Why does the VIIIB group have 12 elements?

Hi,
so I got this question that you can read above (it is about the periodic table and its groups). When I was trying to find the answer I basicaly bumped only on one page that explains it. It is important to note that this system is old one and nowdays you only number these groups from 1-18. If you want to read the answer from first hand go here: 1)

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So in the new system they are not in the same group, but why were they there before?

The groups are made by comparing the physical and chemical characteristics of the top electron shells. This special VIIIB group are the collumns under Fe, Co and Ni which makes it quite unusual.

Basicly as you move across the periodic table, different oxidation states are more and more stable (in chemistry most things just want to get as stable as possible).

Those elements that have similar stable oxidation states are then put together. Take for example halogens. Those are the very very reactive elements next to noble gases.

Halogens in periodic table.

All of them will have oxidation number -I (most of the time). This puts them together. Transition metals are much more difficult to grasp with their d-orbitals. As you have seen in my other post they make some problems. The oxidation numbers for them are not very clear. Iron can be in II as well as III but generally these twelve/nine elements are occuring in the similar ones. Oxidation for these elements is actually almost always 2 or 3, this is especially true for nickel.

Dragallur

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Huge mistake in valence electrons

Hi,
finally today I am going to explain the huge mistake in valence electrons of most metals. This is a mistake that I guess that most teachers learn and you will find it all around the internet, if it is not there then it is probably not explained accurately.

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When people usually write out the electron configuration of atom or ion they use the quantum number of the atom to get it and then it depends if the atom is in s,p or d part of periodic table.

s,p,d,f elements

Those atoms have valence electrons in the respective orbitals.

Oxygen for example is p-atom. It is in second period so the highest orbitals will have the number 2. All p-atoms have full s-orbitals and oxygen has four spare for p-orbital.

O: [2s]2 ; [2p]4 (lets write it like this, four electrons in p-orbital and two in s.)

This is the usuall way and it works quite well, except when it does not.

The problem comes with transition metals (which is most of the table), those are metals in the d-group, the ones in the middle. Particularly you will see the mistake with 6th and 11th collumn. If you would write the configuration for Chromium for example it should go like this:

Cr: [4s]2 ; [3d]4 (d-orbital is always -1)

But whoops! There is mistake! Why? Because you are assuming that the energy of the orbitals continues to go like this, that 4s orbital has lower energy than 3d. This happens not to be true in this case, generally the difference is very small, the nucleus changes as you add protons and neutrons to it which may change the balance. Now in this case it does change the balance, I do not understand the mechanics behind it so you will have to deal with this. The right configuration of Cr is this:

Cr: [4s]1 ; [3d]5 (the number of electron remains the same)

Also 4s is close so it is not very stable to put there one more electron when you have nice free 3d orbital.

This problem occurs again with molybden but not tungsten and seaborgium! This is because the effect is not strong enough, the atom looks different and so on. As I mentioned this mistake is also in 11th collumn which is copper, silver, gold and roentgenium. These guys have full d-orbital and only one electron in s-orbital.

Of course if you create ions you will bump into this again. Vanadium which is right next to chromium has the problem again,

V^{5+ ;} V⁴⁺ 3d^{1 ;} V³⁺  3d^{2  ;}  V²⁺  3d^{3 ;}  V⁺  3d^{4  ;}  V   3d³4s²

Sometimes this whole problem is explained as that d-orbital is more stable when half full or full completely. This is false since clearly it does not explain tungsten which behaves normally.

If you get to write configurations of transition metals check out this page, it will show you exactly how it looks like and you wont do mistake. Also I used these pages for the answer so check out these if you are not sure about something: 1) 2)

Dragallur

How radioactivity was studied

Hi,
today I want to write about radioactivity. It is rather new concept which is not very surprising as the process of radioactive decay is not very visible and the effects (on health for example) are not so clearly connected since they usually have long time span. Probably largest work done on this topic was by Marie Curie and her husband Pierre.

This is how radium dials looked like, cute!

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Curie was from Poland. She had kind of difficult childhood since women were persecuted at that time in the east and it was hard for her to find place to study. Later on, she was able to move to Paris with her sister. There she met Pierre with whom she had two kids.

The first time she encountered with radioactivity was when she measured pitchblende [1] and uranium and how much radioactivity they  were “giving off”.

She expected that pure uranium would be much stronger but this was not what happened, what she found was exact opposite. Later on, thanks to this she found out two new elements: Polonium and Radium.

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At this time it was not yet known that you can get pretty easily cancer by being close to radioactive stuff. Curie and Pierre were buying tens of kilograms of pitchblende to do their research and prove those two new elements since lot of other scientists were kind of sceptic about it.

In November of 1898 they extracted compound that was 900x more radioactive than uranium, you can see where this was going.

In 1902 it was announced that one decigram of radium chloride was succesfully isolated.

Four years later Pierre died when wheel of carriege run over his skull, this was because of the effects of radioactivity, at this point he was not really able to use his hands, they were pretty much destroyed by the pitchblende and his whole health was in very bad state.

In 20′ it started to be more and more clear that there is something wrong with the stuff. There was actuall factory that painted dials with radium (not pure of course), this is because it glows nicely and everyone liked it. The brushes that were used for this had to be kept sharp and this was done by lips. For this work about 4,000 people were hired, the so called “Radium Girls” was a group of women that also painted for fun their nails, face and teeth, noone knows how many sacrifices this caused.

Dragallur

[1] Pitchblende is mineral that is radioactive since there is uranium and other heavy elements. Lot of miners in extreme conditions died because they were mining it.

Island of stability for dummies!

Hi,
island of stability is an area surrounded by lot of really fast decaying elements. Today I will write about island of stability which is on the other hand area with hypotheticly and relatively stable elements.

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By area I do not mean some place. It is rather area in periodic table of elements extended for various isotopes.

The more heavy nucleus of atom gets, the easier and better for him it is to decay, potentially killing everything around, or at least giving some nice brain tumors. But then at some point, some of the elements are smart enough to stay stable, like a boss. Those are the elements in island of stability, this island is not very big and we can just guess its highest peaks.

The elements are much more stable because of the shape of their nucleus. The problem is that the nucleus becomes a bit deformed, even elliptical.

Anyway there is this thing called “magic number” which is a number of protons or neutrons which can lead to good shape which is stable, this means round normally. Such numbers are for example 2,8,20,28… 126. There are few other hypothetical (196,236…), elements which live on this island should have some combination of these numbers which would make them much much more stable than the stuff around.

For example Ununoctium which is the last known element has half-life of only 890 microseconds.

The island should come in proton number of roughly 120 and little bit more.

Picture showing the island of stability (white circle). The most stable elements could last for longer than an year.

There is even hypothetical second island. It would have to be around element 164. Who knows how many more theoretical elements there are before we will simply not be able to stick all these protons and neutrons together (not that we are sticking them).

Dragallur

 

 

Elements of Periodic table: 4) Selenium

Hi,
why Selenium? Well I was not sure what element to choose, I did not want to write about some precious metal since last two time I have covered gold and palladium. I used random generator and I got 34, which is proton number of Se.

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History

Selenium is one of those elements which were find in last centuries. This usually happens because the element is not enough common for some alchemists to find it or it is always well bonded with other element (here it is sulfur) and it took some time before we were able to extract it.

Jöns Jakob Berzelius and Johan Gottlieb Gahn were chemists in Sweden and they were working close to Falun mine [1], which you can see on the next picture. 

Guys there wanted to know what was it what they mined so they gave sample to those two chemists. It seemed to be some kind of arsenic compound but it was smelling strange and soon they found out that it is similar to sulfur and tellurium. Tellurium was named after Earth so they named Selenium (in Greece) after Moon, this happened in 1817.

Occurrence

• Universe: 3.0×10^-6 %
• Earth’s crust: 5.0×10^-6 %
• Ocean: 4.5×10^-8 %
• Human: 5.0×10^-6 %

You see it is not very common, at least it does not seem to be. But if I compare it’s occurrence in Universe with other elements it is not so bad. Most metals have one or two magnitudes less occurrence, from what I found selenium is not produced in solar fusion which means that it is created from supernovas, which would explain it’s  relative rarity.

On the picture above you can see some Se in piece of sandstone from uranium mines.

Usually you will find it with sulfur so you need to extract it using methods as SX/EW [2].

Properties

Se is non metal element which can exist in several allotropes [3]. 

It is usually red powder as you can see above but if you melt it rapidly you will get this kind of grey form which is usually sold. Se makes big and complex structures.

There are five Se stable isotopes and the couple of others with half life ranging to thousands of years, than there is Se 82 which has half life of 10^20 years which is considered relatively stable.

It has extremely important property of photo-conductivity, its conductivity depends on the amount of light hitting its surface.

Selenium is toxic element.

Usage

Selenium dioxide has a great usage during manganese electrolysis because it decreases the energy needed to get manganese (it works as catalyst). China is largest consumer of this compound for such use. For ton of manganese there are two kilograms of Se used. There are 31,200,000 tonnes of manganese produced each year.

Glass gets often kind of yellow or green color because of iron or other things accidentally mixed into it so Se is used to color it into red, this is the most common usage.

Also since lead is so toxic Se is used in brass with bismuth. At low concentrations it also improves machinability of lead, which is similar usage as of vanadium which improves the strength of steel.

Because of its photo voltaic property, it is used in photo voltaic cells called CIGS (copper indium gallium selenide solar cell).

There are other trace uses like radiography.

On the pie graph you can see the production of Se. While I did not find the graph of biggest consumers of Se, on the top is clearly China, as always.

Selenium in organisms

Organisms need selenium as we found out. It is important in some cellular processes but only really small amount like tens of micro grams.

At one time people thought that it is going to be good if they get more Se through some pills. Soon it was found out that more than 200 micro grams can cause cancer and so on. More accurately in one test, doctors got their patients 17% higher chance of prostate cancer which is number two of cancers killing male humans.

There are some illnesses with the lack of selenium but they are not very common even in places where is small amount of Se in the soil like New Zealand.

The price for Se is about 60$ for pound while at some times it lowered to about 30$.

Dragallur

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[1] Falun mine was extremely important mine producing 2/3 of Europe’s needs of copper. It was working for almost 1,000 years and it is now cultural heritage with museum.

[2] SX/EW (Solvent extraction and electrowinning) is method used to get some metals like nickel, cobalt, zinc and uranium.

[3] Allotrope of carbon is for example graphite and diamond, both made up of only carbon but with different shape of molecules.

Elements of Periodic table: 3) Gold

Hi,
it is probably one of the best known metals in the world and even throughout the history. Humankind knows it for a long time. It is precious metal with amazing properties from conductivity to ductility. It does not react so much which means you can actually eat it pretty easily!

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Right, we are talking about gold, or aurum.
There is really lot about this element so I will start with its chemical properties and where you can find it.

Attributes

Gold (Au) is amazing because it does not react much. It does not react with oxygen so you can easily have it in open place (while silver does react with oxygen), not only that but gold does not react with the strongest an-organic acids like hydrochloric acid (HCl) so only thing in which you can dissolve it is in aqua regia. 
On the left you can see aqua regia with piece of platinum which is very resistant too.

Once in Denmark during WW2 one chemist had two Nobel medals for some people. Those medals are made of gold and since Denmark was going to be captured by Nazis he did not want them to get those medals. He took them and placed them in aqua regia.
After the world he returned and the solution was still there so he extracted it and made new medals.

On the next picture you can see thin plate of gold. Gold is so ductile that one gram can be spread on 1 square meter. This picture is from Japan Toi museum.

This is very useful since gold is not very cheap but when you use only one gram for such a large area it gets to whole new level!

There is only one stable isotope of gold which is the one we are mining and using. There were found many others but all of them decay in matter of weeks, days or even couple of microseconds (actually some radioactive isotopes are used for curing cancer).

While gold does not react and so on, it is very soft so if you want to use it in jewelry it is always mixed up with palladium (white gold) or copper.

Gold is conductive. This is great but how does that happen?
Well gold and silver and copper are in the same column which means that they have similar properties. All of them are very conductive because they have one free valence electron.
So gold for example has configuration: 4f14, 5d10,6s1
“d” and “f” orbitals are both full since “d” has limit of 10 electrons and “f” 14.
You could ask why other elements with one valence electron are not so conductive and it is because the farther away from the core of the atom the easier it is to break the electron free. Also different atoms have different ionizing energy which means that it takes different amount of energy to free their electron.

Mining

Before I get to mining of gold I will mention the places where you can find it.

In the Earth’s crust there are about 0,0075-0,01 ppm of Palladium about which I wrote earlier. There is about 190 ppm of Vanadium but for gold it is: 0.0031 ppm. Which means that there is not much of it.

Unlike Palladium, gold was detected in the ocean to be 0.011 μg Au/l.
In whole Universe the estimated value of Au is one atom per 300 billions of hydrogen atoms, which is ten times less than palladium.

This is only guess but I think that this could be caused because in supernovas it is surely much easier to create element with 33 less protons.

Lets see how it looks like for different countries. The list of the countries is taken from Wikipedia and it is measured in tons (it is for mining in the year of 2013).

• 1.  China 420
• 2.  Australia 255
• 3. USA 227
• 4. Russia 220
• 5. Peru 150
• 6.  South Africa 145
• 7.  Canada 120
• 8. Mexico 100
• 9. Uzbekistan 93
• 10. Ghana 85

It is assumed that there were altogether mined 175,000 tons of gold. If you would pile it, it would use the volume of 21 cubic meters. While you may say that this is not much, imagine it standing next to your house + gold is very heavy. If you would make the same pile from hydrogen it would be about 200 times as large.

On the map below you can see the approximate storage of country’s gold (you could easily criticize it, look at South Africa.. but I did not find better, just don’t take it to be a good source).

There are few ways to mine gold. The older one, which you may have seen in movies and it is not used anymore, is the method of panning. This is based on the effect of gravity which pulls heavier gold down to the bottom of the bowl while the rest of the sand is slowly floating away (this was used often in rivers).

The modern way is to crush the material to small pieces and then leach it in some acid, rich in chlorine ions. It is then excluded in electric current on the cathode. There was also way to get it using mercury but only in specific situations and the soil was polluted with mercury.

Now there are ecological problems all the same because of hydrometalurgy which is the process of getting metals from their ores. There are huge amounts of cyanides used which in history already happened to cause some disasters, polluting large rivers and letting them toxic for years.

Usage

For the last chapter lets get to usage of this amazing metal.

In history the first usage was only jewelry. This is obvious since people back then did not even know what electricity is and they did not have enough gold to make isolation from it but it has such a nice color so they made lot of jewelry.

You can surely find lot of rings and various necklaces, this one is ring of Egyptian pharaoh. Like I said at the start, now gold is mixed with some other metal so it is not so soft.
You can see that metal gets different colors depending on the percentage of all the various metals.

Most often the objects are not whole made up of gold but rather only the top layer which can be extremely thin, even transparent.

Even in food you can find gold like a decoration, it is tagged as E175 and it is not dangerous at all since anything in human body is, won’t react with gold.

In industry, the property of high conductivity is used in computers in processors.

In dentistry gold is used as dental alloy, because again it does not react. There is not only gold but other metals too, mercury for example (because of Hg it is important for the alloy to not react and survive the environment in mouth).
I still remember when I went with my grandmother to guy who was collecting gold with her old golden dental alloys.

Gold was used as backup for money, this was called gold standard and I am going to write a whole separate post about it. This system fell and it is not used anymore.

Gold is even used by NASA. I read that for some flight there was 43 kg of gold used. To give specific example, there is gold used in astronauts helmet. This is because of radiation in space where you are not protected by atmosphere.
Gold foil will reflect most of the ultraviolet and infrared radiation which could otherwise cause serious damage to astronauts eyes. Full explanation.

This is all from me for today, already this has been the longest post ever so I hope someone will read it.

Dragallur

Cube of gold
Map of world gold storage
Other images from wiki articles about gold and gold mining and aqua regia

 

 

 

Elements of Periodic table: 2) Palladium

Hi,
this time comes the post about another element of periodic table. Last time it was Vanad and I will continue with Palladium!
Palladium is extremely important in car industry, it is also beautiful in jewelry and has surprising history.

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What I found most interesting about Palladium (Pd for the rest of the post) is that it is related to astronomy.
In the beginning of 19th century guy named William Hyde Wollaston was able to separate Pd and then he published it in a scientific journal. Some people thought that it was fake, that what he called Pd was just some kind of alloy of Nickel and Silver. Wollaston named it after dwarf planet found two months earlier called Pallas, you can see the planet on the right (Pallas is second largest dwarf planet in the belt between Mars and Jupiter).

Palladium is white and grey metal right above Platinum in the table of elements. There are many isotopes and lot of them naturally occur and few of them are radioactive decaying into Ruthenium, for example.

It is used on various things. In cars it is used as part of catalytic converter which is next to motor and takes CO and other toxic and poisonous molecules out. For the converter to be fully functional we had to stop using leaded petrol. (Wikipedia says that there are still companies in China that produce tetraethylead which is the source of the lead in petrol, it is making the car more efficient).
Pb (lead) was destroying these catalytic converters in very short time while now it is assumed that it should be working for over 120,000 km. On the left you can see the three way catalytic converter.

Palladium is used a lot in jewelry like “white gold”, also in dentistry because it is cheaper than gold, but some people may be allergic. Smartphones and lot of various electronic devices contain Pd.
Pd is also used as storage for hydrogen.

Now for mining. Most of Pd is mined in Russia,
South Africa is right behind then for a long time nothing and rest is produced by USA and Canada mostly.

Some sources say that Russia is running low with their storage, which would be big problem if true (it is the state secret so no one can be sure). In 2001 there was a Pd crisis when Russia had some problems with mining (the problem was linked to politics). Prices of Pd rose to over 1000$ per troy ounce (OZ=27 grams). It seemed that it would rise even more so Ford Motor Company bought a big amount and then the prices dropped rapidly, leaving Ford with loss about 1 billion $! On the picture below you can see the peak of the price and then the drop to about 200$. For now the price is about 560$/OZ for the last years the price seems to drop. On the next picture you can see the graph of prices for 18th December which of course do not change very much. In whole Earth there is about 0,0075-0,01 ppm (mg/kg) of Palladium. PPM is parts per million which is the same as miligram per kilogram. In sea water the amount is unmeasurable, because even the most precise technology is not able to detect it. In space there is about 1 atom of Pd per 30 billions of atoms of hydrogen.

Pd is also created in nuclear reactors but this source is not used.

Usually you will find pure (100%) palladium with gold or ruthenium around. Also oxygen is not reacting with Pd, which is extremely good attribute (this is not true above 800°C, then PdO is created on the top layers). For some time Pd was used as cure for tuberculosis but there were many side effects so it was banned. Pd is not very toxic since our body is not able to absorb it, but there is some evidence that it may be carcinogenic.

Dragallur

Pallas picture
Palladium picture
Catalytic converter
Palladium demand
Pie graph of production
Kitco 2001 graph
World map of Pd production

 

Elements of Periodic table: 1) Vanadium

Hi,
ok wow, yes it gets even more complicated when I create another series, lets see how it will work.
Anyway I will talk about Vanadium today. Have you ever wondered what is this element? How is it used? Where is it mined? What are its properties? Here we go, I will try to answer what I can.

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Vanadium (V for the rest of the post) is metal.
V has the atomic number 23 and it stands right next to Titanium and Chromium. So yes, V is pretty light metal and has lot of uses there.

V is mined mostly in China. Actually as you can see on the picture below the supply by china is

increasing in very high rate while other state`s production remains about the same. China is kind of able to move whole market with V.

V is mined not as clear metal but rather in some minerals like vanadinite or patronite. Also V can be found in fossil fuels but it is such a low amounts that it is not very usable.
For its usage.. as many other metals V is used in steel as ferrovanadium to increase the strange of steel. Then it can be used on various tools, for
the shell of nuclear reactor and with gallium like a tape for superconductive magnets. Also some very good batteries may be made with it.

For us humans, for survival Vanadium is not very useful but some fungi, algae and other organisms may contain it and also use it.

It is proved that lot of chemicals with V are toxic but with insufficient data one can only guess how much would kill him (or try it).

For consumption you can see that China has the largest demand. When they realized that vanadium can make steel twice as strong they become to use it in great mass (first boom was around 2004).

For various isotopes, the most common is V51 which is the one we are mining and also the only one which is not radioactive. The others have half-life mostly under couple of seconds with longest 330 days.

Dragallur

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4th picture