Posted by: Mark Foreman | February 13, 2010

The likely origin of the steric repulsion (The correct view of the atom)

Some years ago I was sitting in my office in england with a man from the Iranian national nuclear research centre and we were looking at drawings of atoms.

As both of use were men who are experenced in “the ways of the atom” we started to share a joke. We looked at a series of symbols of companies and other organisations, the key feature we were looking at was the relative size of the atom and the nucleus.

We held the view that the right way to draw the atom is to not show the nucleus as if the drawing shows the electrons then on the same scale it is impossible to see the nucleus.

I have repeated the game that me and my late friend played, and to my shock the IAEA have drawn an atom which might fail our test. It has a dot which might be an electron or it might be the nucleus. (http://www.iaea.org/). I checked an old copy of the IAEA site and the nucleus is even more easy to see (http://web.archive.org/web/20000815073124/www.iaea.org/worldatom/)

Atomic Energy of Canada (they make CANDU nuclear power plants and other nuclear equipment) did better. They do not use an atom as their current logo, but the first atom which I found on their site was drawn correctly. (http://www.aecl.ca/site3.aspx look for “Update on Licensing Activitieson this page)

The Royal Society of Chemistry (www.rsc.org) have an atom which looks wrong. I think that I can see a nucleus at http://www.rsc.org/AboutUs/ChemistryCentre/index.asp.

The American Chemical Society (ACS) did not have an atom on their front page, so I will not test them.

Many of the atoms in yahoo images got it wrong

The one which vexed me most was at http://www.standards.dfes.gov.uk/specialistschools/pdf/SCI_GD.pdf?version=1 where the UK government organisation in charge of schools got it wrong.

Now you might ask why do I find this game interesting, the reason is that if you know about the H. Geiger and E. Marsden (gold leaf) experiment done under the supervision of Rutherford at Manchester in 1909. Then you will know that the positive charge in an atom is concentrated in a very small space at the centre of the atom.

So I hold the view that the steric effects are due to the electrostatic repulsion between the electrons in different atoms. This will explain that even while the floor is mostly empty space the electrostatic effects stop us falling through the floor towards the centre of the earth.

The chemistry which we see is due to the electrons which are part of the atoms. We can see evidence for the tiny nucleus but there is little that we can do to the nucleus.

I know that two things can be done with chemistry to the nucleus. But compared with what I can do to the electrons in the outermost shell these things are close to nothing.

1. We can alter the magnetic field which it experiences, this is an important effect in NMR spectroscopy.

2. For one type of beta decay (electron capture) we can slightly alter the rate by changing the chemical environment of the atom. I think that the decay constant (which gives the half life) of a proton rich isotope of beryllium has a slight chemical dependency. In aqueous solution it is slightly different to the value in some solids.

Please do not worry about the decay of isotopes such as Be-7, it is a super advanced topic which is very unlikely to ever be on an exam. For almost all radioisotopes the decay rate is fixed and can not be changed by any chemical or physical means.

If you want to read about the radiochemistry of this ‘fun isotope’ then read J.J. Kraushaar, E.D. Wilson and K.T. Bainbridge, Physical Review, 1953, volume 90, page 610.

WARNING. Do not try any experiments with radioactivity unless you either are an expert in radiological matters or are working under the supervision of someone who is. So do not try any radiochemical experiments in your basement/kitchen/garden shed. Also beryllium is a very nasty element, if it was a person I would view it as being “pure evil”. Chemicals have no morals, only people can have morals thus chemicals can not be good or evil. I think that some forms of beryllium are more toxic than plutonium-239. Beryllium is at the top of my rather short “dirty washing list” of chemicals which I refuse to work with.

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