Category: Chemistry


In school we are taught that there are two different kinds of chemical bonds that atoms can make; ionic bonds, where electrons from one atom are donated to another atoms, and covalent bonds, where electrons are shared between two atoms. The truth is that real chemical bonds are a mixture of both. When two atoms come together their atomic orbitals in the sub shells combine to form molecular orbitals. For every two atomic orbitals that collide, two molecular orbitals are created, one in a lower energy state than the other.

The lower energy state orbital is lower than either of the two original atomic orbitals and is known as the bonding orbital, by comparison the other molecular orbital is in a higher energy state than either of the atomic orbitals and is called the anti-bonding orbital. Where both orbitals have the same number of electrons in it, the difference between the anti-bonding orbital and the highest energy atomic orbital is greater than the difference between the bonding orbital and the lowest energy atomic orbital and so the bond wouldn’t form as both molecular orbitals would be in a higher energy state than the atomic orbitals from which it is formed. This is why atoms with full outer orbitals (the noble gases) don’t like to form molecular bonds here on earth. Maybe a diagram is in order:

The point of all this is that scientists in Norway have used computer simulations to model chemical bonds in the extreme magnetic fields of neutron stars and white dwarfs. They have found that a new type of chemical bond is formed at these extreme magnetic fields. The basis is that in these magnetic fields, the anti-bonding orbital can exist at a lower energy state than the highest energy atomic orbital. This means that the noble gases will be able to form new and interesting molecules of which the likes have never been seen on earth before. The only catch, and it’s a big one, is that the magnetic fields need to be in the region of 105 T which in much, much, much bigger than the measly 30-40T fields that we can muster here on earth at the minute. Ah well.

 

T. Gloess

Chemical Olympics

I get bored easily. Very easily. Since the Olympics are beginning soon I decided to put together a list of world champion substances and materials; unfortunately we only award gold here. Times-a-wasting, so here we go!

Most acidic:

The chemical structure of fluoroantimonic acid.

Our first winner is fluoroantimonic acid (HSbF6). This superacid is 20 quintillion times stronger than 100% sulfuric acid. It is formed by the exothermic reaction of hydrogen fluoride (HF) and antimony pentafluoride (SbF5); although effectively ‘naked’ the proton is always attached to a fluorine atom by a very weak dative bond which is why it is so acidic.

Most basic (alkali):

A superbase has a very high affinity for protons and is easily destroyed by water, oxygen and carbon dioxide due to deprotonation. So I will say that the winner here is the hydroxide ion (OH). However although it is the strongest base possible in aqueous solutions, stronger bases exist, just not in water.

Most corrosive:

Coming in as joint winners Argon or Oxygen plasma are the most corrosive substances in the world. They can be made to oxidize just about anything down to its simplest molecular oxide whether it be glass, metal or a polymer, it makes no difference. The plasma is made in-situ by streams of argon and oxygen that are heated by a radio frequency power supply. The atoms of gas can be heated to insanely high temperatures and values as high as 100,000,000 Kelvin have been reported. Want something corroded? Just throw it in, it will disappear quickly enough.

Densest:

Osmium. Nothing more. Nothing Less.

Osmium wins as the densest naturally occurring substance at standard temperature and pressure at 22.59g/cm3. It wins by 0.03g/cm3 just pipping Iridium to the title.

Hardest:

Diamond? Not any more, as lonsdaleite (also known as hexagonal diamond), a carbon allotrope, wins as the hardest substance. It forms naturally when graphite-containing meteorites strike the earth. The immense heat and stress of the impact transforms the graphite into diamond, but retains graphite’s hexagonal crystal lattice. A pure simulated sample was found to be 58% times harder than diamond.

Strongest (tensile):

Walls of carbon nanotubes.

The winner here is (multiwalled) carbon nanotubes, yet another carbon allotrope, this time with a cylindrical structure. It has the highest tensile strength of any material yet measured, with labs producing them at a tensile strength of 63 GPa (yet this is still well below their theoretical limit of 300 GPa).

Highest Young’s modulus:

Finish(ing first). The Diamond standard.

It was bound to win something; diamond is the substance with the highest (measured) Young’s modulus. The world’s most famous carbon allotrope has a gleaming Young’s modulus of 1220 GPa (pun intended).

Toughest:

(Titanium-based) Metallic glass. Looks just like metal.

Metallic glass, created by scientists in California, is found to be the toughest material on the planet, beating steel. The glass is microalloy made of palladium that has a chemical structure that counteracts the inherent brittleness of glass, but maintains its strength. It’s not very dense and it is more lightweight than steel, with comparable heft to an aluminium or titanium alloy.

Most electronegative:

As every educated chemist should know, fluorine wins as the most electronegative element with an electronegativity of 4.0.

Most electropositive:

Francium in water = Bad, bad idea

Francium wins as the most electropositive element. It is at the bottom of its group on the Periodic table and it loses electrons very easily.

Highest melting point:

Tantalum hafnium carbide (Ta4HfC5) is the substance with the highest melting point at 4488 Kelvin. This beats carbon which only has a melting point of 4427 Kelvin.

Highest boiling point:

Here I am going with joint winners. Either Tantalum carbide (TaC) or Tungsten wins, as they both have boiling points that range between 5770-5950 Kelvin.

Most flammable:

Burns through sand. Nuff said.

Chlorine trifluoride (ClF3) explodes as the most flammable substance on the planet (the puns just keep coming). An extremely powerful oxidizing agent, chlorine trifluoride is extremely reactive with most inorganic and organic materials, even plastics, and will initiate the combustion of many materials without a source of ignition. If that’s not scary enough, in an industrial accident, a spill of 900 kg of chlorine trifluoride burned through 30 cm of concrete and 90 cm of gravel beneath it.

Most radioactive:

Gulp !

Polonium-210, I would say, wins as the most radioactive substance on the planet. It is so radioactive that it glows blue because the air around it becomes excited by the radiation it releases.

Most toxic:

Mr Plastic, in the flesh.

The winner here is the botulinum toxin (C6760H10447N1743O2010S32), produced by the bacteria Clostridium botulinum and used in Botox, is the most toxic substance on the planet. In fact, an amount equal to a grain of salt would be enough to kill a 200 Ib man.

Fastest (natural) acceleration:

Try to blink and you’ll miss it.

It is really chemistry but the Pilobolus fungi can accelerate its spores at roughly 20,000 G; that’s equivalent to 33,381ms-2 at sea level or launching a human through the air at 100 times mach speed. Now that’s fast!

Although I deviated a little from chemistry near the end, I hope you enjoyed reading about these world champion substances and materials. If you disagree with any of them or think I should include another category feel free to comment.

Sources:

http://en.wikipedia.org/wiki/Orders_of_magnitude_(density)

http://en.wikipedia.org/wiki/Lonsdaleite

http://en.wikipedia.org/wiki/Fluoroantimonic_acid

http://en.wikipedia.org/wiki/Superbase

http://chemistryiit.blogspot.co.uk/2008/11/super-acids-and-super-base-concepts.html

http://en.wikipedia.org/wiki/Ultimate_tensile_strength

http://www.popsci.com/technology/article/2011-01/new-metallic-glass-toughest-strongest-material-yet

http://en.wikipedia.org/wiki/Young’s_modulus

http://answers.yahoo.com/question/index?qid=20070712141046AApzEj2

http://en.wikipedia.org/wiki/Chlorine_trifluoride

http://web.archive.org/web/20060318221608/http://www.airproducts.com/nr/rdonlyres/8479ed55-2170-4651-a3d4-223b2957a9f3/0/safetygram39.pdf

By Myles Scott – The Demotivator

Bear with me on this article as it is my first and my thought pattern does jump around a lot when I am trying to explain stuff i.e. you may be confused with the way I explain stuff. And yes I know this is long.

The most useful tool that any chemist, in fact any scientist, can utilise is the periodic table of elements. A list of 118 elements (four of which are not verified) that everything that exists is made out of; ever; in the whole history of everything. My friends this is the answer to life, the universe and everything. But what is it and why is it in this particular arrangement. The first 92 elements from Hydrogen to Uranium are naturally occurring. Of those 92, the first 26 are made in the centre of stars via nuclear fusion (I may do a quick article on this in the near future). Elements 27 to 92 are created when stars explode in a supernova where temperatures can reach hundreds of millions of degrees. The rest, from 93 onwards, have been made in labs around the world; you may be able to tell where by element names.

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Going back to key stage 3 and GCSE there are several main areas to the table. There are metallic and the non-metallic elements. The metals are the left of the zigzag line, in the green and turquoise area, and the non-metals to the right. There that’s key stage 3 chemistry.

These can be further broken down. The orange column (group 1) are called the alkali metals, the yellow (group 2) are the alkali earth metals. The block of elements in the middle is known as the transition metals. Elements in turquoise are poor metals and the green elements are non-metals. The blue column to the right (group 8 or 0) is known as the halogens. Group 7 also has a special name, they are referred to as the halogens. Elements in each group have different properties, reactivities and generally cool stuff about them but if I were to go into all of that I would be here for way too long.

The man we owe the most for creating this table is Russian all-time great lad Dmitri Mendeleev. This man was responsible for making the most important leap in addressing the categorisation of the elements. Mendeleev left blanks, spaces which he thought yet to be discovered elements would fit into. It had been known for a few years that each element had a different weight, something we owe to Jöns Jacob Berzelius. Mendeleev utilised this and also the fact that many elements have similar properties to create his magnificent table. Up until that point many scientists used either one or the other to order the elements. Mendeleev used both and whilst his first table wasn’t perfect it was pretty darn good.

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This was THE major step towards what we now think as the periodic table of elements.

But enough of how it was made, what makes it so wonderful.

Within the table there are many different patterns to see. The table is made up of 7 rows or ‘periods’ that show the number of electron shells around the nucleus and 18 columns or ‘groups’ that show the number of electrons it is outer most shell. For example Carbon is in period 2, group 4 so has two shells of electrons and four electrons in its outer most shell. Each electron shell can only hold a certain number of electrons. The first shell can hold only two, the next eight the, third is also eight however the fourth and fifth can hold 18 each and the sixth and seventh 32. Taking carbon again as our example, it has two electrons in the first shell but this is then full and so it moves to the next shell where it happily fits the other six electrons in.

The next fantastic thing about the modern periodic table is that these electron shells are then further divided into sub-shells. There are four sub shells S,P,D and F. like the electron shells these can only take a certain number of electrons. The S sub-shell can take two. The P shell six, the D shell can take another 10 before it is full and the F can take 14. These also fill up sequentially, so to drag carbon away from whatever it was doing again and take it as an example again. The first shell in a carbon atom can take two electrons as we have already seen and so it only needs the S sub shell before it is happy. The next shell up can take another eight so we need the S sub shell with two but that leaves us six electrons short, perfect for the P sub-shell and now the 2nd electron shell is happy. The third again needs S and P before it is full but the fourth electron shell needs to use up the D sub shell as well as the S and P. This continues on up to the sixth and seventh needing the F subshell as well. This has been a bit of a tangent but we are getting to the relevance to the table now. There are four main areas of the Periodic table. Groups 1 and 2 are called the S-block. The part between groups 3 and 8 is called the P-block, the transition metals are referred to as the D-block and the Lanthanides and Actinides are termed the F-block. This term relates to which sub-shell the outer electrons are situated in. In the S block the outer electrons are in the S sub-shell and so on. This further explains the reactivity of the groups.

This concludes my whistle stop tour of how the periodic table is structured, if you want to see how many you can name then please take this test: http://www.sporcle.com/games/g/elements. Come and find me if you think you have beaten my best!!!

T. Gloess