Why does mercury in mercuric acetate have a lone pair?

The configuration of mercury ends with $6s^{2}$. In mercuric acetate, mercury is in the +2 oxidation state, so does it still have a lone pair?

• Of course it has lone pairs. 1s², 2s², … – Jan Sep 30 '16 at 22:03

2 Answers

TLDR:

Mercury in its (+2) salts does not have lone pairs readily accessible for covalent bonding. However, its 5d electrons do affect its properties, resulting in a relatively high polarisability.

The long story:

Mercury is the last 5d element and has electron configuration $[\ce{Xe}] 4f^{14} 5d^{10} 6s^2$. The $6s$ electrons are the outermost electrons and readily available for covalent bonding. $4f$ electrons are virtually inert since they are very deep. $5d$ electrons belong to the previous shell, but are the outermost of them and once mercury looses its $4s$ electrons, $5d$ electrons become the outermost and define its properties. They are still too strongly bound to the nucleus to participate in covalent bonds under ordinary conditions ($\ce{HgF4}$ was only observed spectroscopically in inert gas matrix). , but are far enough to wiggle around and participate in non-covalent interactions, such as van-der-waals interactions. $6p$ orbitals are also available for covalent bonding, though extent of their use is often debatable and/or unobvious.

These are 5d electrons. They can participate in chemical bonds, e.g. in mercurinium cations.

• You should elaborate. – Mithoron Feb 7 '16 at 21:49