Chemistry in the Playground

[Pyro]

So as the thread title says this is about chemistry. In my physical science class we are doing a unit on it, and the information on valence electrons is murky. I have a couple of questions about them and things in general below. Please answer them if you can...

What is the exact number of electrons each shell can hold? I've seen places say 2, 8, 18, ... or other that have 2, 8, 8, 18, 18...

Noble gases are often described as having full valence electron shells. Other sources describe them as have exactly eight valence electrons. Which description is most accurate of noble gases?

How many electrons make an atom stable? Does a full valence electron shell make it stable, or just having more than eight valence electrons?

Those are my three questions. Hopefully if I get good complete answers to them, everything else will fall into place. If anyone knows a chemist or university I can email, it would be greatly appreciated if you would PM me the contact details.

[Adlan]

Okay, What level of schooling are you talking about?

At GCSE, they taught me 2, then 8, then 8 then 8....

at A-levek, they taught me different.

I will be a chemist, but I'm not finished learning yet.

[Mr_Saturn]

I'm taking my first chemistry class this semester. Hopefully i'll learn somethig like that down the months.

[Ikkitosen]

For the number per shell...

Each shell has a principal quantum number, n. This can be defined as starting from 0 (sensible) or 1 (dumb). We'll use 0.

Each shell has a set of sub-shells, each with different orbital angular momentum, l. These values range from 0 to n, in integer steps. Each subshell contains 2(2l+1) electrons.

Each shell contains the sum of the number of electrons in its sub-shells.

So, starting from the innermost we have:

n=0. l=0 (the only possible value if n=0). 2(2l+1)=2. 2 electrons.

n=1. l=0 subshell. 2(2l+1)=2. 2 electrons.
l=1 subshell. 2(2l+1)=6. 6 electrons.

n=1 shell total = 6+2 = 8 electrons. Note the 2 possible values for l: 0 and 1, since n=1 and l can be any integer between 0 and n.

n=2 has l=0, 1, 2 with 2(2l+1) = 2, 6 and 10 electrons for a total of 18 electrons in the n=2 shell.

Stability is relative. A full sub-shell is pretty stable. A full shell is even more stable.

Oh, and this is atomic physics, not chemistry :smallamused:

[Monney Dhoo]

Sorry, I can't help you with the shell problem, I can't remember the chemistry from when I did A-level well enough to answer that, though it doesn't help that what I can remember is a more complex version of this stuff, which I learned from a physics degree.

But on the Nobel gases, they are stable because the outer (valance) shell is full. Helium for example is a stable Nobel gas with only two valance electrons. The exact number of electrons in the valance shell is irrelevant other than whether the shell is full. This applies for all atoms and governs the bonding within materials, and most properties of materials.

If the valance shell is more than half full the atom will want to gain electrons, while if the shell is less than half full it will donate electrons away, to be stable. This can be done in three ways, either by sharing some of the electrons in the outer shell with another atom which needs to gain electrons forming a valance bond.

This can also be done by receiving electrons from an atom that needs to get rid of electrons. This donation forms a positive and a negative ion which are then bound by electric attraction, this is ionic bonding.

The final type is when both atom need to donate electrons, so the electrons are released to form a 'sea' of electrons about the positive ion, with the attraction between the ions and the free electrons holding together the material. This is metallic bonding.

I could try to explain why it works that a full outer shell is more stable, but my understanding of it requires complicated physics that I barely understand after doing a degree in physics, so it would likely be more complicated than you would need and would likely contain concepts you will never come across unless you reach degree level.

[Wayril]

1. 2,8,8,18,18... etc. (this is based on sublevels given the names S, P, D, and F) I'll explain it in depth if you really care that much. (valence electrons go 2,8,8,8,8,8... because the d and f orbitals are really located between layers rather than on the outside.

2. Noble gases have filled s and p orbitals (ie. valence electrons), except helium because it does not have there are no 1p orbitals (so it only has 2 valence electrons), so the valence electron one is more accurate.

3. Stable isn't really a specific condition. That's like comparing lightbulbs and saying which one is bright. Well they're all bright, so the real question is which is brighter, or in this scenario, what is more stable. Filled octets/filled valence electrons, are the most stable, and the stability generally increases down the periodic table and to the right (Not entirely the situation, but for now that's accurate enough). So even noble gases can bond with other elements. (although it is usually induced in labs)

This is significantly easier to understand if you understand how the orbitals work, but I'd really rather not go into explaining that because it's not exactly a linear trend in the periodic table, as most other periodic qualities are.

[Pyro]

1. 2,8,8,18,18... etc. (this is based on sublevels given the names S, P, D, and F) I'll explain it in depth if you really care that much. (valence electrons go 2,8,8,8,8,8... because the d and f orbitals are really located between layers rather than on the outside.


Thanks so much! I finally get it (sorta). Not all the physics stuff, because thats way above what I'm learning. Just to make sure I have everything right in easy terms, I'll recap. Each valence shell can only have a maximum of 8 electrons. Each subshell can hold an X number of electrons. I think I got confused because I've been learning from books that add shells and subshells together, and that didn't always add up correctly. I think that'll satisfy me for now. This stuff is pretty interesting, maybe I should be a subatomic physicist.

EDIT: Nevermind, I decided I had another question.

Do atoms always have the same number of electrons as protons when uncombined, or does ionization only occur when atoms combine?

O and if anyone has more explanations for my first questions, keep them coming. I'm a bit obsessive about this I guess.

[ForzaFiori]

So as the thread title says this is about chemistry. In my physical science class we are doing a unit on it, and the information on valence electrons is murky. I have a couple of questions about them and things in general below. Please answer them if you can...

What is the exact number of electrons each shell can hold? I've seen places say 2, 8, 18, ... or other that have 2, 8, 8, 18, 18...
this is a confusing one. the first shell holds 2. the next one holds 8. after that, each shell of valence electrons is actually 3 sub shells of 2, 8, and 8. so each shell holds 18, and yet the outer one is 8.

Noble gases are often described as having full valence electron shells. Other sources describe them as have exactly eight valence electrons. Which description is most accurate of noble gases? Nobel gases have a full valence shell, be it a shell with 2 electrons, 8, or 18.

How many electrons make an atom stable? Does a full valence electron shell make it stable, or just having more than eight valence electrons? full outer shell

Those are my three questions. Hopefully if I get good complete answers to them, everything else will fall into place. If anyone knows a chemist or university I can email, it would be greatly appreciated if you would PM me the contact details.

hope that helps, my answers are in bold

[Ikkitosen]

I hated the fact that in chemistry they wouldn't explain why there were that many electron sin a shell or sub-shell. Physics is so much more...honest! Harder, but more honest.

Anyhow, the whole 2, 8, 8, 8 thing is a temporary stopgap until you learn better, but it may be all you need. It'll certainly help you figure out what's stable and why.

I'm glad you enjoy this stuff - bodes well for the future of science :smallsmile:

[The Prince of Cats]

I did love getting to A-level sciences and learning that things I took for granted were actually lies (they used the word 'models', but I call them lies) and respiration was actually a reaction that took six full sheets of A4 paper to describe, while electron shells were to do with quantum-physics and not just a collection of numbers to learn by rote...

By the way, 2,8,8,18,18... is not so hard: ignoring the first line, you are just dealing with squared numbers doubled (2*2*2, 2*3*3) and I seem to remember that pattern should continue (with the next lines being 2*4*4, which is 32, explaining the lanthanide and actinide anomalies)

My advice is not to think too hard about it. Just learn the pattern and remember that the only people who truly 'get' quantum physics are Oxbridge graduates and people who drop acid...

[Ikkitosen]

My advice is not to think too hard about it. Just learn the pattern and remember that the only people who truly 'get' quantum physics are Oxbridge graduates and people who drop acid...

I dislike this attitude* - although it makes us physicists seem like Very Clever People it also can frighten and discourage young people from entering the subject. I'm neither an Oxbridge graduate or someone who takes acid but I understand quantum physics. Couldn't do my job without it.





*This is nothing personal - your humourously delivered opinion is in fact very common. I see the effects of it after I answer the "So, what do you do?" question all too often. Physics is doable but a challenge, and you have to be a bit of a natural problem solver.

[Evil DM Mark3]

Speaking as a second year physics student at Plymouth University I can attest that what you have been told here is mostly, listen carfeuly, as true as you need it to be.

Learning scianece is a process of learning several layers of lies. Physics is the worst for that. The reason the valance thing isn't explained to you at A level or equivelant is that it is to do with Quantum Theory.

The biggest lie at university is the name of the course.

Biologists mostly study Bio-chemistry.
Chemists mostly study Atomic and Quantum Physics.
Physasists mostly study Mathematics.
A lot of Mathematicisans are in fact studing computing.
Computer sciance courses have a lot of robotics in them.
Robotics courses are, apparently, a mix of biology, marketing and phylosophy.

Oh and "If quantum theory doesn't shock, scare or utterly confuse you, you didn't understand it."

EDIT:Realised that no one had answered this:Do atoms always have the same number of electrons as protons when uncombined, or does ionization only occur when atoms combine?

An atom on its own in a total void will have the same number of electrons as protons and be uncharged. If it looses an electron it gains a posative charge, if it gains one it gains a negative charge. An ionic bond is basicly a pair (or more, but lets keep it simple) of atoms that have swapped (an) electron(s) over to give them full valance shells. This only occurs when the differance in valance electrons is high. An Ion can exist as a solid, eg salt. It can also exist as a liquid or disolved, there are millions of ions in a pint of water. A plasma is a form of ionised gas (not 100% correct but correct enough). So in short an ion can be in a compound, or loose on its own.

Confusing as it may seem atoms that can ionise to form ioic bonds are MORE stable if they lose or gain the elections, but are also MORE moblie and reactive in an electrical sence. Stability is relative, even noble gasses will form bonds if placed under enough preassure, although Helium is still somthing of a:smallfurious:.

[The Prince of Cats]

In all honesty, I studied Chemistry with an eye to Oxford, so I actually did 'get' quantum physics to some degree. It can be done, but it is not actually necessary for most people to understand quantum physics unless they actually intend to continue chemistry to degree-level. In many cases, the nature of quantum-physics can confuse you more than it helps to understand the underlying principals...

I told the physics teacher that the main lesson to be gleaned from Schrodinger's Cat was that someone should have called the RSPCA...

[Surfer99]

<snip>I told the physics teacher that the main lesson to be gleaned from Schrodinger's Cat was that someone should have called the RSPCA...

THAT i understand ! thats pretty much it too, disturbing thinking i actually got good grades in college level chemistry

oh well learning is good, using i remember more tho :P