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)

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)