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The flow of current in a (semi-)conductor is often described as holes and/or electrons moving between atoms. In this context:

  • Is an atom with a hole the same thing as a positive ion (cation), and
  • Is an atom with an electron the same thing as a negative ion (anion)?

I already understand what cations and anions are. And I am not asking about current flow. I just want to know if the two questions in the above list are true or false.

However you answer, kindly explain your reasoning (why is it yes, or why is it no)?

I have already searched related questions here, but none of them seem to answer this.

EDIT: I screwed up when I asked this! I just added the text in italics "an atom with" above, which is what I had in mind from the start. Sorry.

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    \$\begingroup\$ No. They may behave similar though \$\endgroup\$ – PlasmaHH Feb 2 '18 at 18:49
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    \$\begingroup\$ A hole is the absence of an electron in a orbit where they are usually found in an atom. \$\endgroup\$ – Sunnyskyguy EE75 Feb 2 '18 at 18:59
  • \$\begingroup\$ @TonyStewart.EEsince'75 Thanks, but isn't that the very definition of a cation? \$\endgroup\$ – Mike Waters Feb 2 '18 at 19:02
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    \$\begingroup\$ A Cation just means fewer electrons than protons or more protons than electrons i.e. +ve ion \$\endgroup\$ – Sunnyskyguy EE75 Feb 2 '18 at 19:09
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    \$\begingroup\$ they are both true when referring to p-semiconductor and n-semiconductor in zero current state (you did not ask about that though) \$\endgroup\$ – jsotola Feb 3 '18 at 18:50
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Neither are true.

A hole has a one unit positive charge. Its position is essentially that of the atom which is short of one electron. When it moves, the atoms do not move, but electrons move to move the vacancy around. The effective mass of the hole is a complicated function of the material.

A positive ion is an atom that has lost one electron. It also has one unit positive charge, and a mass more or less that of the uncharged atom. When it moves, it moves.

An electron is an electron, with a one unit negative charge.

A negative ion is an atom that has gained one electron, so has a one unit negative charge.

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  • \$\begingroup\$ Thanks, but motion "current flow" is not part of my question. (See my comment on Kevin's answer). Maybe I didn't make that clear enough. \$\endgroup\$ – Mike Waters Feb 2 '18 at 19:33
  • \$\begingroup\$ Thanks, but current flow is no part of my answer, only masses, charges and movement. \$\endgroup\$ – Neil_UK Feb 2 '18 at 19:51
  • \$\begingroup\$ @MikeWaters Both are false. And since to make something false you only must find some differences (any one or more reasons counts as some), there is no reason to list all possible reasons. It's sufficient to find any one reason and call it good. Since physics involves many models at various levels, there is quite a spectrum of possible "no, they are both false because ..." answers available. You need to be more precise if you want better, I think. \$\endgroup\$ – jonk Feb 2 '18 at 22:26
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    \$\begingroup\$ @MikeWaters : in a solid material, holes are charge carriers, i.e. motile objects. Localizing a hole to a particular atom is pointless (the hole moves through a crystal lattice of near-fixed atoms). There are no distinct 'ion' individual atoms, the outer electrons are fully hybridized over the lattice. \$\endgroup\$ – Whit3rd Feb 2 '18 at 22:37
  • \$\begingroup\$ @Whit3rd Correct!! This is solid state physics here: the Fermi surface derived from the lattice structure and occupation of energy bands. \$\endgroup\$ – jonk Feb 2 '18 at 22:55
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Is an atom with a hole the same thing as a positive ion (cation), and

Yes, both are ways of referring to an atom with a net positive charge, but a conductor or semiconductor has many holes but are not usually thought of as having ions, since the holes (or excess electrons) are moving all the time and therefore no atom continues to be an ion for long, so if we are talking about holes e.g. in semiconductor physics, I would be surprised to hear discussion of ions.

(Contrast ionic compounds, which have distinct cations and anions, and are most commonly, but not always, non-conductive.)

Is an atom with an electron the same thing as a negative ion (anion)?

Well, most atoms always have some electrons; I assume you meant "with an excess electron", in which case my answer is the same as above — yes, that is the same thing but it depends on context which you should use.

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  • \$\begingroup\$ "Electrons may move between atoms, changing which one is the ion." I fully agree with this! \$\endgroup\$ – Mike Waters Feb 2 '18 at 19:20
  • \$\begingroup\$ But that involves current flow. But I am speaking of an instantaneous snapshot where nothing is moving (yet). \$\endgroup\$ – Mike Waters Feb 2 '18 at 19:23
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    \$\begingroup\$ @MikeWaters The point of the concept of a hole is to be able to talk about something persistent that evolves over time in a different way than some atom-with-a-net-positive-charge. If time did not exist, then the concept of a hole would not be as useful. (I've updated my answer with some more words on the subject.) \$\endgroup\$ – Kevin Reid Feb 2 '18 at 19:38
  • \$\begingroup\$ Thanks, Kevin. Before you edited your answer in response to my clarified question, you said something about solids vs. gases. That was interesting. I am comfortable with air ionization technology (oxygen and CO2, actually; the nitrogen cannot be ionized by our method), and we happen to be in the business of manufacturing room ionizers for air purification. I was trying to understand better how ionization of gases might be compared to electron flow in a solid. \$\endgroup\$ – Mike Waters Feb 8 '18 at 21:46
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    \$\begingroup\$ @MikeWaters Sorry, it would exceed my knowledge to say anything confidently there. The snippets I have include "it's all charge carriers, but ions are much heavier than electrons" and "in metals, electrons aren't really associated with individual atoms", but from my perspective you'd be better off trying for an answer from the folks over at physics.stackexchange.com — if you can nail down the question more precisely. \$\endgroup\$ – Kevin Reid Feb 8 '18 at 21:50
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Yes, each valence lattice vacancy (hole) is always a cation, since holes are always part of postive-charged atoms. Electrons are different, since they can be part of a neutral, un-ionized atom.

In p-type semiconductor, because of thermal vibration, each neutral acceptor dopant atom (say boron) will grab an electron from a neutral silicon neighbor. This creates a pair of opposite charges: a negative boron ion and a positive silicon ion. The boron now has excess negative charge (more electrons than protons,) while the silicon has excess positive charge (more protons than electrons.) But then the magic happens: that positive silicon ion can grab an electron from a silicon neighbor, ionizing the neighbor while becoming neutral itself. At the same time the negative boron ion remains trapped. Thermal vibrations knock the mobile charges around, so the opposite charges soon are widely separated. The material becomes a grid of unmoving negative borons, plus an equal cloud of mobile positive-ionized silicons.

In other words, inside p-type semiconductors, only the "ionization" is moving around, while each positive-charged atom remains locked into the crystal lattice.

Also, take careful note that in physics, "lack of electrons" isn't a thing. (Vacuums lack electrons. Is vacuum therefore made of positive ions? No, that's silly.)

When we say "lack of electrons," we really mean "initially neutral atom, then an electron is removed, leaving an exposed, un-cancelled proton; a positive ion." Holes are actually the un-cancelled protons of the silicon crystal lattice. They really are positive-charged particles. (Only protons can supply positive charge. Missing electrons cannot. "Lack of electrons" just means "un-cancelled protons.") The holes move; the positive ionization moves, but the protons themselves stay still. Like any conductor, the p-type material is overall neutral, (negative borons and positive silicons,) even though it's filled with mobile charges.

Are electrons actually negative ions? Nope.

In the same way that protons aren't positive ions, electrons aren't negative ions. (See, the electrons aren't actually the opposite of holes. Saying they're opposites is just a simplified convenient concept, but not fundamentally true. Electrons are opposites of protons. And negative ionization is the opposite of positive ionization. "Holes" are mobile positive ionizations.)

On the other hand, conduction electrons in n-type semiconductor do create negative ions. Notice that the entire crystal is made of protons and electrons, even though the vast majority of atoms are not ions. All those electrons are part of the valance level; the unmoving bonds between atoms in the crystal. Valence electrons aren't negative ions.

In n-type silicon, each neutral dopant atom, say phosphorous, loses one electron to a neutral silicon neighbor. A pair of opposite charges is created: the boron becomes a positive ion (one un-cancelled proton,) while the silicon neighbor is a negative ion (one extra electron.) Then, the negative phosphorus remains trapped in the lattice, while the "ionization" of the silicon neighbor moves around. This isn't quite the opposite of p-type silicon, because in the p-type crystal, the positive ions were created by exposing the hidden positives inside a previously-neutral atom, rather than by adding positives.

In n-type, both the negative ionization and the electrons are hopping together from atom to atom. Yet at the same time, the entire lattice is made of electrons (neutralized electrons, each one bound close to a proton in the silicon atoms.) The n-type crystal is a group of trapped positive phosphorus ions, immersed in an equal cloud of negative silicon ions created by mobile conduction electrons. Like any conductor, the material is overall neutral, even though it's filled with mobile charges.

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1.) Is a hole the same thing as positive ion (cation)?

Ans.) No, an ion is an atom or molecule with some charge either positive(cation) or negative (anion). Atoms consist of electrons, neutrons and protons which are called sub atomic particles. Now if your question is, is hole same as proton, the answer is still no, holes are merely absence of electron, an atom always tries to attain neutrality that is number of protons and electrons would be same, if it has less number of electrons it would try to get more electrons, this is explained as hole which is ability to accept an electron.

2.) Is electron same as anion?

Ans.) No, refer to above answer regarding difference between sub atomic particles and ions.

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  • \$\begingroup\$ I am not asking "is hole same as proton". Protons remain in the nucleus. They do not orbit an atom. \$\endgroup\$ – Mike Waters Feb 2 '18 at 19:10

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