[walman]

Hello.  I joined this forum after recently taking an interest in electrochemistry.  As I have been reading into the subject, as expected, I have almost as many unanswered questions as I have had answered.  So I would like to post some of my questions (a first of what will hopefully be many posts) in hopes that some of you may be able to answer one or more of them for me.  Please ignore any contradictions between questions as I have written these out in order of my research...


1) Is there an advantage in terms of energy output to an ionized atom?  For example, can a hydrogen atom have more energy potential if it is ionized?

2) If copper, for example, has many free electrons, how do the atoms maintain their electron count if they have electrons leaving their orbit?

3) In a conductor that permits the free motion of a large number of electrons, how are the free floating electrons prevented from leaving the conductor (ie: copper wire) in order for ionized atoms of the conductor to regain its original electron count once the electrical source is removed?

4) Do free electrons constitute the direction of the flow of an electric current in an electrical conductor?

5) I've read that "each electron moves a very short distance to the neighboring atom where it replaces one or more electrons by forcing them out of their orbits.  The replaced electrons repeat the process in other nearby atoms until the movement is transmitted throughout the entire length of the conductor."  Is this only the case in a conductor when an electric current is applied?  Or does this occur even when there is not an electric current applied to the conductor?  If the first, what sparks the first electron out of orbit of the rest are sparked by its jumping out of orbit (and if, assuming, the electric current affects the otter electron(s) in the first atom, does it continue to equally affect all of the other atoms the same (if that's the case, then does this mean that there are two sources of the activity?)?)?  If the latter is true, is this why metal is bendable and/or produces heat in the area where it is bent?

6) How does electricity break electrons loose from the influence of the nucleus?

7) Why do insulators (ie: glass, rubber, dry air, etc.) contain so few free electrons?

[Maz]

Hi Walman,  I am gonna take a stab at answering some of these questions for you, but don't take my word for it.  You're questions really aren't simple to answer, and involve a much deeper investigation then appears at first glance.  In fact, the heading "electrochemisty questions" really doesn't do them justice.  So I'll give this a shot, but there's a chance I might miss some stuff out.  I hope I don't get anything backwards, but I am really hungry and a bit sleepy.  I just couldn't pass up trying this though.

1.)  Well I am not really sure what you mean by "more energy potential".  When an atom is ionized, i.e. it looses or gains one or more electrons, the energies of the atom change.  One of the reasons for this is that the remaining electrons live in a different electric field then they did before the ionization occurred.  So from a quantum approach, they are now seeing a different potential then before (modeled by a perturbation), which results in a change in their wavefunctions and a change in their energy states. 

2/3.)  When people say that metals, in this case copper, have "free electrons", they are referring to a classic model of conduction...which isn't really correct.  First understand that in a strip of copper wire, there are many many copper (and some other contaminants) atoms.  These atoms are arranged in particular lattice structures (diamond, for instance is a particular lattice structure of carbon atoms).  Now the arrangement of atoms is incredibly important, as it will determine, among other things, how the electrons in a material behave. 

Copper has certain electrons in the wire that aren't well-confined.  I mean that the weakly bonded, outer shell (usually) electrons of copper aren't held very tightly by the nucleus of one atom and when a strong E-field is applied, the electron gains enough energy to travel to a neighboring nuclei where it may collide and transfer it's energy, or it's presence may be enough of a perturbation in the local e-field surrounding a second electron that that e- then goes off.  However, when I say strong E-field, understand that this is all relative.  The electron is so small and weakly charged that on a macroscopic scale, 1 V is a strong E-field.  Strong enough to see current flow.

Now electrons don't just go flying off copper that is just sitting there because it is energetically unfavorable.  I mean that the e- is "bound" to the nucleus of the atom through an electromagnetic interaction.  The energy of the atom system is lower with the e- in it's orbit then if it was gone.  If the e- leaves, then the atom is now charged and is generating a E-field attracting negative charged particles, and until is regains an e-, it will be at a higher energy state then before.  Since everything in nature is trying to achieve the lowest possible energy state, this scenario doesn't happen unless the orbiting e- gains enough energy that it's leaving will create a lower energy state then it's being there. 

4.)  Ah, an easy one.  The direction of flow of the electrons is technically opposite the direction of electric current.  Way way back in the day, current was defined as the flow of positive charge.  Now obviously protons don't go blitzing around a circuit.  However when an electron jumps off the atom and goes in say the +x direction, it leaves behind a "hole", or a locally positive area.  This hole, as the math works out, has nearly the same mass of an electron, and a positive charge.  Electric current is technically the flow of this positive charge, or the holes.  Remember, positive charge always moves in the direction of the electric field, and negative charges always move opposite the electric field. 

5.)  Well, of course what you said is not the ONLY case of what happens when an electric field is applied to a conductor.  Exactly what happens depends on the strength of the E-field, but it is by far the most common thing to happen.  However, if there is no E-field across a conductor, then there won't be any current flow, of course. 
As I tried to explain earlier, a conductor has many electrons that are weakly bound within it's structure.  However, they are still bound and unless some energy is added, they are UNLIKELY to spontaneously break free.  There is a probability of this happening, but it is low.  Also, this idea of the e- gaining enough energy to overcome an electromagnetic barrier is the reason for the 'sparking' you ask about.  Now the imposed E-field does affect all the electrons in an atom, but some are affected more strongly then others.  The outer electrons are the ones that are responsible for the flow, but the inner electrons are affected too.  However they are more tightly bound by the nucleus, or specifically the protons and the E-field generated by them.  Hence, they don't go flying off. 

6.)  I think I pretty much already covered this earlier.

7.)  Insulators don't necessarily contain few electrons, or fewer electrons then conductors anyways.  Insulators don't conduct well because their outer electrons don't break free as easily.  Now this isn't to say that individual atoms or molecules are harder to ionize then those atoms in conductors (although this can be the case).  This is dependent again on the structure of insulator with the atoms/molecules it is made out of. 

Maybe this terminology will help clarify what I mean:

Every material has two "bands".  These are the valence band and the conduction band.  Now in a given material there are electrons which reside in the valence band.  These electrons, when sufficient energy is supplied, can jump the "band gap" into the conduction band.  These bands are essentially collections of energy states derived from a quantum mechanical analysis of the wavefunctions of the electron given certain potentials.  The potentials are determined by the local environment of the e-, which is determined by the lattice structure, atomic structure, and/or molecular structure. 


Well, ok.  That was my try at answering these questions which, I think you can now see, are farther reaching then perhaps you originally thought.  General chemistry and even an electrochem. class will definitely clarify some of the things I wrote here in my terrible post, but if you really want to understand WHY these things are the way they are...take quantum mechanics and electrodynamics.  That will really answer your questions at a more fundamental level then your chemistry classes will. 

[walman]

Thank you for replying, Maz.  I appreciate it.  I want to say that all of your answers were helpful - if not to answer the question I asked, then certainly to clear up other issues that I did not bring up.  Here are my replies (feel free to respond to any or all if you wish).  I still have much to learn so forgive me if I confuse you with any of my statements...

1.)  Well I am not really sure what you mean by "more energy potential".  When an atom is ionized, i.e. it looses or gains one or more electrons, the energies of the atom change.  One of the reasons for this is that the remaining electrons live in a different electric field then they did before the ionization occurred.  So from a quantum approach, they are now seeing a different potential then before (modeled by a perturbation), which results in a change in their wavefunctions and a change in their energy states.

What I was trying to get at with this question (and seemed not to come to close to it ) was what role ionizing of atoms plays in reactions such as the combustion of gases such as hydrogen, and what role ionization plays in the energy output of such a reaction?  Also, is it the ignition of the molecule that ionizes the atoms, or can they be ionized prior to the ignition to perhaps result in a greater reaction?  If you understand what I'm asking but think I am asking about it in the wrong way, please try and shed whatever light you can on this.

2/3.)  When people say that metals, in this case copper, have "free electrons", they are referring to a classic model of conduction...which isn't really correct.  First understand that in a strip of copper wire, there are many many copper (and some other contaminants) atoms.  These atoms are arranged in particular lattice structures (diamond, for instance is a particular lattice structure of carbon atoms).  Now the arrangement of atoms is incredibly important, as it will determine, among other things, how the electrons in a material behave.

Copper has certain electrons in the wire that aren't well-confined.  I mean that the weakly bonded, outer shell (usually) electrons of copper aren't held very tightly by the nucleus of one atom and when a strong E-field is applied, the electron gains enough energy to travel to a neighboring nuclei where it may collide and transfer it's energy, or it's presence may be enough of a perturbation in the local e-field surrounding a second electron that that e- then goes off.  However, when I say strong E-field, understand that this is all relative.  The electron is so small and weakly charged that on a macroscopic scale, 1 V is a strong E-field.  Strong enough to see current flow.

Now electrons don't just go flying off copper that is just sitting there because it is energetically unfavorable.  I mean that the e- is "bound" to the nucleus of the atom through an electromagnetic interaction.  The energy of the atom system is lower with the e- in it's orbit then if it was gone.  If the e- leaves, then the atom is now charged and is generating a E-field attracting negative charged particles, and until is regains an e-, it will be at a higher energy state then before.  Since everything in nature is trying to achieve the lowest possible energy state, this scenario doesn't happen unless the orbiting e- gains enough energy that it's leaving will create a lower energy state then it's being there.

Some of this is beyond what I currently understand (mainly in quantum mechanics and electromagnetism).  I wonder if you could recommend some books on what you've discussed here (and on electrochemistry and closely related subjects, for that matter)?

I will ask what comes to mind, though:

First, is it possible for an atom to lose all of its electrons?  If so, what is it then considered, and what are its potential implications?

Second, can you elaborate on the idea of all things in nature trying to achieve the lowest possible energy state?  I haven't heard of that idea.

Third, is there a pattern(s) to the transfer of electrons when an electrical current, for example, is applied to a molecule?  Do they have preferances on where they move, how they move, etc. (I know you mentioned lattice structures, but I wonder if there's anymore to that?)?

4.)  Ah, an easy one.  The direction of flow of the electrons is technically opposite the direction of electric current.  Way way back in the day, current was defined as the flow of positive charge.  Now obviously protons don't go blitzing around a circuit.  However when an electron jumps off the atom and goes in say the +x direction, it leaves behind a "hole", or a locally positive area.  This hole, as the math works out, has nearly the same mass of an electron, and a positive charge.  Electric current is technically the flow of this positive charge, or the holes.  Remember, positive charge always moves in the direction of the electric field, and negative charges always move opposite the electric field.

What exactly is this hole?  Is it kind of like a super-miniature black hole?  How does it have mass?  And if it's a positive charge, doesn't that mean it's like adding a proton in terms of the atom's charge?

Also, while unrelated, what is a nucleus made up of and what can't protons and neutrons escape an atoms (or can they?)?

5.)  Well, of course what you said is not the ONLY case of what happens when an electric field is applied to a conductor.  Exactly what happens depends on the strength of the E-field, but it is by far the most common thing to happen.  However, if there is no E-field across a conductor, then there won't be any current flow, of course.

As I tried to explain earlier, a conductor has many electrons that are weakly bound within it's structure.  However, they are still bound and unless some energy is added, they are UNLIKELY to spontaneously break free.  There is a probability of this happening, but it is low.  Also, this idea of the e- gaining enough energy to overcome an electromagnetic barrier is the reason for the 'sparking' you ask about.  Now the imposed E-field does affect all the electrons in an atom, but some are affected more strongly then others.  The outer electrons are the ones that are responsible for the flow, but the inner electrons are affected too.  However they are more tightly bound by the nucleus, or specifically the protons and the E-field generated by them.  Hence, they don't go flying off.

You say it's unlikely that they will spontaneously break free.  In the cases where it does happen, though, is it unknown what causes it, or do we know?  If so, what does cause it?  Or what are the theories?

7.)  Insulators don't necessarily contain few electrons, or fewer electrons then conductors anyways.  Insulators don't conduct well because their outer electrons don't break free as easily.  Now this isn't to say that individual atoms or molecules are harder to ionize then those atoms in conductors (although this can be the case).  This is dependent again on the structure of insulator with the atoms/molecules it is made out of. 

Maybe this terminology will help clarify what I mean:

Every material has two "bands".  These are the valence band and the conduction band.  Now in a given material there are electrons which reside in the valence band.  These electrons, when sufficient energy is supplied, can jump the "band gap" into the conduction band.  These bands are essentially collections of energy states derived from a quantum mechanical analysis of the wavefunctions of the electron given certain potentials.  The potentials are determined by the local environment of the e-, which is determined by the lattice structure, atomic structure, and/or molecular structure.

So it's the lattice structure, atomic structure, and/or molecular structure that determines the strength of the hold of the outer electrons of an atom?



Again, thank you very much for your input.  You've definately helped me to answer many of the questions I had, and prompted me to ask more !  Thanks again.

[Maz]

As far as recommended books/classes, you are probably much better off taking a physical chemistry class as opposed to dicking around with quantum mech.  They are essentially the same thing except quantum mech. will go into much deeper detail concerning the theory and math.  Physical chemistry will get you up to speed for an operational understanding about the major applications of quantum mech...especially in chemistry.  It's also easier and more fun, IMO.

As far as electricity and magnetism go, you'll probably be fine just taking a second semester college lower-division physics class.  That will again get you through most of the basic theory and set you up for the major applications.  It's also loads of fun (neat stuff). 

A good P-Chem book coupling is : Intro to Quantum Mechanics in Chemistry by Ratner with Molecular Quantum Mechanics by Atkins. 

A great Electrodynamics book is Introduction to Electrodynamics by Griffiths, but it may be a little advanced and he uses his own symbols that no-one else uses so it can get confusing. 

So as to some of your questions (not gonna try and answer all of em right now):
1.)  It is possible for an atom to be stripped of all its electrons.  We do it routinely to Hydrogen, at which point it is nothing more then a proton with no more profound implications than just that.  For heavier elements, it naturally takes A LOT more energy and we don't do it all that often.  There isn't anything all that special about, I think. 

2.)  So for a deep understanding of this idea, you would want to take a statistical mechanics class.  However I know you don't...hell I really don't want to drudge through the math, so I am gonna try and answer it using a qualitative argument.  However, I just have to say that this is a really fundamental concept and is one of those rules that "governs all the universe".  When doing problems, both chemistry and physics, following the energy saved my skin many a time. 

You see examples of the fact that things try to achieve the lowest possible energy state everyday. 

Why do compasses point north and south?  The alignment of a dipole in a magnetic field is the result of the force the earth's mag. field is putting on the north and south poles of the dipole.  When the dipole repositions itself so that it's south pole is pointing towards the earth's north pole and it's north pole towards the earth's south pole, the force from the earth's mag. field on it is minimized.  Two steps further, the potential energy is minimized. 

The same reasoning can be applied to commonly noticeable things like: "what goes up must come down", diffusion, and of course electricity.  Ohhh...what a smooth segway into question 3...

3.)  There is a pattern to the transfer of electrons when a voltage is applied, of course.  Heh, in general the movement of the electrons is taught as "the direction of decreasing energy".  In other words, electrons will move towards areas of relative positive charge when an E-field is applied.  However, I think you are mixing up two distinct ideas.  Voltage, or in other words an E-field created from a separation of charge, is different from current.  They are related, of course, via Kirchoff's laws, but I am mostly going to talk about E-field applied on a system because that is the really fundamental thing here. 

So, in general direction of movement of electrons in an E-field is opposite the E-field's direction, or towards relatively positive charge.  In a material, the specific direction is determined by the lattice structure and/or molecular structure.  Macroscopically, you only see current flowing through the wire throughout the circuit.  Atomically, the electrons are bouncing from potential well to potential well across the material. 

4.)  No no, a 'hole' in the context we were talking about is NOT some crazy super-miniature black hole.  Imagine you have a material with a certain structure at equilibrium.  Now all of a sudden, a single electron magically ups and leaves the structure so that the material is at -1 electron.  The gap left by that electron is what we call a "hole" in e&m.  It has the same mass as an electron, but a positive charge.  I don't wanna go too much into detail on this and why it "has a mass" partially because it's complicated math, and partially because I am not sure I believe it.  At the very least, it is a good approximation.  Remember, it is NOT a proton. 

Alright, this is the last one I am gonna play with today.  Then i'm gonna polish off my ho-ho's with a glass of milk. 

5.)  According to the Standard Model, a nucleus is made up of a variety of subatomic particles.  Usually these are the protons and neutrons we are familiar with.  You could go smaller then that and start talking about how quarks make up protons and neutrons, but let's stick with the basics here. 

Protons and neutrons that are really, really, really closely packed together comprise the nucleus.  Now you know the protons should repel each other, so why do they get so close together?  The answer is that the nuclear force, a.k.a. the strong force, dominates at that range.  Suffice it to say that the nuclear force is much stronger then the electroweak force, (electricity, magnetism, and the 'weak' force are all actually the same thing...don't ask why right now). 

Now depending on the makeup of the nucleus, it can be stable or unstable.  Certain nuclei, ¹H, ¹²C, ³⁹K, are stable.  Others, ¹⁴C, ⁴¹K, aren't stable.  These nuclei do breakdown, and spit out protons and neutrons in what is known as radioactive decay.  A nucleus can decay in a variety of ways and the process and products of the decay are...complicated.  If you want to learn that, you can go into nuclear chemistry (way cool and not too hard, especially if Mitch is your T.A.) or nuclear physics.  They are practically the same thing, and the difference is like the difference between P-chem and Quantum Mech. 

Hope this all helped. 

[xiankai]

What I was trying to get at with this question (and seemed not to come to close to it Wink) was what role ionizing of atoms plays in reactions such as the combustion of gases such as hydrogen, and what role ionization plays in the energy output of such a reaction?  Also, is it the ignition of the molecule that ionizes the atoms, or can they be ionized prior to the ignition to perhaps result in a greater reaction?  If you understand what I'm asking but think I am asking about it in the wrong way, please try and shed whatever light you can on this.

in reactions, the bond between atoms are broken and then the atoms form new bonds between new atoms, thus forming new compounds. the ionization of these atoms is a depends on how the bond is dissociated - heterolytic cleaving means the shared electrons in the bond are transferred to one atom (NaCl --> Na⁺ + Cl^-), homolytic cleaving when the electrons are split equally (O₂ --> 2O). heterolytic cleaving is more common as one atom tends to be more electronegative (electron-attracting) than the other.

if by ignition you mean supplying the activation energy to break the bonds first, yes it ionizes the atoms. if you ionize the atoms prior to the reaction, the ions will react readily since they are energetically unstable. the rate of reaction is faster, but (correct me if im wrong, but i interpret 'greater reaction' as to mean greater yield) the amount reacted remains the same, because it eventually comes to equilibrium.

First, is it possible for an atom to lose all of its electrons?  If so, what is it then considered, and what are its potential implications?

such an entity would only last for a very small amount of time before it regains back its electrons - just as in the self-ionization of water, H⁺ almost does not exist, rather it is present as H₃O⁺, or a protonated water molecule. the hydrogen ion itself however, would possibly be the strongest acid by its definition of pH.

Second, can you elaborate on the idea of all things in nature trying to achieve the lowest possible energy state?  I haven't heard of that idea.

However, I just have to say that this is a really fundamental concept and is one of those rules that "governs all the universe".

energy can be quite hard a concept to grasp - you can't see it, you can't feel it, but you know its out there.  and one of its certain quirks is that it likes to flow from high energy to low energy, to balance out the energy difference.

What exactly is this hole?  Is it kind of like a super-miniature black hole?  How does it have mass?  And if it's a positive charge, doesn't that mean it's like adding a proton in terms of the atom's charge?

you may like to look up the Dirac sea and the hole theory. you can ignore the quantum buzzwords, and still manage to get the gist of the idea 

Also, while unrelated, what is a nucleus made up of and what can't protons and neutrons escape an atoms (or can they?)?

they can escape the atom if you provide a strong enough energy boost - this is how radiation and radioactive decay occurs.

You say it's unlikely that they will spontaneously break free.  In the cases where it does happen, though, is it unknown what causes it, or do we know?  If so, what does cause it?  Or what are the theories?

this is due to the wave-like nature of the electron. and as a wave, it has a chance to be in different positions at any given time. this is a fundamental concept of quantum physics - that matter can act as a particle or a wave. some people believe that it is due to hidden influences (hidden variable theory), some accept that's the way it seems.

So it's the lattice structure, atomic structure, and/or molecular structure that determines the strength of the hold of the outer electrons of an atom?

including external forces such as heat, interaction with other atoms and such, yes.

[Brown]

Every material has two "bands".  These are the valence band and the conduction band.  Now in a given material there are electrons which reside in the valence band.  These electrons, when sufficient energy is supplied, can jump the "band gap" into the conduction band.  These bands are essentially collections of energy states derived from a quantum mechanical analysis of the wavefunctions of the electron given certain potentials.  The potentials are determined by the local environment of the e-, which is determined by the lattice structure, atomic structure, and/or molecular structure. 

Can you explain clearly about the valence band and the conductive band by using MO theory ( Molecular Orbital theory)? How do two bands form?. Thanks