15 replies to this topic

[Infernity]

Hmmm, I know the electrons turn in circles around the nucleus, *fast* so he said.
What speed are we talking about?

Thanks

Yours truthfully
~Infernity

[armrha]

Well... not that fast, really.

Niels Bohr is the person responsible for the idea of electrons revolving around the center of an atom. An atom, unlike a planet or gravity well, only has specific paths at specific distances where electrons will revolve. As you know, nuclei are positive and electrons are negative, so they have to move, and as it turns out, the fastest a hydrogen atom's electron will be moving is at 220,000 miles per hour. As the atoms get larger, and the more electrons you have, they fill up shells and move further out, and move slower and slower, not needing to move so fast in order to escape the attraction from the center.

That puts them moving at under one percent of the speed of light: Pretty slow, as far as things go. Electrons in transmission move close to the speed of light, actually at some points faster and some points slower, but always on average lower...

[Infernity]

220,000 miles per hour, shall be 354,055.68 kilometers per hour. Wew thanks!!
Another question pretty related, how come Pd (palladium) has 18 electrons in the external layer? It should not be more than 8, and Pd has 18!

Thank you

Yours truthfully
~Infernity

[stormheller]

Because it goes 2, 8, 18, 18 (etc) and Pd has 4 energy levels filled.

[Infernity]

Mmm I heard something about it, can you explain me more please?

I know that for atoms to gather in order to become a molecule, each atom is trying to complete himself to have 8 electrons in the outside layer of electrons.

Can you or make me a short explanation about all this?

Thanks

-Infernity

[jaydfox]

220,000 miles per hour

It's been a while since I've seen the equations, so I might be misremembering, but I thought the orbital speed of an electron (in the lowest energy state in a hydrogen atom) calculated by Bohr was about 1/137th the speed of light. For those who're curious, that's ac, where a (alpha) is the fine structure constant, and c is the speed of light.

That would be more than 2,000 kilometers per second.

Of course, this is under classical mechanics. Under quantum mechanics, I'm not sure it's accurate to ascribe a certain "speed" to the electron, just a certain kinetic energy.

[Infernity]

[:o] So that's what he meant when he said "FAST!"

Which one is true?

-Infernity

[stormheller]

LOL!
Anyway, back to your question. The first electron shell can hold 2 electrons, the second can hold 8, the third can hold 8, the 4th can hold 18, etc. The shells keep gettin bigger and therefore able to hold more electrons as you move outward from the middle. Why do you think helium only has 2 valence electrons?

[Infernity]

Hmm what's after 18? your always say "etc" when you get to it... [sfty]

So, why and how are the electrons are gathering to a molecule only if it completes them to 8?

How can an 18 atom gather? Can there be an atom with 16 or so?

Will the 18 'give' 10 electrons to gather? Which means there can't be 16 or so, what-freaking-ever?

-Infernity

[kevin]

infern,

What you're interested in is the 'orbitals' that electrons are allowed to occupy around a nucleus. Incomplete orbitals seek to gain electrons to become so and are therefore reactive. That means sharing an electron with another incomplete orbital of another atom (bonding) or involving the complete transfer of the electron. The shape of an orbital and the number of electrons allowed to occupy it depend on quantum mechanical rules. (Don't ask me how.. )The shapes and numbers increase in complexity and size with proton number and energy state where energy state is approximated to the distance from the nucleus the electrons might be found.

http://www.orbitals.com/orb/index.html

A pretty decent overview can be found in here..

http://www.tcd.ie/Ch.../Tutorial 3.pdf

or elsewhere in plenty of general chemistry sections on the web.

[Infernity]

Thanks. Um I still ask................How? Well if not you, then another heh.

EDIT: Hmm you know what never mind, as soon as school starts, I'll ask my physics teacher.

-Infernity

[kraemahz]

Infernity,

No doubt your physics professor would give an evasive answer. That's my experience, at least.

I can give a quick, fairly easy to understand explaination for you. The electron orbitals are based on solutions to Schrodinger's equation, which is an equation that tells you probabilistically where an electron is most likely to be. They are not merely orbiting around in a circle as the Bohr model suggests, in fact they make some very strange orbital shapes.

The orbital levels are based off of the principle quantum number n, which can be any integer (1, 2, 3...), as the number goes up you need more and more room to accomidate all the extra electrons. The orbitals themselves are called s, p, d, f, and g. However, g doesn't show up at all on the periodic table, and f only in a small section so these are rarely dealt with.

The "s" orbital has only one fill state, it looks like a sphere and most closely resembles a planetary orbit like the Bohr model. Each fill state can hold two electrons (one that spins up, another that spins down).

The "p" orbital looks like a peanut, and it has three fill states. This means it can accomidate six electrons. For the first 3 levels of the periodic table, these are the only orbitals used this is the reason for the octet rule, but it only applies to groups 2 and 3 of the periodic table (those most used in organic chemistry). The s orbital can hold 2, the p orbital can hold 6, for a total of 8 electrons. Atoms want to be filled this way because when the whole orbital is full it is the least reactive it can be. That is, it has the lowest potential energy. If you think of it like a hill, a ball always wants to be at the bottom of the hill because at that point it has the least amount of energy, this same concept works here too.

The "d" orbital has four lobes and takes two shapes, one looks like a four-petal flower, the other like a peanut with a ring around its center. This orbital shows up in the transition metals in the center of the periodic table (like Palladium, which you asked about). It has five fill states and can hold ten electrons. Combined with the s and p orbitals, a d orbital atom can hold 18 electrons in its outer shell. The rare "f" orbital ones have an extra 7 fill states, or 14 electrons and can hold 32 in their outer shell.

[Infernity]

Wow, thanks kraemahz!!

No doubt the teacher wouldn't explain all that

-Infernity

[velocidex]

In heavy atoms, electrons move at relativistic speeds. If you work out what colour gold should be from the non-relativistic Schrodinger equation, it should be silver... but its not! If you use the relativistic Dirac equation, you correctly predict the colour of gold to be a yellowish colour.

[johnuk]

Yeah, I'm pretty sure electrons actually orbit closer to some fraction of the speed of light worth writing.

Orbitals are something you should learn about in more advanced chemistry. We didn't do anything on orbitals in physics. We used orbitals to explain the reaction of elements at a chemical level. Physics just stuck to shells. You should learn about orbital theory in chemistry when you're 17 - 19. The normal shells aren't enough to account for the bonding properties some elements exhibit, despite otherwise belonging to a logical trend.

The electrons orbit quickly enough that it can sometimes be preferable to refer to them as shells, sheets or layers of energy. Indeed, I suspect that is where the idea of a shells came from. Thinking of them as a single point in space spinning around an atom is perhaps a bit limiting. Indeed, I believe it's at these sorts of speeds that the question then arises, am I actually looking at a particle or a sheet of energy wrapped around the nucleus that exhibits the properties of a particle.

In our world, a wall is a solid object that we can't pass through due to our mass. But for an electron moving fast enough, if you put a wall in front of it the electron will seem to teleport through the wall and onto the otherside without actually travelling through the wall it's self. Spooky! Wooooo!

Also, as you increase the speed of an object, or it's velocity if you want to get picky, you give it more energy. Energy and mass are intertwined, so you also increase it's mass and that requires yet more energy to accelorate it by the same amount again, which is why it's theoretically impossible to reach the speed of light if you weigh anything to start off with.

All nice and complicated.

In short, yes. The electrons are moving very fast.

[JonesGuy]

Now, if I recall, the third electron layer actually has electrons that go near the speed of light for part of their journey. Once they go towards the nucleus, they accelerate until they act as if they are energy instead of a particle. Then, afterwards (once they pass through the nucleus as energy) they slow down to particles again.

Or at least, that was chemistry 15 years ago.

edit: the orbital diagram was a figure 8, if I recall.