Mercury's most famous property is that it is the only metal that is a liquid under standard conditions. Why is this?
An exceptionally low boiling and melting point for a heavy d-block element has always been explained by relativity but no hard evidence has been found to back this theory up. Until now!
Quantum mechanics were used by a team in New Zealand to calculate the heat capacity of mercury with and without considering relativity. The result of these calculations showed that when considering relativity, the melting point matched almost exactly on the experimental value of -39 degrees Celsius.
Now you may ask, what exactly is relativity?
The theory of relativity, by Albert Einstein, considers that in atoms, the velocity of the innermost electron is related to the nuclear charge. As nuclear charge increases, the atoms must move faster in order to prevent the innermost electrons from 'falling' into it. Going down the periodic table, this theory is shown as the electrons within the 1s orbital move faster and faster meaning that the element becomes heavier and the atomic radius decreases. This effect can stabilise orbitals or destabilise them (again by the theory of relativity).
In the case of mercury, bonds are not formed between surrounding atoms, the outer electrons stay within their orbital and do not become associated with other mercury atoms, forming weaker van der Waals bonds and therefore giving mercury a lower melting point than we would expect.
No comments:
Post a Comment