Tag Info

Hot answers tagged

11

Yes, it is possible to predict the color of a substance, but it is, in some cases, very complex. The color of a substance is decided at various levels. The most "trivial" level is the molecule in gas phase. You have a molecule, all by itself, and when you send some white light on it you provide all the colors of the spectrum. The electronic configuration ...


8

It's not simply a matter of size. Generally nanoparticles are a few nm to 100 nm and most molecules are smaller. But, for example, single chain of a high molecular weight polymer or a DNA molecule can easily be much larger than 100 nm which would put it outside the conventional "nano" range. The distinction is somewhat fuzzy. Is a fullerene a molecule or a ...


7

It is just that the buckyball's faces are not holes as in popular view; there is pretty much electron probability density there forming quite a strong barrier. Also the size of the faces is comparable to the size of a, for instance, oxygen molecule, so I'm pretty sure that it is impossible for a buckyball to release a molecule just because of one atmosphere ...


7

This phenomenon is called phosphorescence. Electrons in the material are pushed into excited states by light, and then drop back down, emitting light with a characteristic frequency corresponding to the energy of the transition. It is analogous to fluorescence, however whereas fluorescence is a very rapid process, phosphorescence is delayed due to the ...


6

Some digging revealed the answer. It's called Triboluminescence. Basically, when certain materials are subjected to mechanical shock, chemical bonds are asymmetrically broken. This creates a charge separation, which on recombination ionizes the nitrogen in the air. Resnick-Halliday-Walker (in the Electric Field chapter--its the 'chapter conundrum-) states ...


6

ONE. This question is very speculative, so I don't think a specific and technical answer is available. Scientists are extremely hesitant to call anything impossible (including both silicon-based life and a conclusive answer to this question). Certainly no one has yet proven that life can't be based on silicon, and because it has the same number of valence ...


5

You have one 1s atomic orbital for each H atom, and one 1s, 2s and three 2p for each C. This makes a total of 36 atomic orbital in the whole molecule, and so you have 72 spin states. The 2s and 2p's orbitals are going to hibridate giving three 2sp$^2$ orbitals and one 2p orbital, so it has its characteristic $\pi$-delocalized electronic estructure on the ...


5

By conductor of heat, do you mean that it is bad at transferring heat via conduction? Or that it is just bad at transferring heat? First, a picture of the molecular structure of an oil: Conduction Oil is a liquid. Heat transfer by conduction requires strong bonds between the molecules, so that a vibration(heat) travels down the line. With liquids, this ...


5

It has to do with size. A molecule is in the range of picometers. A carbon-carbon bond is 154 picometers, so you expect most molecules to fall within the range 100-1000 picometers = 0.1 to 1 nanometers. A big molecule, such as a ribosome, or DNA, falls in the range of 10-1000 nanometers. Everything that falls in this range is "nano" by very nature. ...


5

A nanoparticle as typically used in nanotechnology refers to a particle with diameter on the order of 1-100 nanometers, or $10^{-9}$ to $10^{-7}$ meters. However, it's not just a matter of size. These particles are not typically "molecular" in the sense that they are not stoichiometric units made out of atoms held together by covalent bonds. Indeed, most ...


5

Argon is produced when Potassium 40 decays. The majority of Argon in Earth's atmosphere comes from this source. We know this because K-40 decay produces Ar-40, and the majority of Ar in the atmosphere is Ar-40. In the sun the majority is Ar-36. JR


5

Talking about (solid) metals as monoatomic or diatomic is somewhat tricky (solids are not like gasses), with discrete structures freely bouncing around. They are clumped together in large lattices, with each neighbour interacting with each other neighbour. In essence, something like a lump of gold is a N-atomic lattice of atoms.


4

It's important to note that color is only defined given knowledge of three things, see especially this section of the wikipedia article which has a nice discussion. 1) Light absorbing / reflecting properties of a material 2) Properties of the light source 3) Properties of the human perception of light In general, 1 is determined by the interaction of the ...


4

A good source of spectroscopic data is the NIST Chemistry WebBook. It compiles all possible information about polyatomic molecules including their UV/Vis and IR spectra. You will find references to corresponding papers and, as I see, the new version includes a Java applet that plots the UV spectrum. Here is a direct link to THT spectrum.


3

No, the autoprotolysis equation equilibrium makes the concentration of OH- to decrease appropriately. Say, the H3O+ is 1 mole/ltr, the OH- will be 10exp-14 moles per liter. If You calculate that precisely, You will find that the OH- and H3O+ will differ a tiny bit from that values. But compared to the deviations of the quilibrium due to temperature and ...


3

White phosphorus requires oxygen to burn. With oxygen, it will form an intermediate that can also react with water (to produce phosphoric acid). Ammonia also does not react with white phosphorus; in fact, it is used as a solvent for phosphorus-metal chemistry.


3

When one excites fluorescence with light (e.g. blue light), the incoming photon pushes an electron into a higher state. Generally one always excites vibrational states (movement of the molecules' atoms) as well. Therefore the emitted photon has lower energy (e.g. green light). The lost energy (internal conversion) heats the solvent or lattice. The shift in ...


3

Molecules don't know. Consider the following reaction as a template for some reaction that is favored to go in the direction indicated. \begin{align*} A-B +C \rightarrow A-C +B \end{align*} In a large collection of such molecules you can always find some $AB$ going to $AC$ and some going backwards. It is just that significantly more $AB$ are going to $AC$ so ...


2

Start of an answer... hoping someone else will edit / comment / improve. The reason that water expands on freezing is that the crystalline state has a specific orientation of the molecules (through hydrogen bonds) that leaves a lot of space between them. So where most of the time the liquid is a "messy form of the solid" and therefore takes more space, for ...


2

Manufactured 'lemon juices' such as cordials typically contain emulsifiers which can act as surfactants to lower the surface tension of the liquid. This would result in a foam forming more easily when air becomes 'trapped' during pouring water into the jug. Even homemade lemon squash which often has honey added as a sweetener will produce a foam because the ...


2

This is a chemical reaction that occurs when the strong citric acid in lemon juice reacts with the water(water acts as a base). To form methane among other gases. $$C_6H_8O_7 (acid) + H_2O(base) = CH_4 + others$$ (Not balanced). The reason why it does not foam as much whenever you pour slowly/closely is because you are not supplying enough energy for a ...


2

I too have seen this effect with pure, unsweetened lemon juice. To form a foam, (1) a surfactant is needed to lower the host liquid's surface tension (2) one needs to do mechanical work on the liquid to swell the surface area of the bubbles/foam and (3) the foam needs to be made faster than it breaks down. The Foam Wikipedia Page has a good summary of this. ...


2

The NIST Atomic Spectra Database is a decent source for general-purpose lookup and identification of spectral transitions and levels. You will probably be more interested in their spectral line info.


2

Ferromagnetism is the basic mechanism by which certain materials (such as iron) form permanent magnets, or are attracted to magnets. It is caused due to unpaired electrons alignment in same spin moment to create high value of magnetism. We cannot comment on spin moments of the electrons(unpaired) just by seeing , so i think it's not possible.


2

The answers you got on Chemistry are fine. Above the QFT level, physical systems find optima by a combination of randomness and asymmetric gradients. In this case the energy requirement for going from a prefered state to a less prefered one is higher than for the oposite reaction (which is roughly what is meant by "most stable" in the first place). At the ...


2

To understand this you need to start from the point there is no such thing as an irreversible reaction. As an example take some simple model gas phase reaction where A and B collide and the reaction forms C and D. The reagents A and B collide with at least the activation energy, react to form C and D, then the products C and D fly off with more energy than ...


2

So my question is actually twofold: how did people manage to discover them more than 100 years ago (historically), Historically there are many different ways people discovered different elements, and many ingenious ways of proving that they were actually elementary. One of the most useful and revolutionary was the discovery of Electrochemistry. Where ...


2

Polymer chains pack together more densely when they're more crystalline simply because they line up with each other better. It's the same reason a ball of string has a higher density than a random tangle of string. http://en.wikipedia.org/wiki/Crystallization_of_polymers has some info on this including examples of density for different crystallinities.



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