Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: ordinarypeople on 21/09/2010 18:23:51
-
Of the pentachlorides, PCl5 and SbCl5 are stable whereas AsCl5 is very unstable. Why is that?
-
[???] I don't know. I wonder what BiCl5 is like?
-
I wonder what the crystallography of these compounts is like. It might matter.
-
It seems that it has to do with the amount of electrons on the molecule's outer levels. The Cl and As create covalent bonds because the As is unstable with only 5 electrons on its outer level. The Cl has 7 electrons on its outside energy level. Once they bond, the Cl is stable with 8 electrons on its third energy level, and As still needs one more electron to be stable. Unless it takes an electron from another element with an extra electron, it will be unstable with its 5 electrons, and therefore, it makes an unstable molecule.
But, don't take my word on that..someone back me up/correct me? [:I]
Scratch that, PCl5 has 5 electrons on its outer level also. Could it be because As is poisonous? [???]
-
Of the pentachlorides, PCl5 and SbCl5 are stable whereas AsCl5 is very unstable. Why is that?
http://en.wikipedia.org/wiki/Arsenic_pentachloride
The pentachlorides of the elements above and below arsenic in group 15, phosphorus pentachloride and antimony pentachloride are much more stable and the instability of AsCl5 appears anomalous. The cause is believed to be due to incomplete shielding of the nucleus in the elements following the first transition series (i.e. gallium, germanium, arsenic, selenium and bromine) which leads to stabilisation of their 4s electrons making them less available for bonding. This effect has been termed d-block contraction and is similar to the f-block contraction normally termed the lanthanide contraction.