Chemistry question

[jfribrg]

My 8th grade son is doing a report on Gold. You can say he is becoming an Authority on the element. One question he needs to answer is where gold is in the periodic table and why. Of course he had no trouble with the where part, but the why has been a problem. We did a little research and found that gold is one of the metals where more than one electron shell is not complete. The question is whether this is a characteristic of all the elements in the same column as gold (Copper and Silver), or is this characteristic of metals in general (in which case, how can Hydrogen under pressure be metallic), or of some subset. The main source we've used is this web site. Any input would be much appreciated.

[Fazor]

I thought that elements were grouped in order of atomic number (number of protons in nucleous)? I dunno tho I'm not really into chem much.
This or This might help.

[Tog]

I thought that elements were grouped in order of atomic number (number of protons in nucleous)? I dunno tho I'm not really into chem much.

That's how they got the order of them, but not the shape of the grid. The first row, Hydogen and Helium has one shell of either one or two electrons. A shell is like a planetary orbit except that it has not set plane, the lectrons just wander around at that distance.
The second row has two shells. The first has two electrons, and the second has 1 to 8, depending on the element. Each row gets a new shell, and in most cases, each of the inner shells must be full.
Most atoms like to have a full outer shell, so they combine with other atoms to do just that. Oxygen has 6 electrons on the outer shell, so it can either loose 6 or gain 2. Hydrogen as one, so wants to either gain OR lose one. When two hydrogen meet one oxygen, the electrons from the outer shells of all three atoms are shared to give the illusion of three atoms will full outer shells.
This "willingness" to lose or gain electrons puts them on either the left or the right side of the table depending on the preference. the ones that prefer to lose go tot he left, and the onse that prefer to gain go to the right. This is why there is a gap on the second row as opposed to even spacing like battlements on a castle wall.

At lest that's how I seem to recall understanding it. (see below for corrections)

As for why gold is where it is, on the off chance I ever did know, it's long gone.

[Fazor]

If you ask me, it's all just a popularity contest. (that's the kind of answer that i would have given, and explaines my low grades yet extreemely high test scores lol). From what I understand, the row is metallics, the collumn had something to do with number of...ermm...[someone correct me with propper term] possible orbits? or number of electrons or something. I thought i had a bookmark to a website describing it but i can't seem to find it. it was talking about electrons shifting from one level to another (creation of photons) but dealt with the periodic table somewhat. anyway, someone with more ed-joo-mah-kation can jump in anytime now.

[Tobin Dax]

I'm fuzzy on the details by now, but as I remember it, all of the elements in that column have that property. (I think that the same is tru for the column with chromium and tungsten as well.) The reason for this is likely High School-level, but, as I remember it, one set of orbitals in the next energy level has a lower energy than the last orbital of the second-highest energy level. Since electrons like to have as little energy as possible, they leave that second-highest level unfilled as they start to fill the next energy level.

Hopefully that's some help. There's gotta be someone around that can say this better than me, but that should be a start.

[Swift]

It is important to distinguish between the metals in the first two columns (like sodium) and the transition metals where gold is. In the transition metals, you are filling the d orbitals, which is key to their properties. When you get to gold you have this ground state configuration

[Xe].4f14.5d10.6s1

So gold has filled the 5d orbital and has an unfilled 6s1 orbital. Siliver above it is similar. This is part of the reason for the relative unreactiveness of gold.

[farmerjumperdon]

A person can learn more here by accident . . . .

[Tobin Dax]

Thanks for the electron configuration, Swift. I was too lazy and unsure to try to post it myself.

[snarkophilus]

One question he needs to answer is where gold is in the periodic table and why.

The facetious answer, of course, is that it has 79 protons, so it needs to go between numbers 78 and 80.

The real question you want answered, I think, is "why is the periodic table shaped the way it is?"

To expand upon what Swift said, "When you get to gold you have this ground state configuration [Xe].4f14.5d10.6s1," silver has the configuration [Kr].4d10.5s1, and copper is [Ar].3d10.4s1 . Because the outer electrons (called valence electrons) are similar, silver and copper will be very similar to gold in terms of physical properties. In fact, this is true for almost all columns of the periodic table: they have similar valence electrons, and it turns out that that means they have similar properties.

And that's the real reason why the periodic table is set up like that. Elements in the same column share the same electron configuration. Gold is under copper because they both have (n)d10 (n-2)s1.

Interestingly, the elements just to the left of gold, silver and copper have a s2d8 configuration: they fill the s orbital and leave a d orbital empty.

We did a little research and found that gold is one of the metals where more than one electron shell is not complete.

You are talking about how there are no electrons in the 6s orbital and the 5p orbitals (so the n=5 and n=6 shells are incomplete). That's true, but it's a bit misleading. Those p orbitals almost never come into play in most chemistry (sometimes, in biological systems, they are important). For transition metals, only the s and d orbitals are usually important (and f orbitals for lanthanides and actinides).

The question is whether this is a characteristic of all the elements in the same column as gold (Copper and Silver), or is this characteristic of metals in general (in which case, how can Hydrogen under pressure be metallic), or of some subset.

It is true of all metals except for those in the p block (last six columns) of the periodic table and Zn, Cd, and Hg. Lead, for instance, is only missing p electrons: all of its s and d orbitals are filled. Those in the first column have three not-completely-filled orbitals: the (n+1)s, (n+1)p, and nd orbitals. Lanthanides and actinides may also have at least three incompletely filled: f, p, and d (and sometimes s, too, making three incomplete shells).

You have to be careful using the word "metal" around astronomers, by the way. Some (many) of them regard any element that is not hydrogen as a metal, which is probably not what you mean at all! Hydrogen acting metallic is due in part to something really strange (called degeneracy pressure), but you can see that it's reasonable to assume that it might: it shares an electron configuration with the metals lithium, sodium, and potassium.

[Dr Nigel]

Yeah, what Swift and Snarkophilus said.

Additionally, the chemical properties of each element are defined by the energy transitions available to the orbitals of the outer electron shell, and also by the shape of those orbitals. However, my molecular orbital theory is a bit shaky, and my understanding is too limited when it comes to the transition metals.

You may also find this site of use:
http://www.chemsoc.org/viselements/index.htm

[Jeff Root]

Hydrogen is an oddball (as a result of its simplicity), making
it hard to compare with other elements.

The fact that there are more than two variables means that an
X-Y grid (the periodic table) cannot show all the relationships
between elements just by position within the grid.
The variables include:

- Proton number
- Neutron number
- Orbital types (s, p, d, f)
- Number of orbitals in each shell (2, 8, 8, 18, 18, 32, 32)
- Differences in energy levels between different orbitals
- Size of the atom or radical
- Electronegativity

I wrote what I think is a pretty good overview of the periodic
table for a glossary of terms used in genetics. I put several
entries from the glossary in my reply to the question asked in
the thread, "What Is The Table of Elements?":

http://www.bautforum.com/showthread.php?t=43940

Comments and criticism of those glossary entries are welcomed.

-- Jeff, in Minneapolis

[Swift]

<snip>
Those p orbitals almost never come into play in most chemistry (sometimes, in biological systems, they are important). For transition metals, only the s and d orbitals are usually important (and f orbitals for lanthanides and actinides).

A very small snit with that statement (everything else is "golden"). I wouldn't say P orbitals are "sometimes important in biological systems". P orbitals are not usually involved in the bonding of metals, but they are very important in non-metals and in lots of organic chemistry (such as double and triple bonds).

[snarkophilus]

A very small snit with that statement (everything else is "golden"). I wouldn't say P orbitals are "sometimes important in biological systems". P orbitals are not usually involved in the bonding of metals, but they are very important in non-metals and in lots of organic chemistry (such as double and triple bonds).

Yes, I agree. I was only talking about "those" p orbitals: that is, the ones in transition metals. P orbitals are pretty much always important in the organic parts of organic molecules.

Occasionally in metal-organic molecules you'll see some back-bonding into metal p orbitals, especially for those near the right hand side, and of course p orbitals are important for metals in the p block (e.g. lead).

[publiusr]

I'm really looking forward to super-chemistry--where molecules behave like atoms.

[Dr Nigel]

I'm really looking forward to super-chemistry--where molecules behave like atoms.

Erm .... what?

The key thing about atoms, right, is that they remain unchanged during chemical reactions (apart from the very outermost electron shell).

The key thing about molecules is, right, that you can, like, change them in chemical reactions. Yeah?

[01101001]

Erm .... what?

I guessing, but I think the prefix is important: super-chemistry.

Ultracold Molecules Could Benefit Fields of Superchemistry, Quantum Computing

The new form of matter that the Innsbruck University team produced in 2003 is called a Fermion superfluid, which exists only at temperatures hundreds of degrees below zero.
[...]
Cornell, Ketterle and Wieman created their Bose-Einstein condensate out of bosons, one of the two major categories of subatomic particles. Bosons carry force, while the other category of particles, fermions, comprise matter. Chin and the Innsbruck team showed in 2003 that, with some difficulty, fermions--in this case, lithium atoms--also can be coaxed into a Bose-Einstein condensate.

[Dr Nigel]

Oh, I see. So it's more the chemistry of a BEC than of atoms behaving as molecules per se.