Physics or Chemistry Question?

[extropalopakettle]

I'm not sure whether this falls under physics or chemistry, but that's not the question.

Is there a general theory under which the physical properties of elements (color, melting point, hardness, etc) are explained given just the number of protons, electrons and neutrons of their atoms? Obviously we know these things empirically. For most of these things, we're talking about numerical quantities. Are there formulas or algorithms where you can input x and y (protons and neutrons) and get out z (melting point), without, of course, resorting to a table of empirically determined values.

Similarly for nuclear properties (half-life of radioactive isotopes).

[MatthewV]

I don't recall ever seeing property relations going back to the number of protons, electrons and neutrons of their atoms. I will review my material sciences book and get a proper answer.

There is a chance a relation exist for pure elements. Most of my classwork was about mixtures, alloys and compounds.

[Zag]

http://www.wou.edu/las/physci/ch412/perhist.htm

[Zahariel]

In principle, yes. I mean, nature does it somehow, right?

From the composition of the atoms (and a LOT of quantum physics) you can work out molecular bonding strengths, orbital energies, typical crystal structures and the kinds of flaws they can contain, values for intermolecular interactions (van der Waal's forces or London dispersion forces), and some other things.

The various molecular orbital energies tell you what wavelengths of light the substance will absorb, and thus what color it is, as well as properties like fluorescence or phosphorescence (normally molecular vibrational energy states are far too low-energy to interact with visible light, so only the orbital energy states really matter). The crystal structure and the bond strengths or intermolecular interaction strengths tell you the hardness, thermal conductivity, melting point, and some other things. The molecular or crystal structure determines the heat capacity, which is a function of the entropy of the molecule, which in turn is a function of the number of degrees of freedom it has. Certain aspects of the electron structure determine the electrical conductivity (although there are confounding factors there having to do with intermolecular forces). You can eventually (with a LOT of work) determine whatever it was you wanted to know.

For example, diamonds and most other gemstones are hard and extremely conductive (thermally) because they are purely crystals, with no intermolecular forces (because only one molecule); but many are brittle because a very tight crystal structure made of small atoms is extremely unforgiving of flaws and thus generally doesn't have any mobility. Softer crystals tend to have large voids (fluorite) or freely moving parts (calcite) in the crystal structure where impurities can more easily interfere. In steel, the carbon atoms in the iron force flaws in the crystals around which they can flex more easily (this is possible because carbon is smaller than iron, so it can slip into gaps while the crystal is forming). In graphite, each plane of carbon atoms is bound very tightly together (even more than diamond), but the planes are only bound to one another by London dispersion forces, which are comparatively very weak, so the planes can slide across one another easily (this is why graphite makes a good lubricant).

Nuclear properties are less predictable because we don't have accurate models of their behavior. The preceding discussion was valid only because we now (in the last roughly 30 years) have accurate quantum models of electronic behavior, which is necessary for a lot of the calculations. Some nuclear reactions are well understood, but why they have the values and half-lives they do is quite mysterious. The chemical discussion is about deriving the behavior of atoms and molecules from (observed) properties of their constituent parts. We haven't been able to observe properties of the constituent parts of the electrons, quarks, and gluons that control nuclear properties.

In practice, it's a lot easier to just observe the properties you wanted in the first place, unless you want to know (e.g.) chemical properties of atoms that decay too fast to manipulate them.

[Zag]

You've convinced me, Z, that the answer to the original question is no. Because without knowing more about a substance than its atomic makeup, you can't, for instance, distinguish graphite from diamond from soot. I know that diamond is not a stable form for Carbon at STP, it's just that it is an incredibly deep valley in its stability graph. It never actually breaks down at STP because no individual atom ever reaches enough energy to escape the structure. (I'm sure you can translate this into the proper terminology for me.)

Also, call home and get caught up on the latest. Sigh.

[Lepton*]

Just to agree... Broadly sorta, but specifically, no. Densities of the solid pure elements are relatively predictable, and you could probably put together a not-horrible formula to model the melting points of the metals based on their atomic numbers, but things like color -- and the non-metals -- are more difficult. The state of mercury and the color of gold are both things that aren't even explained by quantum mechanics: they rely on the addition of special relativity, as in quantum field theory or as a perturbation to quantum mechanics.

You could do a decent job of predicting the properties of ions with only a single electron, and thus the series {H, He+, Li2+, Be3+, B4+, C5+,...} could be so predicted. For example, you could find the energy gaps using a modified Rydberg formula. But it wouldn't be very useful...

[Johny01]

My answer is yes. Electron, proton and neutrons are there in an atom. But it’s not visible for us. Also this question is belongs chemistry.
_________________
Prams pushchairs and Britax are perfect gifts for new moms.

[MatthewV]

I like Zahariel's answer also. In theory, there is some system to how the world work. It could even be a time dependent solution-- what is to say the "color" of gold won't change in ten billion years?

From the engineering side, the answer is certainly No. Or at least Not Yet. We can predict some things such as color when band energies are known. But that is a few steps away from the fundamental side you seek.

[extro...*]

[Jack_Ian]

I know a large part of Crystallography involves ascertaining the crystalline structure given a substance's properties and vice versa, but Materials Science is probably what you're looking for.

The answer to your question about colour, involves the ability of a structure to absorb, reflect and generate energies. What colour something is depends upon what you shine at it. If a crystal is black in visible light, but yellow in ultraviolet light, then what colour is it? Is charcoal black or red? What if it's hot?

It gets quite involved, but a quick look on the internet pointed towards this which should get you started, if interested.