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71

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

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 ...


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 ...


16

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 ...


14

The key to answering this question is the Goldschmidt classification of elements. Thirteen of the long-lived elements are siderophilic; they preferentially bind to iron. Those thirteen elements are significantly depleted in the Earth's crust compared to their prevalence on meteors, asteroids, and the Sun. This list of thirteen does includes rhenium to gold, ...


12

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 ...


9

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 ...


9

As John Rennie answered it very clearly, I would like to add some more details too. See, around early 1900 the idea of atoms was floating around the scientists' heads. At first everything was theory, but these things happened: You certainly heard of Joseph Thomson's cathode rays. Well, he actually calculated the ratio Q/m of atoms. (You can search any of ...


8

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 ).


7

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 ...


6

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

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

I don't have the rep to post this as a comment, so I'll give it as an answer. I should say that I am not necessarily in this field; I am an astrophysicist. I suspect that the idea of the Island of Stability is just a continuation of the early shell model for nuclei. This is basically a statement that nuclei with closed or filled energy shells are the most ...


5

The term "element" is reserved for atoms that have a nucleus that is a combinations of at least one proton and optionally one or more neutrons. Also, only a difference in the number of protons makes a nucleus considered that of a different element. Changing just the number of neutrons only makes a different isotope. Changing the number of electrons is ...


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 ...


5

Actually, they are still currently sinking to the core. Earth's internal heat comes from a number of sources, and one of these is the release of gravitational energy from the heavy elements migrating further toward the center. A similar statement holds for other planets. This isn't the majority of the source of heat. Other sources are the original thermal ...


5

There is no such experiment, though there are lots of experiments where the number of electrons in an atom are measured as a side effect. We know atoms are electrically neutral so there must be equal numbers of electrons and protons. We know successive elements in the periodic table are built up by incrementing the number of protons, so we know how many ...


5

Let me answer your second question first. A free neutron has a larger mass than a free proton (on the order of 1 MeV). An electron's mass is about half an MeV so it is energetically possible (meaning total energy is conserved) for a neutron to decay into a proton and an electron and still have enough energy left over to form an anti-neutrino (moving almost ...


5

This is one of the first examples of energy levels for electrons within the atom! If we take the Bohr model, which imagines that electrons circle the nucleus on set orbits Each of these orbits has a corresponding energy. The electrons are more stable at lower energy levels, and thus, prefer to be there. When you provide energy to the electrons (in the ...


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 ...


4

"iron magnets" are the regular kind of magnet. It's a rare-earth magnet, and the key ingredient in these is the rare earth metal. In this case, the Neodymium. One probably could replace the boron with something else and change the ratios a bit (probably getting a weaker but still effective magnet). The rare earth is what makes it so strong, so it is named ...


4

It also appeared to me that the higher you go, the harder it is to make an element. This is pretty much true. I have a tendency to be wordy and long in my posts, but I'll try to cover a few points as concise as possible. Ununoctium was created by "bombarding atoms of californium-249 with ions of calcium-48. This produced ununoctium-294, an ...


4

Yes, when you smash nuclei together it is possible to create other nuclei, including some that don't naturally occur because they are very unstable. Some of these other nuclides are created in particle accelerators while others are produced in reactors, when the fission of some elements can lead to an abundance of high-energy fragments that can combine with ...


3

Let's start with what "that thingy is X in colour" fundamentally means: You notice silver is not one of the colours here. However, silver is a LOT like white, as we will see in a second. There is another factor involved called specular vs diffuse reflection. White reflects all wavelengths diffusely (the reflected rays go every which way). Silver (e.g.,...



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