Do Atoms Need Fuel? A Curious Question

[36grit]

Do atoms require fuel or does the electron move about the nucleous in the some way the Earth rotates the sun?

Maybe it's a stupid question but I've always wondered about this.

 

[dacruick]

Interesting. I don't know the answer to this but I'm going to go ahead and assume its a variety of sources of kinetic energy. Whether it be light, heat, gravity, friction. I would like to hear an answer from someone who actually knows what they are talking about.

 

[K^2]

Do atoms require fuel or does the electron move about the nucleous in the some way the Earth rotates the sun?

Maybe it's a stupid question but I've always wondered about this.

It's a little complicated. Well, first of all, no, it's not fueled by anything, but it's not like planetary motion either.

Planets do slowly lose their kinetic energy and spiral down towards the Sun. Very, very, very slowly. Electrons in the atom can't do that. There are only certain specific levels they can occupy, and if the levels bellow are already occupied, the electron cannot lose energy and descend.

All of this is made more complicated by the fact that electrons aren't localized. They are not in one specific point at anyone specific time, but rather distributed around the atom. Because of that, some electrons aren't even rotating around the atom at all. They have zero angular velocity, and yet they cannot fall down onto the atom.

Unfortunately, to really understand all of this, you need to know a bit of quantum mechanics.

 

[mathman]

The answer comes from quantum theory. Electrons in atoms come in states. There is a minimum state - if all the atoms in something are at a minimum, it would be at absolute zero. As things get warmer, the electrons go to higher states by absorbing photons.

 

[K^2]

Only the top few electrons of rather heavy atoms may be thermally excited at normal temperatures. To excite an electron in hydrogen atom, for example, you need 10eV, which is equivalent to temperature of 110,000K or nearly 200,000°F.

 

[Danger]

To excite an electron in hydrogen atom, for example, you need 10eV, which is equivalent to temperature of 110,000K or nearly 200,000°F.

You don't encounter that in Alberta on a daily basis, so I guess that we're a bit hydrogen-deprived in that regard.

 

[Drakkith]

The positive electric force of the protons in the nucleus are attracting the negative charge on the electrons. However, electrons can only get close to the nucleus in steps. When an electron is excited, say by light striking it, it can "jump" up a few steps by absorbing the energy of the light. The reverse is also true. It can "jump" back down and LOSE energy to get closer to the nucleus by emitting a photon with the same energy as it loses to jump down a step. Unless excited, electrons will stay at the lowest energy level possible.


Between these steps there are no half steps or anything else like that. The electrons CANNOT jump to a spot that is halfway between 2 steps. That is what the word Quantum means: the minimum amount of any physical entity involved in an interaction. An example is a photon, which can only be absorbed or emitted wholly. IE, an electron can absorb a whole photon, or it won't absorb it at all, there is no middle ground.


Note that the electron cannot "enter" the nucleus, or join it, or anything like that.

 

[Danger]

Note that the electron cannot "enter" the nucleus, or join it, or anything like that.

I respectfully disagree with that last statement, but only under extreme circumstances. In the case of a neutron star, electron degeneracy pressure is no longer strong enough to overpower gravity. The electrons are essentially squished into the protons in order to create more neutrons. (Charge cancellation.) Hence the existence of the densest substance attainable—neutronium.

 

[36grit]

Between these steps there are no half steps or anything else like that. The electrons CANNOT jump to a spot that is halfway between 2 steps. That is what the word Quantum means: the minimum amount of any physical entity involved in an interaction. An example is a photon, which can only be absorbed or emitted wholly. IE, an electron can absorb a whole photon, or it won't absorb it at all, there is no middle ground.

How many steps are there? Do the electrons of heavy materials have more steps than those of lighter materials?
do these photons somehow "wind up" the atom and keep it spinning and working?

 

[Drakkith]

I respectfully disagree with that last statement, but only under extreme circumstances. In the case of a neutron star, electron degeneracy pressure is no longer strong enough to overpower gravity. The electrons are essentially squished into the protons in order to create more neutrons. (Charge cancellation.) Hence the existence of the densest substance attainable—neutronium.

Touche Danger, but like you said, only under extreme circumstances. =)

 

[Drakkith]

How many steps are there? Do the electrons of heavy materials have more steps than those of lighter materials?
do these photons somehow "wind up" the atom and keep it spinning and working?

I don't believe that there are a set number of steps. Heavier atoms have more protons, which means they can attract and stably hold more electrons, so they will have at least as many steps as they have electrons. Once excited, i don't know if there is a set step that the electron will simply have too much energy to be contained in the atom.

The photons are absorbed and transfer their energy to the atoms, either exciting electrons, or providing energy in the form of heat. An atom doesn't REQUIRE photons, and will not simply fall apart if it doesn't receive any energy. The attractive forces between the protons and electrons keep the electrons orbiting around the nucleus, and the strong nuclear force keeps the protons and neutrons together in the nucleus and keeps the protons from simply repelling each other out of the nucleus.

Any material with a temperature above 0 kelvin will radiate energy out in the form of photons, with a higher temperature giving higher energy and frequency. Look up Black Body Radiation. So the atoms naturally want to get rid of extra energy and stay in the lowest state possible.

This is how I understand it at least. It may not be 100% correct, but i believe its a good start at understanding it.

 

[jtbell]

Note that the electron cannot "enter" the nucleus, or join it, or anything like that.

In fact this does happen, with observable results. The quantum-mechanical wave function of an atomic electron is in general not necessarily zero at the location of the nucleus. This leads to a finite probability (with certain isotopes) for the process known as electron capture, in which a proton and an electron combine to produce a neutron and a neutrino. This is related to beta-decay, in which a neutron converts to a proton, electron and antineutrino.

 

[brainstorm]

What if there is a thermodynamic system in equilibrium, say a hydrogen cloud in space. If it has a certain temperature, the particles are bouncing around at a particular speed, correct? However, it would also be in tension according to the conflict between its expansionary tendency, as a function of its kinetic energy, and its gravitational attraction. So if it were condensing, then its energy-density (temperature) would be increasing and causing electrons to get excited and emit radiation, right? And if it were expanding, its energy-density would be decreasing, which would cause the molecules to maintain constant electron-states and emit less radiation.

So if it were expanding, would the atomic electrons remain in the same orbits indefinitely until acted upon by an outside force, either particle-collision or radiation-absorption? Or would entropy cause them to eventually release further radiation and continue to drop to lower orbits/levels? In other words, do atoms have an "absolute zero" configuration that keeps them intact with their mass as energy without being capable of further "cooling" into further disorganized (less energetic) states/configurations?

Is this question too convoluted?

 

[Danger]

It appears that I stand corrected, since JT brought up something that I was unaware of. I seem to recall seeing something about spontaneous electron capture in a SciAm about 40 years ago, but had totally forgotten about it.

 

[Drakkith]

In fact this does happen, with observable results. The quantum-mechanical wave function of an atomic electron is in general not necessarily zero at the location of the nucleus. This leads to a finite probability (with certain isotopes) for the process known as electron capture, in which a proton and an electron combine to produce a neutron and a neutrino. This is related to beta-decay, in which a neutron converts to a proton, electron and antineutrino.

Of course. But in general, most everyday matter does not experience this. Or at least the matter that the average person encounters on a daily basis. Didn't want to overcomplicated things. =)

 

[K^2]

In the case of a neutron star, electron degeneracy pressure is no longer strong enough to overpower gravity. The electrons are essentially squished into the protons in order to create more neutrons.

I doubt that this is the main process. For the most part, I'd expect standard beta+ decay. In beta+, a proton can go to a lower state by becoming a neutron and loosing positive charge by emitting a positron. A free neutron has slightly higher energy than a free proton + free electron, so a free neutron decays to proton+positron. But in a neutron star, Coulomb repulsion opposing gravity reverses this equilibrium, and protons begin decaying into neutrons. The positrons then annihilate as they encounter free electrons.

The electron capture probably happens as well, but since it's going to have both the weak interaction and electron-proton coincidence probability, vs just weak interaction in the beta+ decay, it's not going to be the dominant process.

In fact this does happen, with observable results. The quantum-mechanical wave function of an atomic electron is in general not necessarily zero at the location of the nucleus. This leads to a finite probability (with certain isotopes) for the process known as electron capture, in which a proton and an electron combine to produce a neutron and a neutrino.

Any idea how they detect this? I would imagine that any atom in which this can happen can also beta+ decay, so you'd have to look for difference between neutron production and annihilation events, and with neutrinos being so difficult to detect, how would you know if there are a few extras being produced?

Of course. But in general, most everyday matter does not experience this. Or at least the matter that the average person encounters on a daily basis. Didn't want to overcomplicated things. =)

Well, electron wave-function extending into nucleus is quite common. It's just the capture process that isn't.

 

[Phyisab****]

Well the discussion has strayed quite a bit from the original question, and I'm not sure anyone answered in a straightforward manner.

OP, it does not take energy to maintain an isolated atom in a certain state. The analogy with planetary motion is poor, but I suppose it is good enough.

 

[Drakkith]

Well the discussion has strayed quite a bit from the original question, and I'm not sure anyone answered in a straightforward manner.

OP, it does not take energy to maintain an isolated atom in a certain state. The analogy with planetary motion is poor, but I suppose it is good enough.

Perhaps, but i think that many of these posts were required for the OP to really understand WHY it didn't need fuel.