack of "D" size batteries. Use heavy wire to connect from the batteries to each end of the piano wire. (You can buy wire with alligator clips on it at an electronic store or hardware store.) Be careful, because the piano wire will get very hot, so you don't want to get burned, and you don't want it to touch anything that would melt or catch fire. Now with the wire hot, quickly fill the milk jug to the same level and see if the wire breaks. If it breaks sooner, then the wire has been made weaker by heating.

Anyway, that may be more than you wanted to know, but hopefully it gives you some ideas to play with!

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