Tag Info

Hot answers tagged

42

Why do most metals appear silver in color, with gold being an exception? It is hardly surprising that the answer to this question relies heavily on quantum theory, but most people will be surprised to hear that the full answer brings relativistic considerations into the picture. So we are talking quantum relativistic effects. The quantum bit of the story ...


16

Yes, so far, 20 synthetic elements have been created, with atomic numbers 99 (Einsteinium) to 118 (Ununoctium). All these elements are unstable, with half-lives ranging from a year to a few milliseconds. You can find a list on wikipedia. These elements are produced in specialized nuclear reactors, by bombarding heavy elements like Uranium and Plutonium with ...


14

D electrons in metal allow optical transitions in the visible regime. Visible light can be absorbed by elements, having unbound valence electrons in d shell. So Chemistry: optical d->s$^2$ transition Iron [Ar] 3d$^6$ 4s$^2$ Tin [Kr] 4d$^{10}$ 5s$^2$ 5p (full d shell) Aluminium [Ne] 3s$^2$ 3p$^1$ (is a special case: no d valence electrons, but Aluminium ...


14

Iron is a "special" element because of its nuclear binding energy. The very basic idea is that when you fuse two light elements together, you get a heavier element plus energy. You can do this up to iron. Similarly, if you have a heavy element that undergoes fission and splits into two lighter elements, you also release energy. Down to iron. You can see ...


11

First of all, this is not true that noble gases do not form any compounds -- it can be done with some chemical tricks, usually using fluorine and some hell conditions. Yet, you don't need any chemistry to detect a new element -- helium was for instance first spotted in the sunlight spectrum. The isolation can also be made by physical means only; the most ...


7

The history is summed up in http://en.wikipedia.org/wiki/Noble_gas#History . The concept of noble gas emerged from the discovery of argon. As said by mpq, the first to be seen spectroscopically was Helium. Then Argon was detected as a component of the air less reactive than nitrogen (http://en.wikipedia.org/wiki/Argon#History ).


6

I think that you are asking whether there's an example of a naturally radioactive material, or an irradiated material, whose decay is quick enough that you can prepare a sample with one set of physical and chemical properties, wait a finite amount of time, and have a sample that is visibly changed. This would require you transform a chemically significant ...


5

The sun's spectrum is very complex, and indeed there are a lot of "lines" both light and dark (emission and absorption) amidst a sea of what looks to be continuous frequencies. Note that the atoms you study in a textbook are idealizations. In a hot object such as the sun, some photons come to us by way of atomic emissions, but the speeds of the atoms that ...


5

Gravity is not needed in any way (it only helps to increase the pressure inside the stars but the pressure may be "mimicked" in other ways) and the energy needed for these transmutations isn't extremely high. It's just the nuclear energy conditions. See https://en.wikipedia.org/wiki/Synthesis_of_precious_metals Consequently, one may produce gold in ...


5

I'm not sure whether this counts as an answer since it is just one more idea for a fraud, but your question is about the physics of alloying. Actually there's no need to alloy to scam. You make up the filler mostly with tungsten, but add a little pellet of platinum. Neither of these materials will rouse the authorities' suspicion, since both have ...


5

NO Near the big bang temperatures were high enough that nuclei were not important. The binding energies of nuclei were trivial compared to the temperature. There was a sea of (as currently understood) quarks and gluons, so nuclei may have formed for a short time, but would break apart immediately. The best understanding is that what came out was protons ...


4

In fact, some nuclear theorists do believe that there will be relatively stable heavy elements, as per your point 2. The so-called Island of Stability is predicted to occur because stability is maximized at certain so-called magic numbers which correspond to especially stable isotopes when the number of protons and/or neutrons matches one of the numbers. In ...


4

If by "currently" you mean right this second, then probably -- but we won't know until it works. But if you mean recently, and I'm sure people are working on more, then the answer is yes. If you look at this table, you'll see that the newest entry is 2010 for Ununseptium. So people are interested in creating new elements. As for why, my personal ...


3

Metallic hydrogen is a metal that's not found on earth (but may be present in Jupiter): http://en.wikipedia.org/wiki/Metallic_hydrogen Wether it does anything but evaporating or burning at ambient temperatures and pressures (or whatever conditions those aliens encountered in this movie), I don't know. Since metals a generally in the lower left corner of ...


3

Finding a radioactive item is conceptually the same as finding a light source. You detect what it emits with a sensor that measures the angle the radiation comes from and project it back. Do this with a few detectors and find the common point. The problem comes if you can only absorb the radiation without measuring the direction. What radiation is it ...


3

It's not easy. However there are attempts to calculate a phase diagram of an element from first principles. For example, in this paper http://prl.aps.org/abstract/PRL/v95/i18/e185701 the solid-liquid transition of diamond is calculated. The calculation of the free energies is done with ab initio molecular dynamics. This means that the carbon nuclei are ...


3

Protons are positively charged, and neutrons are neutral, so large nuclei are highly positively charged. A postively charged sphere will energetically prefer to break up into two separate charged droplets which move far apart, this reduces the electrostatic energy, since the electrostatic field does work during this process. This thing, spontaneous fission, ...


3

According to this site, we have about 433 working reactors, 65 under construction, 160 planned and 323 proposed which is too many... We're consuming about 67,990 tons per year of U-238 which would probably die out soon within about 75 years. Besides fission products, spent fuel rods contain some plutonium produced by the U-238 in breeder reactors by ...


3

That depends on what is meant by "solving" the atom. What Feynman probably is referring to is the usual atomic Hamiltonian, which is already an approximation from the field theoretic point of view (no strong forces, etc.). The main problem is electron-electron-interactions. If you have an atom with more than one electron, the interaction term between the ...


2

In physics, "mass" always refers to "rest mass". In some older books and unfortunately many high school level physics books, the concept of "relativistic mass" is introduced, which increases as a function of speed. But this is then nothing more than the total energy of the object, therefore a redundant concept. Now, the mass of an object is, as Einstein has ...


2

I think the plot you show is the estimated abundance of the interstellar medium from which the Sun has formed. The chemical abundances of the interstellar medium change with time, so you have to define some point in time at which to estimate them. As the initial chemical abundance in the Universe is basically H, He, with traces of D, Li and Be, then it ...


2

Certainly with a cloud chamber you can. Here is a nice video of using one: http://www.youtube.com/watch?v=Efgy1bV2aQo There are many instructions on the internet for making your own cloud chamber and observing decay of radioactive americium-241 from an ionizing smoke detector for example.


2

Rather than write something unintelligible, I'll quote from a page on cesium clocks. According to quantum theory, atoms can only exist in certain discrete ("quantized") energy states depending on what orbits about their nuclei are occupied by their electrons. Different transitions are possible; those in question refer to a change in the electron and ...


2

Transuranic elements are typically unstable with respect to both alpha decay and spontaneous fission. The log of the half-life for alpha decay varies approximately linearly with $E^{-1/2}$, where $E$ is the energy of the alpha. If you know the binding energies of the parent and daughter nuclei, then you can calculate $E$ from conservation of energy. ...


2

The Balmer series for hydrogen is an example with some visible lines, and some lines outside the visible spectrum. On the other hand, the Lyman series for hydrogen is completely outside the visible spectrum. Since every element has an infinite number of spectral lines, it would instead be very unlucky if they all somehow fell outside the visible spectrum.


2

The estimated fraction of lead atoms in the universe is $6 \times 10^{−11}$.



Only top voted, non community-wiki answers of a minimum length are eligible