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

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

Why is HClO4 stronger than HClO?

Hi,
so this monday we had chemistry class again and because we are learning about halogens our teacher mentioned some acids and she explained why some of them are stronger than other. She got to the point of comparing HClO4, HClO3, HClO2 and HClO. She arranged them in this order in decreasing acidicity explaining why. As I found out over time, she is oversimplifying things, in this post I will try to show why they are in this order.

Almost like water, the picture of perchloric acid. (HClO4)

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So here we have four acids (to make it faster I will compare only first and last one). Both are same except that there are three more oxygens in HClO4 and the oxidation number of Cl is VII on the left and I on the right. Now this has to be the reason for different properties.

In all of those molecules Cl is the middle one, which means that all oxygens are connected to it with double bond, except one with only simple one which has hydrogen on the other side.

The picture shows the structure of these molecules.

So as you probably know water has what is called “dipole moment”. This is a term that is used for molecules that have partiall charge on one side and the other charge on the other side.

This has very interesting properties but what is important is that HClO4 has this too, and much more than HClO because there are oxygen ions which have charge of -II making chlorine in the middle of them a lot “ripped off” because there are those oxygens with higher electronegativity that are trying to get those electrons to get on the configuration of noble gases.

Now before the conclusion we must clear out the definition of acidic molecule. Such a molecule is acid when it is good at giving H+, so now the question is, why is HClO4 better in giving H+ than HClO?

So the key lies in what happens when these acids break up. When HClO4 becomes ClO4- there is not so much stress into getting the hydrogen back because delocalized electrons from the other oxygens [1] can ease it up making the molecule more stable while in HClO loses only one of two donors of oxygen making the molecule want it back a LOT.

Simply:

Electron withdrawal increases strength.

If you are not sure about this, ask me in the comments or check out the resources that I used.

Dragallur

Resources: 1|2|3|4|5|6

[1] Yes oxygens here have all two free electron pairs which are doing some wonders!

 

 

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

 

 

Chemical bonds, part 2

Hi,
it has been more than month since I wrote about chemical bonds. It was easy post just an explanation to all kinds of bonds: covalent, coordinate, ionic, two days back I updated it so there are even polar and nonpolar bonds but what I want to look on right now are sigma, pi and whole other kinds of bonds. This is a different perspective, it is more kind of from inside. Again like few other chemistry posts I made this because our teacher in school as I found out did not learn us what I would say is interesting and maybe important.

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So from the last post we know that atoms that are bonded together are bonded in different ways, usually this is just dependent on the electronegativity, or if it is metal or not. But then you can look in these bonds and sort them in other groups:

σ bond

σ is a sigma bond. This is the most basic kind. Bonds create when there is enough energy and the atoms are turned toward each other in right way. Always when there is bond, double or triple there will always be one sigma bond and it will be the first bond to create. This bond is also the strongest one. Sigma can form between s orbitals or two p orbitals or s and p or even two d’s. There are some more conditions about axis and so on but if you have a single bond between two atoms it always going to be sigma.

π bond

π is a pi bond. This is the second most common one and you can have more of them between two atoms. For example triple bond will be usually made up of one sigma and two pi bonds. They are not so strong, when you know this you know that when you will break them up, pi bonds will be the first ones destroyed. 

Because pi bond looks like the one above, the orbitals do not overlap so much, the force is not so strong. Second picture shows where is probability cloud strongest. The combination of sigma and pi bond is actually very efficient since it contracts the length of the bond making it stronger.

δ bond

δ is a delta bond. Actually I have never heard about this one before, but it is the bond that first appears when you have quadruple bond. This is very rare but some atoms can have even quintuple bonds between each other. When there is such a quadruple bond there is also one sigma bond and two pi bonds with delta bond. It creates by overlaping of two d orbitals, that is why it is called delta bond. Metals as rhenium, molybdenum or chromium can have such a bond.

On left you can see how this overlap should look like, this particular one is for two molybden atoms. But I can not really imagine how those look like really..

 

φ bond

φ is a phy bond. This last one is kind of only for fun since we were able to observe it only between two uranium atoms because they need two f orbitals which are found only in really heavy elements which are usually either radioactive or made only by human and usually both.

On the right you can see two f orbitals that could touch each other and maybe create this crazy bond.

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So how is this related to covalent bonds and so on again? You can sort bonds between atoms into groups. For example bond between two carbon atoms will always be covalent bond because there is 0 difference in their electronegativity. It does not matter if there are two or three bonds inside. Then you can look on them and sort them if they are sigma, pi or even delta bonds which depends on their orbitals.

Dragallur

 

Is water extremely poisonous?

Hi,
the title could be misleading but that is actually what I will write about. What happened to me this week in the school was pretty interesting. We were in chemistry class and it was nothing too unusual. Then at one point the teacher said something what sounded to me very illogical, this would not be for the first time, last time the teacher said that plasma has to do a lot with absolute zero -_-.

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What happened this day was very suprising to me, it was this reaction below:

Two molecules of water will change into hydroxide and hydronium. This process will go back because of chemical equlibrium.

Why? When I saw this on the chalkboard I thought that this is some kind of crap, but actually it is very interesting. At first I thought that she just forgot to write some kind of catalyzator but no, this is equation.. it seemed to me that she wants me to believe that water just alone changes to base and acid.

Now this actually really happens. The problem is that the concetration of such ions is

1.00×10⁻⁷ mol∙dm⁻³

This is not much since one mol is the number of carbon-12 atoms in 12 grams while this is much more space in decimeter and there is not many moles in there (10⁻⁷).

How this happens? Well you may ask, why should water do this? Is it not stable? Well this is because of random fluctuations inside the molecules which may cause such thing. For every ten hours this happens approximitely once per molecule of water. The process takes only few femto seconds which is quite cool and after sometime I guess that it will just return while other molecules will do this again (because there are both acidic and basic ions they will cancel out so water is neutral).

This is important since this is why water is conductive, because there are ions even in pure water. This process is called self-ionization or autoprotolysis.

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.

Chemical bonds

Hi,
this post is just a systematic list and explanation of chemical bonds because I needed to learn them for chemistry class and at the same time, why not make a post from it?

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Chemical bonds are bonds between two atoms. There are various ways in which they can “connect”, and that is what this post is about:

Covalent bond

Covalent bond is bond between two atoms which causes sharing of electron pairs. The difference between electronegativity is less than 1.67. If it would be bigger than the bond would be called ionic bond. Covalent bond is always going to be between two same atoms, for example H-H or   C-C and so on.

EDIT (18.2.2016): Also if the difference is less than 0.4 the bond is nonpolar while if it is between 0.4 and 1.67 it is polar bond. This is important when you want to dissolve some stuff because only polar things with polar dissolve and nonpolar and nonpolar while not polar and nonpolar. For example water has polar covalent bond because the difference is roughly 1.2 or so.

Ionic bond

Ionic bond is extreme case of covalent bond since the difference between electronegativity of two atoms is greater than 1.67. This means that one atom is going to attract the other electron so much that the first atom wont even hold it anymore. Examples of such cases are: Na+ and Cl– or Li+ and F– .. this “plus” means that the electron was moved a lot towards the other atom while “minus” means that the atom has a lot greater electronegativity and is able to catch this electron causing the atom to be negatively charged.

Above you can see how atom of fluorine takes one electron from lithium under his control (red arrow). Such molecules are easily dissolved in water and they are called non-polar molecules.

Dipolar bond

Dipolar bond is very similar to covalent bond and it can create when one of the atoms do not have any free electrons while the other one has two in one orbital. One of them then may move to the first atom and create bond with the other electron which is alone now.

Because bond can always create from electrons of opposite spin, with dipolar bond you can be sure that it will create because both the electrons came from one orbital so they have to have opposite spin.

An example of such a bond is NH4. Nitrogen has three orbitals ready to be connected with hydrogen which happens. Then the last hydrogen is actually H+ so he does not have any electron but nitrogen can share both his electrons from 2s2 orbital as you can see on the next picture. Here nitrogen is called “donor” and hydrogen “acceptor“.

Metallic bond

Metallic bond is very often seen on metals and it is the reason for their thermal and electric conductivity. As you can see below atoms are all positively charged, which means they are cations while their electrons keep flying around making what is called “electron gas” (as you can see on the next picture), that is why the current so easily “flows” through metals.

Dragallur

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

 

1) Particles: Prologue

Hi guys!
I am back with probably short post because I am lazy and tired these days. I know I wanted to start something about triangles but right now I am not that excited for it so I will make some posts about particles. I talked about some before but I have never explained what the hell are quarks for example.

So first of all… particles. Well we think about them like small stuff that is everywhere and everything is made up of it. That is right.
So I will start with molecules, easy peasy those are just two or more atoms made up together.
Atoms are (small), there is some stuff in them but first of all there are “kinds” of atoms, substances and that is Hydrogen, Helium, Oxygen, Carbon. They are made up all from the same things but with different amounts. Atoms are made up of core and shell. Usually, you wont do anything with core. It is very stable and not interacting. In our organism there are only changes in molecules. That means that some atoms will move somewhere else and that will change molecules properties.
Shell is made up of electrons. Electrons are NOT made up of something else, it is just primal stuff. Electron belongs to group of particles that are called elementary particles. It´s sub-group is called fermions and its sub-sub-group is leptons which are really small and light.
Core is made up of neutrons and protons. As I talked about them in four fundamental forces series those are particles (sub-atomic) that are hold together by strong force. Anyway protons are positive and neutrons neutral.
There is huge experiment going on in Japanese which is trying to proof that protons are decaying. Its problem is that one proton has half time about 10^31 years long. They did nice trick so they do not need to wait so long by monitoring ultra clear water. There are thousands tons of water and their machines are able to detect any proton decaying to photons.
Photons are also elemental particles but their sub-group is special for particles that are carriers for fundamental force: photon, gluon, bosons but not graviton because he is only hypothetical. Photons are massless which is why they can travel at the speed of light.
At last for review there are quarks which are elemental particles, even fermions like electrons but they are in special group for quarks.
I actually read something about quarks not being elemental (only hypothetical). It was said that if they are not elemental we can not be sure that there is unlimited number of smaller and smaller particles.

This was just a short preview of what I will write about next time.
Dragallur