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.


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.


 

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

 

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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 -_-.


What happened this day was very suprising to me, it was this reaction below:Autoprotolyse eau.svg

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

 

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?


 

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