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evil
12-06-2007, 09:29
This seemed to be the best place after the other sciencey threads.

Anyway, what differentiates one element from another? Is it simply the lay out of electrons, protons and neutrons?

Pertinax
12-06-2007, 09:30
It's the number of protons in the atom. This number is also the atomic number of the element.

Total number of neutrons can vary (isotopes), as can the number of electrons (ions).

evil
12-06-2007, 09:57
As simple as that?
So, assuming I understand this right, Carbon has 6 protons and Nitrogen has 7. This one extra proton makes all the difference between the physical properties, this one extra proton turns carbon, a solid at room temp, to nitrogen, a gas at room temp?

Xisor
12-06-2007, 10:05
As simple as that?
So, assuming I understand this right, Carbon has 6 protons and Nitrogen has 7. This one extra proton makes all the difference between the physical properties, this one extra proton turns carbon, a solid at room temp, to nitrogen, a gas at room temp?

No. But it does distinguish between them. Having additional neutrons (isotopes of an element, eg same protons, but different neutrons) can lead to an element displaying very different properties. A very obvious one is becoming unstable (and thus radioactive).

Similarly, in that vein, stable (or more temporarily stable) elements come with a certain combination of protons, neutrons and electrons (incidentally, it's possible to form things like anti-nitrogen using antiparticles), and it is these that determine the form of elements. It should be noted that there are isocores (same mass number different atomic numbers) that can have different numbers of protons (hence being different elements) but that still display similar properties.

It's an odd and complex topic, but in terms of what defines an element, it is just the proton (atomic) number.

Sojourner
12-06-2007, 10:06
It tends to be the electron content that determines an atom's chemistry - but the number of electrons that will sit in an atom's orbitals is determined by how many protons in its nucleus. The way the electrons interact determines how the atoms bond to one another, how reactive it is, pretty much all of its unique properties.

Steel_Legion
12-06-2007, 11:34
What I dont get is how sat Helium (4,2) is so different from a nearly identical atom, Luthium in terms of size (6,3 for Li?) Yet one is innert, the other very reactive and dangerous... how! One is a gas, the other a metal, when for example oxygen technically weights more than Lithium (16,8? I think that is wrong, but you get the idea) yet lithium is not a gas until very high temperatures

IG88
12-06-2007, 12:01
That has to do with the family the elements come in (the columns on the Periodic table). Helium's in a family of inert (non-reactive) gases, while lithium is an alkali metal. Yes, it is very weird and makes basically no sense.

Scythe
12-06-2007, 12:08
Helium is a very stable atom, a so called noble gass, which rarely reacts with other atoms. This is because the particular 2 electron configuration is extremely stable. The two electrons complete the 'first layer', and each atom strifes to have a stable outer layer, either by sharing or losing/gaining electrons. Helium, as a noble gass, doesn't need to do this, as it is already stable by nature.

On the other hand, Lithium is so reactive because it is so close to stable state. The atom is perpared to give up its 3rd electron really easily, as this allows the outer layer of Lithium to become stable. That is why Lithium is so reactive. It is classified as a metal, as all metals give away their electrons (while elements like oxygen try to absorb more electrons).

That's from my (rusty) chemical knowledge...

ow, and atom mass does not equal density. Wether an elements is liquid, gass or solid at a certain temperature, is also determined by the type of bonding between different atoms. Oxygen, for example, forms molecules of 2 oxygen atoms, while Lithium forms into a metal 'roster', which can consist of thousands of atoms.

El_Machinae
12-06-2007, 12:35
I think it's great that you're so curious about this topic. Chemistry is really easy once you figure it out, it's like math. You'll look at old chemistry problems and question how you even had trouble with the concepts.

I found that it's a visual jig-saw puzzle, especially when doing organic chemistry. Understanding electronegativity is the key to predicting reactions.

raged_norm
12-06-2007, 14:21
Basically what they all said,

The odd arrangement of the periodic table is no accident as it allows (relatively) easy prediction of reactivities and proporties (particulary the f-block, teh bit accross the bottom). Bear in mind that, as Sojourner said, the electrons tend to decide the chemistry of an atom as opposed to the protons which decide the element.

The actual stabilities of various elements more to with quantum states within the electron shells (every noble gas has a full electron shell and is therefore stable), with more 'space' to accommodate more electrons the lower in the periodic table. Unfortunately the full treatment of this is beyond my knowledge/memory although I could dig out a book to refresh what I know if you're interested. It is enough to say that, reading the periodic table like a book, the closer to the noble gases you are the more reactive the element is.

Particular interest should be extended to the d-block (the bit of the periodic table), as these contain so many electrons that several stable states are accessible to them, as they bind to elements with different strengths depending on how many electrons they have. As such they find uses in many commercial applications because of this. The most well known is perhaps the use in cars for catalytic converters in exhaust fumes to convert nitrous oxide and carbon dioxide into nitrogen and water and other less harmful gases.

If you want to know more try this site (http://www.webelements.com/), it contains a wealth of information about the elements, or just ask me and I'll do my best.

I just feel the need to explain my credentials so you don't think I'm just being an internet know-it-all. I've just completed a masters degree in chemistry at University of Sheffield, UK and will be starting postdoctoral research work at the same institution in the autumn. I wont however to profess to know everything.

Steven

Corrupt
12-06-2007, 16:01
It's the number of protons in the atom. This number is also the atomic number of the element.

Total number of neutrons can vary (isotopes), as can the number of electrons (ions).

Yeah
Eg Hydrogen has 1 Proton, Helium has 2 etcetcetc
Other things dont reeeally matter (eg Carbon 13, Carbon 12, both carbon)
Well to elements being elements anyways, they change reactivity.
Basically the simple way is electron shells
Arranged 2,8,8 etc (I know its actualy 1s2, 2s2, 2p6, 3s2 etc)
Anyways if you have a full outer shell ur awesome and unreactive
If you need to lose electrons to gain an outer shell, or gain some, then you are more reactive.
The number of shells plays a part too.
Eg Potassium has 3 full shells preventing the positive nucleus attracting the negative outer electron. So it loses this more easily than lithium can and is more reactive

Corrupt
12-06-2007, 16:27
Edit: Corrupt beat me to it.

Heh
But your description was so much more eloquent than my recalling last terms notes in about 7 seconds

raged_norm
12-06-2007, 16:32
Wow, Corrupt and Netpixie are eloquent...

they explain it much better than me