Talk:Chemical elements

If this is just to be an alphabetical list of elements, it looks more or less complete to me --Larry Sanger 09:52, 17 March 2007 (CDT)

I would prefer to prefix the atomic number and to see three columns (of lengths of about 37 entries): from Actinium to Gallium, from Germanium to Potassium and from Praseodymium to Zirconium (or close to this division). Is there somebody who can do this easily? --Paul Wormer 08:06, 27 October 2007 (CDT)

I put in a new HTML table (kept and commented out the old one). --Paul Wormer 09:12, 29 October 2007 (CDT)

• I removed the old list that I commented out earlier and added a list sorted on atomic number.--Paul Wormer 10:29, 9 November 2007 (CST)

Molecules

The sentence:

All matter around us (solids, liquids, and gases) are made up of atoms, either of one species (an element) or a combination of species (e.g., molecules, alloys).

strongly suggests that a molecule necessarily consists of different elements. This is not true, of course, H₂, N₂, O₂ are counterexamples.

Also I'm not certain that I agree with the definition "an element is a substance". The term "substance" implies a form of stability. However, when we speak of "elemental hydrogen" we don't mean H₂, but atomic hydrogen, which is highly unstable. Personally I would not call elemental hydrogen a "substance".--Paul Wormer 05:00, 12 June 2009 (UTC)

Chemical elements

Following text moved from discussion page of User:Milton Beychok--Paul Wormer 10:48, 15 June 2009 (UTC)

Hi Milton, addressing you as a chemistry editor I like to know what you think about Elements. Or, more specifically, about the definition: "an element is a substance with unique physical and chemical properties".

When I think of a substance I think of a crystal, or a liquid or gas consisting of molecules. Take the simplest element, hydrogen. It exists as a gas of molecules, a (cold) liquid consisting of molecules, different kinds of crystals also consisting of molecules, and probably (although never found yet) a metallic lattice of H-atoms. And as you know, hydrogen chemisorbed on the surface of a transition metal catalyst (like nickel) exists in atomic form. Now which of these substances is the element hydrogen?

Let me make the analogy with the alphabet: there are 26 letters, but a letter is not a word or a sentence. There are ca. 100 elements, but an element is not a molecule or a solid. Some words consist of one letter, some molecules consist of one atom (noble gases). In my view the definition "a letter is a word with a unique meaning" corresponds to "an element is a substance with a unique property". I find both definitions wrong. What is your opinion? --Paul Wormer 05:41, 13 June 2009 (UTC)

Paul, before I can respond meaningfully, what definition would you propose as an alternative? Than I will try to respond tomorrow, because I'm on way to bed right now. Milton Beychok 05:55, 13 June 2009 (UTC)

Hope you had a good night sleep when you read this. I wrote an earlier version of the article and in the meantime I didn't change my mind. If you go back in the history of Elements you see what I had to say about it. In short: atomic species of which there are 94 naturally occurring and about 20 man made (the latter are short-lived, don't form molecules, and are observed only as signals on a measuring device, would you call them substances?). Maybe the analogy with letters in the alphabet would be helpful? (I thought of it just today).--Paul Wormer 07:10, 13 June 2009 (UTC)

PS I gave it some more thought: Crucial, of course, is the meaning of "substance". Would one call diamond and graphite the same "substance"? If not, how does one define the element carbon? Would one call an artificial nucleus that lives 1 microsecond (as those with Z > 100) a "substance"?--Paul Wormer 13:34, 13 June 2009 (UTC)

(unindent) Paul, my first suggestion is that the article be re-named "Chemical elements" and that would avoid the need for a disambiguation page which would eventually arise.

Since you and Anthony Sebastian are the two most recent contributors to the Elements article, and I liked many aspects of both versions of the introduction, I decided to try and write an introduction that sort of merges what the two of you wrote. I also tried to use simpler wording and to avoid being too pedantic (I hope). My suggested wording is in green font:

In chemistry, elements are types (or species) of atom. All solids, liquids and gases are composed of atoms, either of one species or a combination of species.

There are 94 different elements (or atomic species) that occur naturally on Earth and each element has its own unique physical and chemical properties. Some elements are very abundant. For example, water is composed of the elements hydrogen and oxygen and water is very abundant on Earth. As another example, the element carbon is an important part of all animal and plant life on Earth as well all of the fossil fuels (natural gas, petroleum and coal) which are the remains of plant material that once lived.

Some of the 94 elements are very rare on Earth such as the gas neon. Some elements are stable and live for very long times while some, known as the radioactive elements, have finite life times and decay into other elements while emitting radiation. For example, plutonium is a well-known radioactive element.

In addition to the 94 elements that occur naturally on Earth, about 23 other known elements that do not occur naturally on Earth have been man-made and are characterized by having very short life times and being radioactive.

[I believe there are 118 known elements but I thought one of them has not yet been synthesized. Thus, 117 - 94 = 23 man-made]

I suggest that the next paragraph should begin with these words:

Each of the elements is distinguished by its unique integral number Z, known as the atomic number. The number Z is .... (without using the expression "we recall")

I also suggest that atomic isotopes and allotropes also be discussed somewhere in the article.

Also, regarding the quote from Aristotle at the top of the article (what Anthony called an epigraph), it is a bit too "artsy" for my taste and I would prefer to remove it ... but that is just my personal opinion.

I would like to say that all of my comments above are simply my comments as a fellow author. They are not to be taken as decisions made as part of my role as a Chemistry Editor.

Finally, Paul, I suggest that you move all of the exchange of comments by you and I (here on my talk page) to the discussion page of the article. Milton Beychok 02:55, 14 June 2009 (UTC)

End moved text

I copied Milton's (green) text, rephrasing it a little, inspired by Anthony's text. Moved Aristotle's quotation down, added sentence about transmutation, allotropy, and about isotopes. Some remarks:

• Stable nuclei live as long as the universe. Unstable nuclei may live a very long time, for instance the half-life of 238-uranium is 4.46 × 10⁹ years.
• The people making new elements are (nuclear) physicists not chemists.
• I removed Calvert's (former) function. It is quite uncommon to give somebody's function when you refer to him/her.
• Shouldn't the two tables be moved to a subpage?

--Paul Wormer 11:59, 15 June 2009 (UTC)

Well done, Paul! I think it looks very good now. Milton Beychok 17:08, 15 June 2009 (UTC)

Great improvement

Paul, excellent work. Thanks to Milton, too. —Anthony.Sebastian 03:06, 16 June 2009 (UTC)

Still not happy

The first sentence (abbreviated) is:

Chemical elements are types of matter each composed of a single unique type (or species) of atom.

I'm still not happy with this definition. Solids, liquids, and gases are "types of matter". Hence the definition says: an element is a solid, liquid, or gas composed of a unique type of atom. It says, for instance, that a pure lithium crystal is an element, a pure hydrogen (H₂) gas is an element, solid hydrogen is an element, molten lithium is an element, etc. It excludes, for example: a water molecule consists of the elements hydrogen and oxygen (which for any chemist is a commonplace statement).

The point is that an element does not necessarily exist in pure form. It may happen that an element only occurs in compounds, i.e., chemically bound to other elements. Take iron; in nature it appears only in oxidized form, as iron ore. Mankind made a great leap when it invented how to reduce the ore to pure iron. Wasn't iron a chemical element before Iron Age? --Paul Wormer 08:05, 27 June 2009 (UTC)

Paul, in response to your comments, to avoid ambiguity, I rewrote the first sentence of the Intro as follows:

Chemical elements — "the substances from which everything tangible is made"[1] — are those particular types of matter each of which is characterized by its composition by a single unique type (or species) of atom.

I edited the remainder of the first paragraph to read:

On Earth there are 94 different naturally-occuring elements,[2] and therefore 94 different naturally-occuring atomic species, each element having its own unique set of physical and chemical properties. Typically, elements are found in nature in the form of populations of atoms, often mixed with other elements.

I will change the last sentence, in response to your last point, to read:

Typically, elements are found in nature in the form of populations of atoms, often with the atoms of other elements or the selfsame atoms as compounds (e.g., oxygen gas, a population of compounds each of two oxygen atoms; iron ore, a population of compounds each of iron and oxygen atoms) or as mixtures.

Thanks for the challenges. Anthony.Sebastian 20:46, 27 June 2009 (UTC)

Since my above note, I further tweaked the Intro. Anthony.Sebastian 20:43, 28 June 2009 (UTC); and again Anthony.Sebastian 21:30, 16 July 2009 (UTC)

Recognizing elements?

Since the distinction is not made between elemental forms and compounds, I worry that fluorine would be the last element someone would ever recognize. Howard C. Berkowitz 02:30, 14 July 2009 (UTC)

Good point. I'll remove. Though when I ask my non-scientist friends whether carbon figures into their everyday life, they often mention global warming. Anthony.Sebastian 03:58, 14 July 2009 (UTC)

"Diamonds are a girl's best friend" Howard C. Berkowitz 21:52, 16 July 2009 (UTC)

The article's first sentence is hopelessly convoluted

Anthony, with all due respect, that first sentence is hopelessly convoluted. Here it is:

<blockquote.>Chemical elements' — "the substances from which everything tangible is made" — are those particular types of matter of which a sample of each element type is constituted of a population solely of a single type (or species) of atom — each element type unique in virtue of the number of protons in each of its sample population's constituent atoms' nuclei, referred to as the atomic number, symbolized Z, of the element type.

In my opinion, it needs to be completely scrubbed and re-written in a much simpler, more grammatical and much shorter language. Milton Beychok 04:24, 17 July 2009 (UTC)

It probably just needs to be split into multiple sentences. Here's my attempt, sans citations:

Chemical elements are the building blocks of matter, "the substances from which everything tangible is made." Each element type is constituted by a single type of atom, distinguishable from other elements by virtue of the unique number of protons in each atom's nucleus. Thus, each element has a unique atomic number, symbolized Z.

--Joe Quick 12:58, 17 July 2009 (UTC)

It became pure gibberish to me after about the second "of which" -- geez, I don't think I've ever seen a more impenetrable sentence! Hayford Peirce 15:43, 17 July 2009 (UTC)

"predated introduction"

That's a *lot* better! But what the devil does "predated introduction" mean? To me, nothing at all.... Hayford Peirce 20:03, 17 July 2009 (UTC)

Well done, Eaux Noble Rheaux! That actually makes sense now! Hayford Peirce 21:59, 17 July 2009 (UTC)

Ta, myte. Ro Thorpe 22:09, 17 July 2009 (UTC)

Explaining my revisions to the lead-in paragraphs

For the reasons expressed above by myself, Joe Quick and Hayford Pierce, I split the first two paragraphs into three pragraphs and reworded them to for clarity and grammar. I also removed the superscripted atomic numbers from the element (e.g., revised He² to He) because that introduces a convention that is not explained in the article and which most lay readers are not conversant with.

In-line references are meant to provide relevant documenting sources. They are not meant to include an exceedingly lengthy publisher's description of the book. Nor are they meant to include exceedingly lengthy verbatim quotations for a source. Therefore, I revised the references accordingly.

Reference 1 (Atkin's book) included a hyperlink to "Basic Books" which is broken ... so I deleted it. It really isn't needed since Reference 1 has a hyperlink to the full text of the book.

One note was included that was replaced by a CZ link (e.g., the note defining "matter" was replaced by the CZ linking of matter). After all, that is the primary reason for CZ linking. One other note (defining the word "sample") was deleted because that is a common word that really does'nt need a definition or a CZ link.

I think that covers almost all of my revisions. Milton Beychok 20:26, 17 July 2009 (UTC)

Hayford, I changed "predated" to "dated", is that better? Milton Beychok 20:26, 17 July 2009 (UTC)

Yes, that's a lot better -- now I understand it. But isn't there a better word than "introduction"? To me that means a brief couple of words in front of something else.... Hayford Peirce

Anthony, your reworded sentence: "This modern definition replaces that which predated the introduction by John Dalton of a quantitative atomic theory, which defined an element as a substance that neither ordinary physical nor chemical methods can decompose into simpler substances." is still far from understandable. Can you please re-write it so that is it crystal clear? Milton Beychok 21:34, 17 July 2009 (UTC)

Ro, I am not sure that your revision is what Anthony means. He may be referring to the definition that existed before John Dalton conceived his quantitative atomic theory. It would be most helpful if Anthony joined this discussion and helped explain what he means before any further changes are made in the article. Milton Beychok 22:11, 17 July 2009 (UTC)

Yes, indeed, I had it the wrong way round. I hope it meets with Anthony's approval now. Ro Thorpe 23:17, 17 July 2009 (UTC)

Reiteration of my point of view

I explained this before, but I don't like the statement that an element is a kind of matter. There are two kinds of matter: the physicist's (quarks, electrons, mesons, etc.) and the chemist's (solids, liquids, gases, and hybrids, such as liquid crystals and fluids above the critical point). An element is neither of the two. Since I get tired of this article, I won't say more about it and let it pass. Don't ask me for approval, though. --Paul Wormer 07:08, 18 July 2009 (UTC)

Paul: When you write, "…. I don't like the statement that an element is a kind of matter", you disagree with Linus Pauling, who wrote: "A kind of matter consisting of atoms that all have nuclei with the same electric charge is called an element (General Chemistry). Nevertheless, whether or not it makes a difference, I used the word ´type´, inasmuch as the ´type-token´ distinction is well-established.

More modern chemists, such as Fred Senese, continue to refer to elements as types of matter: "An element is a type of matter composed of atoms that all have exactly the same positive charge on their nuclei."

When I read chemists writing that an element is a ´type´ of matter, I interpret ´type´ as meaning entities having in common characteristics that distinguish them as a group or class. Given that matter refers to anything that has mass and occupies space, that interpretation would allow for many different types of matter, not just two.

For example, U.S. coins, which qualify as matter in virtue of having mass and taking up space, come in many types, such as the different U.S. State quarters, each collection of a particular State quarter having common characteristics that distinguish them as a group. Each State quarter constitute a type of matter, a type with many ´tokens´, viz., all the individual quarters (coins) of the type, the Texas State quarter type, say.

Chemical elements obviously qualify as matter, and in keeping with the above formulation, they certainly come in types — 94 naturally-occurring types, wherein all samples of each type (e.g., all samples of potassium) have common characteristics (e.g., atomic number) that distinguishes them a group, the definition of a type.

That line of reasoning led to my offer of this definition of chemical elements:

Chemical elements — "the substances[1] from which everything tangible is made"[2] — are those particular types of matter[1] of which a sample[3] of each element type is constituted of a population solely of a single type (or species) of atom — each element type unique in virtue of the number of protons in each of its sample population's constituent atoms' nuclei, referred to as the atomic number, symbolized Z, of the element type.[4]

No other type of matter — U.S. State quarters, iron ore, pure water, identical steel or plastic ball-bearings, etc. — is constituted of a population solely of a single type (or species) of atom.

I submit that explicating chemical elements with ´type of matter´ terminology is not fatal and has didactic value.

Paul, I hope you will give further consideration.Anthony.Sebastian 22:18, 18 July 2009 (UTC)

After reading most of the arguments I tend to agree that "type/kind of matter" is not a good expression. I never before thought about defining "element", so I do not have a suggestion. But O₂ and O₃ are two different forms consisting/made of the same element, thus the "element" is some sort of abstraction(?), not matter itself.
That (even well-known) chemists use an expression (e.g. when addressing fellow chemists) does not prove that it is suitable for a definition in an encyclopedic article that must define its terms precisely and unambiguously. Of course, if this definition is likely to look strange for a non-chemist, its significance should be explained, as well.
Peter Schmitt 00:43, 19 July 2009 (UTC)

Please see my Sandbox

I wrote two quick paragraphs that I think is preferable to the current intro, please look [here], and give me your thoughts. The two paragraphs may need to be reversed. David E. Volk 12:51, 18 July 2009 (UTC)

David, I like both your paragraphs. In particular, the points you make in the 2nd paragraph merit inclusion in the article. However, neither paragraph truly introduces the subject/concept of 'chemical elements'. We need to think of an audience somewhat naive in chemistry, at least for the Intro.

I do not find the lead sentence of the current version of the article especially helpful in that regard: "Chemical elements are those particular types of matter that serve as the building blocks of all other types of matter." It seems more of a teaser. The first sentence should be more inclusive, more definitive. Anthony.Sebastian 00:25, 19 July 2009 (UTC)

The first sentence is not at all a good replacement: "The 94 naturally occuring chemical elements each have, by definition, a certain number of protons (Z)" It assumes knowledge of protons (which is more advanced than element), and the elements do not have a number of protons "by definition", but rather they are classified according the number of protons in their atoms. Peter Schmitt 00:49, 19 July 2009 (UTC)

Look above at the version in green font text (June 14th) that Paul Wormer and I had agreed upon ... and for which Anthony said: "Paul, excellent work. Thanks to Milton, too" (June 16th).

Perhaps that version needs to be re-visited. I don't know how that version somehow got transformed into the current version. Milton Beychok 01:23, 19 July 2009 (UTC)

It would really be helpful to STOP revising the lede until it thrashed out here on the Talk page. Otherwise we have a moving target.

I think it would be most helpful to STOP revising the lede until some sort of concensus is reached or until a Chemistry Editor makes a ruling. Every time I look at it, it has changed again. Trying to discuss and agree upon a moving target is too difficult. Milton Beychok 01:57, 19 July 2009 (UTC)

Suggested lede

Milton, following your previous note, I suggest:

Chemical elements are those particular types of matter that consist solely of a population of a single type (or species) of atom, as exemplified by a wire made solely of copper atoms, say, or a sheet made solely of aluminum atoms. It follows then that the number of Earth´s naturally occurring types of atoms, established as 94, determines the number of Earth´s naturally occurring types of chemical elements, of which copper and aluminum are just two examples. The distinguishing characteristic of the 94 naturally occurring atom types is the number of protons in the nucleus of the atom, referred to as the atomic number, symbolized Z.

The atoms of the chemical element hydrogen, Z=1, have the fewest number of protons, and those of the element plutonium, Z=94, have the greatest number of protons, among the naturally occurring elements.

As protons each carry a positive charge, Z gives the positive charge of the nucleus in units of the so-called elementary charge, symbolized e. It is known that Z electrons (of charge −e, or negative e, and of mass much smaller than the proton) "orbit" the nucleus of an atom, so that an atom as a whole is electrically neutral, with its mass concentrated in the nucleus.

Anthony.Sebastian 02:14, 19 July 2009 (UTC)

Anthony, leaving aside for the moment Paul's dislike of the word "matter" which is a major point that must yet be resolved:

• "It follows then ..." : That does not make sense to me. Nothing in the first sentence proves that "it follows then ..."
• "Sheet" : what kind of sheet? A paper sheet? A plywood sheet? A bed sheet? Or a metallic sheet?
• "... referred to as the atomic number, symbolized Z." :As I have pointed out before, "symbolized" is not needed. It reads just as well if it is written very simply as "... referred to as the atomic number, Z."
• "...94 naturally occurring atom types ..." : Change to "...94 naturally occurring types of atoms ...". Would you not say "types of apples" rather than "apple types"?
• "...in the nucleus of the atom, ..." : Should that not be written as "... in the nucleus of the various types of atoms, ..." ?

Admittedly, these 5 items are rather trivial compared to the major point that must be resolved between you and Paul. But taken as a whole, they do indicate (at least to me) that more thought must be given the wording to be sure that the sentences are precise and accurate as well as clearly understandable. Milton Beychok 02:51, 19 July 2009 (UTC)

Milton, I have rewritten my suggested lede to respond to your comments. I appreciated your feedback.

Chemical elements are those particular types of matter that consist of a population solely of a single type (or species) of atom, as exemplified by a wire made solely of copper atoms, say, or a roll of kitchen foil made solely of aluminum atoms. The number of Earth´s naturally occurring types of atoms, established as 94, determines the number of Earth´s naturally occurring types of chemical elements, of which copper and aluminum are just two examples. The distinguishing characteristic of each of the 94 naturally occurring types of atoms is the number of protons in the nucleus of its atoms, referred to as the atomic number, Z, unique for each type of atom and for each of the corresponding chemical element.

Among the 94 naturally occurring chemical elements, the atoms of the element hydrogen, Z=1, have the fewest number of protons, and those of the element plutonium, Z=94, have the greatest number of protons.

As protons each carry a positive charge, Z gives the positive charge of the nucleus in units of the so-called elementary charge, symbolized e. It is known that Z electrons (of charge −e, or negative e, and of mass much smaller than the proton) "orbit" the nucleus of an atom, so that an atom as a whole is electrically neutral, with its mass concentrated in the nucleus.

Anthony.Sebastian 15:58, 19 July 2009 (UTC)

As I said before, the major point about using the word "matter" remains that you must resolve with Paul Wormer and with David Volk as well. But, please, no more unilateral changes to the article until that point has been resolved here on the Talk page. Milton Beychok 18:08, 19 July 2009 (UTC)

We now have 'Some particular types of matter, referred to as chemical elements...' which suggests that other types may not be chemical elements, somewhat misleading even if literally true. The CZ definition, however, has 'Atomic species...'; would that be better? Ro Thorpe 21:19, 19 July 2009 (UTC)

——Ro, I agree. See changes I made, working in sandbox: http://en.citizendium.org/wiki/User:Anthony.Sebastian/SebastianSandbox/Chemical_elements Anthony.Sebastian 02:38, 20 July 2009 (UTC)

And isn't "particular types" redundant? Every type of *anything* is particular to itself. Why can't we simply say, "Some types of matter etc?" Hayford Peirce 21:34, 19 July 2009 (UTC)

——Hayford, good point. 'Particular used for emphasis, but not required. Anthony.Sebastian 02:38, 20 July 2009 (UTC)

Why not take a broader view? This certainly is a core article addressed (also/mainly?) to general readers. Obviously it is difficult or even impossible to give a short, one-sentence definition of "element" which satisfies the experts and is easy to understand. But must it be one sentence starting (or containing) "element"? I think of something like (not well formultated, just giving the structure of what I mean):
"Matter consists of molecules, molecules consist of atoms. Atoms are the smallest building blocks that can be separated and identified by chemical reactions(?). Each type/species of atoms constitutes a chemical element. The chemical properties of an element are determined by their positive electric charge which is given by the number of protons in the nucleus. This number is called the atomic number of the element."
By the way, as a core article it should eventually contain more on the history than the short remarks made so far. And should the table better be moved to a Catalog?
Peter Schmitt 00:28, 20 July 2009 (UTC)

——I like your idea, but CZ guidelines ask for defn first sentence. I'll try to find link. Anthony.Sebastian 02:38, 20 July 2009 (UTC)

If anyone interested, I moved my approach to Intro to a sandbox: http://en.citizendium.org/wiki/User:Anthony.Sebastian/SebastianSandbox/Chemical_elements until issues resolved. Anthony.Sebastian 02:38, 20 July 2009 (UTC)

There you have: Chemical elements are those types of matter composed of a population solely of a single type (or species) of atom, as exemplified by...

But 'matter' is, as we have seen, controversial. How about simplifying to something like: A chemical element is a species of atom. Some objects, such as... consist of only one element, being made up only of a population of atoms of that element...

Continuing on to molecules, as suggested by Peter? Ro Thorpe 10:59, 20 July 2009 (UTC)

In response, I changed the lede pgraph there to read:

• Chemical elements are those types of matter — 'matter' defined here simply as anything that takes up space and has mass — that are composed of a population solely of a single type (or species) of atom, as exemplified by a segment of wire made solely of copper atoms, say, or a roll of kitchen foil made solely of aluminum atoms. Some chemists refer to chemical elements so defined as 'elementary substances'.[1] Others define a chemical element, without reference to the concept of 'matter', simply as a species (or type) of atoms, distinguishing species as described presently.[1] The distinguishing characteristic of each of the 94 naturally occurring types, or species, of atoms is the number of protons in the nucleus of its atoms, referred to as the atomic number, Z, unique for each type of atom and for each corresponding chemical element.[1] [2] The number of Earth´s naturally occurring types of atoms, established as 94, determines the number of Earth´s naturally occurring types of chemical elements, of which the examples of copper and aluminum represent just two.

Despite the controversial nature of 'matter', here we define specifically how we use the word, which incidentally chemistry textbooks frequently use in defining chemical elements. This version also raises from the footnote that some chemists define chemical element, without reference to the concept of 'matter', simply as a species (or type) of atoms. It would seem that might satisfy most commentators. Anthony.Sebastian 20:23, 20 July 2009 (UTC)

From the sandbox, but also in the main article:
"of a single type (or species) of atom, as exemplified by a segment of wire made solely of copper atoms,"
How should this example help to understand the meaning of element? One does not see or feel that copper is different (with regard to being an "element") from salt (or even bronze). If this were obvious, the elements would have been discovered much earlier. Peter Schmitt 11:30, 20 July 2009 (UTC)

When we say "as exemplified by a segment of wire made solely of copper atoms" we are saying, in the context of the sentence as a whole, that copper atoms represent a type or species of atoms and that a wire of only copper atoms exemplifies a chemical element. Anthony.Sebastian 20:47, 20 July 2009 (UTC)

Yes. 'A chemical element is a species of atom. Atoms are the smallest building blocks...' Ro Thorpe 11:57, 20 July 2009 (UTC)

Yes, Ro, a chemical element is a species of atoms, by one definition. But that's just one meaning of chemical element. The IUPAC states (see footnotes 1and 2) that two definitions of chemical element qualify as valid, the second, where chemical elements are sometimes referred to as 'elementary substances', means that a lump of pure iron or a wire of pure copper can 'exemplify' chemical elements. We must accommodate both definitions sanctioned by the IUPAC, and not fixate on just one, as you appear to be doing. Even WP gets the point, though you might not be able to tell from the poor wording. Pease re-read the revised lede pgraph above or in my sandbox, where I elevated the crux of footnote 1 on IUPAC's statement into the main text. Anthony.Sebastian 20:47, 20 July 2009 (UTC)

Here, the IUPAC defn 'chemical element':

• 1. A species of atoms; all atoms with the same number of protons in the atomic nucleus.
• 2. A pure chemical substance composed of atoms with the same number of protons in the atomic nucleus. Sometimes this concept is called the elementary substance as distinct from the chemical element as defined under 1, but mostly the term chemical element is used for both concepts.

Note the revised lede pgraph incorporates both. Surely you do not doubt that a segment of wire made solely of copper atoms is a "A pure chemical substance composed of atoms with the same number of protons in the atomic nucleus"? Anthony.Sebastian 20:56, 20 July 2009 (UTC

No, I don't. But I don't think it helps: it is like saying the tea I'm drinking would be a pure chemical substance if it didn't have milk in it. It's confusing the explanation of the thing with an example of it. Saying that this wire is pure copper & that one isn't doesn't help me understand what a chemical element is. Ro Thorpe 23:53, 20 July 2009 (UTC)

as exemplified by

When we say "as exemplified by a segment of wire made solely of copper atoms" we are saying, in the context of the sentence as a whole, that copper atoms represent a type or species of atoms and that a wire of only copper atoms exemplifies a chemical element. Anthony.Sebastian 20:47, 20 July 2009 (UTC)

Sure, copper is an example for an "elementary substance" -- but it does not exemplify the difference between an elementary substance and a composite substance. This statement on the second line of the introduction does not help to explain what an element is. First the concept should be explained. Peter Schmitt 22:57, 20 July 2009 (UTC)

Personally I would *love* to have a simple intro paragraph that makes clear the difference between say, a hydrogen molecule and a hydrogen atom, the relation between the two, and how, what, and which of them, say, is filling up a balloon. And to make clear how and what the difference is between a copper atom, copper molecule, copper element, and a copper wire. The wire, for instance, is it composed of all *three*, one within the other, as it were, like a Russian doll? (How on earth did I manage to sell dozens of stories over the years to Analog, the science-fiction magazine for hardcore engineers? Guess I could fake it pretty well, hehe....) Hayford Peirce 23:10, 20 July 2009 (UTC)

two definitions

As I see it, the "two definitions" are no problem at all (and even less contradicting). The first one says that an element is a "species of atom", the second says that the same word is also used as short for "elementary substances" whose molecules consist of atoms of one element only.
Therefore, the logical procedure is to define element according to the "first definition", and later to explain the second use of the word when (in contrast to elementary substances) composite substances are mentioned/explained.
Any discussion of and reference to further subtle differences or difficulties should be postponed until later in the text: The introduction should be simple.
(By the way, CZ:Article_Mechanics#Opening section only says "The first paragraph usually begins with a definition of the topic". It does not demand that "Chemical elements" are the first words, or in the first sentence. -- such a restriction would not be sensible, anyway.)
Peter Schmitt 23:18, 20 July 2009 (UTC)

Let's say that a couple of years of tradition have now made it at least a semi-official standard that the name of the article is always incorporated, in the same form, in the lede sentence. Frankly I don't see why any article at all can't be written this way - surely our native intelligence and keen ingenuity will guide our typing fingers as we figure out a way to do it.... Hayford Peirce 23:31, 20 July 2009 (UTC)

Usually -- certainly. But if things are easier (more narrative -- another CZ principle!) one should be "allowed" to not follow this practice. (The remark addressed my (vague) suggestion of an introduction in the middle of #Suggested lede above. There the topic to be defined appears on the second line (approx.) only. Peter Schmitt 23:51, 20 July 2009 (UTC)

Peter, I note that Encyclopedia Britannica Online, with bazillions of articles, usually manages to pull it off. Anyway, see next section. Anthony.Sebastian 01:31, 21 July 2009 (UTC)

Suggested new lede in response to above comments

In response to the above comments, suggest this lede:

'Chemical elements', in one sense of the term, refers to species, or types, of [[Atom|atoms Familiar species of atoms include oxygen, copper, gold, and mercury — among the 94 naturally occurring species of atoms on Earth. See tables below. The distinguishing characteristic of a species of atoms is the number of protons in the nucleus of its atoms, referred to as the atomic number, Z, unique for each species of atom and for each corresponding chemical element.

In another sense of the term,'chemical elements' refers to chemical 'substances', each composed of a population of atoms solely of a single species, or type, of atoms, again as distinguished by its atomic number. In this sense of a 'chemical element', sometimes the term 'elementary substance' is used instead, but most often 'chemical element' is used for both senses. Familiar examples of such 'pure' chemical substances are segments of wire made solely of copper atoms, and rolls of aluminum foil made solely of aluminum atoms. This second sense, or concept, renders 'chemical element' a somewhat more tangible particular, defining it in terms of a substance. 'Substance' remains undefined, but chemists typically define it in terms of matter, or imply matter, in its sense of something that takes up space and has mass. In particular they refer to substances having a definite composition, and often restricting them to 'pure substances' such as pure chemical elements or compounds, but not to mixtures of substances, such as alloys.

Anthony.Sebastian 01:34, 21 July 2009 (UTC)

Yes, that's looking a lot better, but why not begin, "Chemical elements, in one sense of the term, refer to species, or types, etc..."? It's a more robust opening. Hayford Peirce 01:38, 21 July 2009 (UTC)

Super. Will do. Made change, look again, above. Anthony.Sebastian 01:43, 21 July 2009 (UTC)

Looks good. But is the phrase singular or plural -- I think it could be argued either way. Hayford Peirce 02:17, 21 July 2009 (UTC)

The phrase is embraced by single quotes, rendering it 'mentioned' rather than 'used' in linguistic terminology, and it is appositionally referred to as a term, therefore I argue 'singular'. Anthony.Sebastian 02:42, 21 July 2009 (UTC)

Well, here is it again, the "moving target". One has to go back in history to understand the comments.
And - talking of "usual" introductions: It is not usual to embrace the term by quotes. :-) Peter Schmitt 10:08, 21 July 2009 (UTC)

Respectively, Peter, it doesn't seem appropriate to label continued editing for clarity, precision, and coherence as a "moving target", presaged by words of impatience. I believe everyone is sincerely trying to achieve a quality product. Anthony.Sebastian 17:57, 21 July 2009 (UTC)

Sorry, Anthony, this was not meant as an insult. "moving target" was taken from a remark by Milton a few days ago (see above), and should remind you that it is difficult to follow a discussion (as in this subsection) where you suggested a text and Hayford commented it, when you change the text instead of following up with a new version after this comment (so that one can easily compare the two versions). Peter Schmitt 22:42, 21 July 2009 (UTC)

You are right, Peter. Dumb of me. Check below, two lede pgraphs. I'm hopeful we can get consensus to at least put them on the Main Article as a start for collaborative work. I've tried to distill everyone's comments into two compact pgraphs. I'd like to end the Intro with them, put rest of material in sections to follow. See example at http://en.citizendium.org/wiki/User:Anthony.Sebastian/SebastianSandbox/Chemical_elements. Anthony.Sebastian 03:44, 22 July 2009 (UTC)

Another suggestion

Since it easy to criticize I also offer an attempt:

A chemical element is, in the narrow sense of the term, a species (or type) of atom, characterized by the number of protons — its atomic number — in its nucleus. In a wider sense, a chemical element or elementary substance is a substance which is composed of (molecules of) atoms of only one particular element.

The distinction between the two senses, or concepts, of chemical elements is not one of 'narrower' and 'wider'. It's more closely related to 'abstract'/'general' and 'concrete'/'particular'. I do not feel that narrower versus wider gives us any additional clarity or precision. Anthony.Sebastian 17:45, 21 July 2009 (UTC)

In contrast to that, chemical compounds are composed of two or more elements. Compounds can be decomposed by chemical processes into elements, elements can be combined or recombined to compounds. It is a characteristic property of elements that they cannot be decomposed any further by chemical processes.

There are 94 elements which occur naturally on earth. Familiar examples are oxygen, copper, gold, and mercury. Examples of elementary substances are a wire made from pure copper, or a foil made from pure aluminium. On the other hand, water is a chemical compound consisting of hydrogen and oxygen.

(I think that the definition of "substance" need not be discussed in this context because it may be understood in its informal sense.)

I think the discussion of 'substance' should be covered in a footnote. Anthony.Sebastian 17:45, 21 July 2009 (UTC)

A succinct lede that seems to meet the needs of most Talk respondents

From my sandbox: http://en.citizendium.org/wiki/User:Anthony.Sebastian/SebastianSandbox/Chemical_elements
NB: Suggest these two pgraphs end the Intro:

Intro

Following the convention of the International Union of Physical and Applied Chemistry (IUPAC), 'chemical elements', in one sense of the term, refers to species, or types, of atoms. The distinguishing characteristic of a species of atoms is the number of protons in the nucleus of its atoms, referred to as the atomic number, Z, unique for each species of atoms and for each corresponding chemical element. Familiar species of atoms include oxygen, copper, gold, and mercury — among the 94 naturally occurring species of atoms on Earth. See tables below.

In another sense of the term,'chemical elements' refers to chemical pure 'substances' each composed of a population of atoms solely of a single species, or type, of atoms, again as distinguished by its atomic number, Z. In this sense of a 'chemical element', sometimes the term 'elementary substance' is used, but most often 'chemical element' is used for both senses. Familiar examples of such 'pure' chemical substances are segments of wire made solely of copper atoms, and rolls of aluminum foil made solely of aluminum atoms. This second sense, or concept, renders 'chemical element' a somewhat more tangible particular, defining it in terms of a substance.

Dust is settling

I hope that the article is now close to convergence. Let me make a few comments on Anthony's version in his sandbox.

1. I see that IUPAC's first definition agrees with the one I wrote many versions ago (David Volk and Peter Schmitt suggested essentially the same definition). I notice that Anthony is finally convinced that that definition must come first.

2. I don't see the need for a reference to the IUPAC, it is clear from the previous discussion that any chemist agrees with the definition "an element is an atomic species" (or similar words to that effect). Also the quotes around chemical element don't serve any purpose. If we use them here, we must use them everywhere, as for example in: 'Taxonomy' is the science of collecting ...

3. Peter remarked that it is better to use "units of positive charge" instead of "protons". It could indeed be more pedagogical.

4. The second IUPAC definition is the one that Anthony had in mind all along and that I objected to. I had two reasons for this objection: (a) The existence of allotropes, e.g., what now is elemental carbon, graphite or diamond? (b) The fact that some elements may not exist in pure form at all. I gave the example of iron before the Iron Age. Iron did not exist in pure form before that time. I may add silicon (Si) before the semiconductor age, pure silicon is man-made. Having said this, I now recognize that the second definition is the lay person's definition and as such it deserves to be mentioned.

5. Except for the word "population" Anthony's second definition is OK. I don't like the word population in this context because it implies something that is populated. (In daily life it is often a piece of land, as in the "population of the Bay Area is 20% Latino"). In science for instance quantum mechanical states and adsorption sites are populated. So write simply: "each composed of a large number of atoms solely of a single species". "Population" is used a lot further down, IMHO in all cases misused.

6. Anthony likes quotes and underscores much more than I do. I learned from Donald Knuth (TeXbook) that in printed matter underscores are a no-no. I always write as if CZ is printed matter, but this is open to discussion. Does CZ have laws on this, constable Peirce? (Our law-enforcing officer doubtlessly knows the law).

Except for a few very minor things, Anthony's sandbox version is close to approval, especially when my remarks are taken care of.

--Paul Wormer 08:53, 23 July 2009 (UTC)

Just adding in my two cents; I don't know much about the subject. In general, underscores are discouraged. That being said, I didn't see a single underscore in Anthony's sandbox.Drew R. Smith 09:12, 23 July 2009 (UTC)

Paul talks about underlined words. Peter Schmitt 09:43, 23 July 2009 (UTC)

I agree with Paul. Some more remarks:

1. The letter Z for the atomic number is not used and not needed here.

2. Since "element" is defined by the number of protons, "unique for each species of atoms and for each corresponding chemical element" is a (circular) repetition. I think the sentence would be simpler and clearer without it.

3. Sorry, but I do not understand what the last sentence ("tangible particular") should tell me.

4. Paul: What is your opinion on mentioning the role of chemical processes in recognizing elements?

Peter Schmitt 10:20, 23 July 2009 (UTC)