Role of isotopes in chemistry

[Sensei]

Hello!

 

Heavy water according to wikipedia is causing death of rats in a week of drinking.

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

 

The only difference from water is replacement of Hydrogen element by Deuterium, D2O or HDO.

Just because of extra neutrons properties such as boiling point, and melting point are slightly different (not to mention other hidden properties hard to measure).

 

D2O (Heavy water) Freezing point (°C) 3.82 Boiling point (°C) 101.4

HDO (Semiheavy water) Freezing point (°C) 0.0 Boiling point (°C) 100.7

H2O (Light water) Freezing point (°C) 0.0 Boiling point (°C) 100.0

 

This example shows that it's important to examine the all chemical substances with careful counting their neutrons as standard procedure.

Produce isotope pure element, then mix them with other isotope pure element, receiving mixture with well known neutron quantity, and use it instead in tests.

 

Hydrogen chloride acid can have more than 6 versions (4 stable):

H-Cl-35

H-Cl-37

D-Cl-35

D-Cl-37

T-Cl-35

T-Cl-37

Their properties should be slightly different.

Also result of their reactions with other substances should be slightly different.

Precise experiments should show how much.

 

Taking proper care of neutrons should open door for finding old-new materials, with different parameters (starting from different boiling, melting points).

f.e. plastics with Deuterium instead of Hydrogen in chains.

[mississippichem]

Well, kinetic and thermodynamic isotope effects are in general small. The most noticeable effect is when we exchange protium for deuterium as deuterium is essentially twice as heavy as protium. The small difference is easily observed by comparing sensitive enough IR spectra of HCl and DCl. This means that the energy of the bond changes when you switch isotopes.

 

Treating the vibration of a chemical bond as a quantum harmonic oscillator we find that the isotope effect for pairs of isotopes in other elements is much smaller as the reduced mass (a constant in the Schroedinger equation for the QHO) of the system changes relatively little with the addition of a neutron to a heavier element.

 

This also holds for more rigorous treatments of the chemical bond that don't use the reduced mass approximation.

 

Physical properties such as boiling point are affected but also to a small degree in most cases.

[Sensei]

Physical properties such as boiling point are affected but also to a small degree in most cases.

 

I posted it to inspire people to experiments. Everything should be created, checked and published.

For dead rats and small animals these things are not negligible and worth ignoring.

 

Replacing H by D, is just an example.

 

H2O has 18u

HDO has 19u (+5.5%)

D2O has 20u (+11%)

Some might say it's small change in mass.. (apparently not small for dead rats)

 

CH4 has 16u

CD4 has 20u (+25%)

Is it still small and not worth experiments showing what properties will have Methane with Deuterium?

 

C2H5OH has 46u

C2D5OD has 52u (+13%)

How other substances will behave after putting them to Deuterium Ethanol?

Will they be soluble (or not) at the same as with normal Ethanol? etc. kind of questions can be asked.

 

How will behave polyethylene/polypropylene which has only Deuterium? Will it bend or crack at the same moments as regular one?

 

Without creating these substances and careful examination how they behave we can't judge with 100% certainty how they behave.

Edited October 24, 2013 by Sensei

[John Cuthber]

Many of the materials you are talking about are available commercially. They are rather expensive compared to the ordinary H versions.

Apart from heavy water in the nuclear industry, I can't think of any applications of stable isotope substituted chemicals outside the laboratory, but that isn't because we don't know about them, it's because they are not very different from the ordinary versions and they are much more expensive.
http://www.sigmaaldrich.com/etc/medialib/docs/Aldrich/General_Information/bioms_brochure.Par.0001.File.tmp/bioms_brochure.pdf

Edited October 24, 2013 by John Cuthber

[Enthalpy]

Only hydrogen isotopes have different chemical properties, because the delocalization of the hydrogen nucleus is big enough to weaken the hydrogen bonds. Elements heavier and without hydrogen bonds differ chemically very little through the neutron count.

 

Few physical properties vary significantly through the isotopic composition. Superconductors depend a bit on isotopes, superfluid helium fundamentally. Diamond freed of ¹³C conducts heat many times better, silicon improves as well. Hydrogen used to passivate pending bonds at Si-SiO₂ interfaces is slowly knocked away by impinging electrons, and deuterium resists longer in this use. Deuterium is better for some gas-spark switches, lamps and some lasers. These significant effects rely all on the individual atoms' mass, not chemical affinity.

[swansont]

Diffusion is affected by the different masses, and there are processes that use radioactive isotopes of an element as markers.

[mississippichem]

There is also the little known trick of breaking a carbon-tritium bond by the tritium beta decaying to helium. It's a neat way to make spin doublet carbon atoms, though not very practical.

[John Cuthber]

"Only hydrogen isotopes have different chemical properties,"

Not quite true

http://www.tandfonline.com/doi/abs/10.1080/01496398808057664#.Umlk__n_kao

 

 

But the differences are usually only laboratory curiosities, rather than practically useful.

[Enthalpy]

"Only hydrogen isotopes have different chemical properties,"

Not quite true

http://www.tandfonline.com/doi/abs/10.1080/01496398808057664#.Umlk__n_kao

Thank you!

And lithium belongs to the elements interesting to separate into isotopes, so a simple method is useful.

[daphne2013]

It can be used as tracking atoms such as tap water, water pipes broke, isotope in Cl can be used for tracking, then can detect the break place, there are some reaction mechanism is also had the same isotopic effect to explain.