h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

It is possible to determine the charge on a single-element ion from the periodic table. ('Single-element' meaning 'an ion containing only one element', such as (Li+)--some ions are combinations of more than one element, such as (OH-), the hydroxide ion.)

Generally, metals form cations (positive ions) and nonmetals form anions (negative ions), in an attempt to "match up" with the noble gases. (All elements want to be noble... ) On a periodic table (there is one at http://www.webelements.com/, which you may want to open in a different window as a reference), the metals are on the left and the nonmetals are on the right. The noble gases are the rightmost. For a metal on the far left edge (such as sodium, Na) to "match up" with a noble gas, it must lose one of its electrons. Losing an electron gives its ion a positive +1 charge.


Example (metal):

Sodium (Na) has 11 electrons, because its atomic number of '11' means that it has 11 protons, and therefore 11 electrons as well. Sodium "wants to" have the same number of electrons as the closest noble gas, which would be neon (Ne). Neon has an atomic number of 10, which means it has 10 protons and 10 electrons. For sodium to go from 11 electrons (Na) to 10 elections (Ne), it "gets rid of" one electron. If sodium loses one electron, its charge becomes (+1), because now it has 11 protons and only 10 electrons. Therefore the charge on a sodium ion is (+1). Metals almost always *lose* electrons when they form ions, so metals almost always form positive ions (cations).


Example (nonmetal):

Now let's take the example of oxygen (O, atomic number 8), a nonmetal. Oxygen has 8 protons and 8 electrons in its neutral form. The closest noble gas to oxygen is neon (Ne, atomic number 10). For oxygen to go from 8 electrons (its neutral state) to 10 electrons (the state it wants to be in), it needs to gain 2 electrons. Should it succeed in gaining these 2 electrons, its charge will become (-2), because it has 8 protons and 10 electrons. Nonmetals will almost always *gain* electrons when they form ions, so nonmetals almost always form negative ions (anions).


Visually, those elements on the right side of the periodic table (nonmetals) have to move to the right (by gaining electrons) to become noble gases. Gaining electrons turns them into *negative ions*.

Those elements on the left side of the periodic table (metals) have to move to the left (and then around to the other end), by *losing electrons* and becoming *positive ions*.

The *number* of electrons that an element will gain or lose is dependant on its /distance/ to the noble gases. The *charge* is dependant on whether it /gains or loses/ the electrons to get there.

Note: this will only work if the element in question is one of the "representative elements"--representative elements are those in the first two columns furthest to the left, and also those in the six columns furthest to the right. Taking out the transition elements (those in the inner-rectangle) leaves the representative elements.


Shee

Note: There's periodic table in h2g2. Just do a quick search.

Eh... I figured that there would be one, somewhere here... And if not, doubtless that somewhere else on a BBC page they would have one... But I was lazy... (That's my excuse anyway... Go for the one already in the Bookmarks... *grin*)

Guess who's the author??

Now, the Shee, ket me comment on some things you wrote that are over-simplifications, and should not stand here uncommented:

"It is possible to determine the charge on a single-element ion from the periodic table. ('Single-element' meaning 'an ion containing only one element', such as (Li+)--some ions are combinations of more than one element, such as (OH-), the hydroxide ion.)"

Single elements are NOT charged a prori. Even so, single elements can have different charges e.g. Mg)+1) it must NOT be mg(2+) necessarily.

"Generally, metals form cations (positive ions) and nonmetals form anions (negative ions), in an attempt to "match up" with the noble gases. (All elements want to be noble... )"

BEWARE: Over-simplification(!!!) no element *wants* to become anything. Metal elements do not give their electrons away for free: it will *always* cost energy to move one electron away and put it somewhere else. The noble-gas rule works nicely for some examples, that is why it's taught like that in school. But it's not accurate as soon as you leave the second period.

"On a periodic table (there is one at webelements, which you may want to open in a different window as a reference), the metals are on the left and the nonmetals are on the right. The noble gases are the rightmost. For a metal on the far left edge (such as sodium, Na) to "match up" with a noble gas, it must lose one of its electrons. Losing an electron gives its ion a positive +1 charge."

Thank you but somehow it saddened me that MY periodic table entry (and related entries did not get to you)

" Example (metal): Sodium (Na) has 11 electrons, because its atomic number of '11' means that it has 11 protons, and therefore 11 electrons as well. Sodium "wants to" have the same number of electrons as the closest noble gas, which would be neon (Ne). Neon has an atomic number of 10, which means it has 10 protons and 10 electrons. For sodium to go from 11 electrons (Na) to 10 elections (Ne), it "gets rid of" one electron. If sodium loses one electron, its charge becomes (+1), because now it has 11 protons and only 10 electrons. Therefore the charge on a sodium ion is (+1). Metals almost always *lose* electrons when they form ions, so metals almost always form positive ions (cations)."

Thanks for the lesson, Shee, but: a - See above and b - Metals do also form anions (Na(-1) for example)

"Example (nonmetal): Now let's take the example of oxygen (O, atomic number 8), a nonmetal. Oxygen has 8 protons and 8 electrons in its neutral form. The closest noble gas to oxygen is neon (Ne, atomic number 10). For oxygen to go from 8 electrons (its neutral state) to 10 electrons (the state it wants to be in), it needs to gain 2 electrons. Should it succeed in gaining these 2 electrons, its charge will become (-2), because it has 8 protons and 10 electrons. Nonmetals will almost always *gain* electrons when they form ions, so nonmetals almost always form negative ions (anions)."

Same here. Oxygen is not really an Ion in compounds where it has this oxidation number (i.e. -2). THIS is merely a 'formal' value. Oxygen is not an Ion in Silicate (SiO2) or in carbon dioxide (CO2) even though it has 'formally' taken two electrons from the other elements.


"Visually, those elements on the right side of the periodic table (nonmetals) have to move to the right (by gaining electrons) to become noble gases. Gaining electrons turns them into *negative ions*."

They do not become noble gases, for that they would have to undergo a NUCLEAR reaction. (!!!) They reach a noble gas electron configuration which is not stable (!!!)

The Shee, please, somehow, I felt attacked by your post, like as if my entry omitted a lot of facts. Don't do that again, contact the author first if you want to include extra info. Especially when you are not absolutely sure about what you are writing.

Thanks,

H

I'm sorry Hell. It isn't attacking you, but it is something that I wanted to put down... And of course it is oversimplification; there is nothing that can't be, in science! (not an attack either, just something I perceive) There is *always* exceptions, or another layer deeper to go, or more theories, etc etc etc... Sometimes we haven't found or come up with them yet, either, so please don't call me on that.

I most definitely did *not* want to attack your, or your entry, or *anything* like that. Excuse it, please.

--Shee

No problem Shee, I already thought that this was not your intention.

But if you want to provide additional info, make sure it is accurate, even if it is a simplification. In these cases it is perhaps better to contact the author or to pose questions and not banging info out stright away...

I agree that one of the most annoying things in science is this going through layers of detail business. Sometimes - for a didactic purpose - a simplification or a slight inaccuracy will do the job a lot easier and still get the correct picture across.

Bye,

H

Well, I did think that the "periodic table" bit did make the simplification more obvious to those who care and/or know enough to recognise it, but this isn't the problem, is it now?... i could have written something that used oxidation numbers and electronegativity too, but... Never mind. It just isn't worth it.

Yes, of course... I'm sorry; I wasn't thinking about this and its relation to *you* or to politeness, or to factuality, or to anything, really, at all. Oops.

Slight inaccuracies are all we've got... Some are more slight than others though, so... Eh, now my mind is getting off of science and onto its flaws, so I will stop.

Peace,
Shee

*Yikes*...

*sigh*

Not quite sure what I was thinking right as I posted that, either... I've been sort of scattered today... Please excuse me once again.

Hey... No problem. I am not angry, you must not excuse yourself.

Now *I* am starting to regret my remarks.

Excuse *me*, now.

H

Yikes... Why don't we just call this conversation quits? I respect you very much and quite understand where you are coming from.


Shee

(You are, of course, excused. )

Do you *really* understand where I am coming from? Tell me...

H

To have spent time on two different entries, one of which has a comment that came off wrong and wasn't very polite to put down in the first place, and then to not have *your* entry, which is in the h2g2 system therefore should be linked to, not be linked to... I would be quite miffed and upset myself, should it all have happened to me, especially at the exact same point in time.


However, in terms of actually *having* any type of experience like this, I have not... My edited entries (and the ones in PR and waiting for PR) are generally very very concentrated in a single specific area, which almost no one knows anything about and no one really comments on.


I should have said earlier that it really is a good entry... I'm afraid I haven't mentioned that.

OK I'll go take a glance at your entries, Shee.

See you there,

HELL

*starts to laugh a bit*

I hope that you didn't take that as a not-so-indirect hint?? That's not how it was meant... Oh well.

Peace.
--Shee

Well, it's my job anyways...

HELL