Why does mercury form weak metallic bonds?

1 Answer

Because of the closed electron configuration of #"Hg"#.

Explanation:

The electron configuration of mercury is: #"Hg: [Xe] 4f"^14 "5d"^10 "6s"^2#.

All subshells are filled, so a #"Hg"# atom is less likely to ionize than other transition metal atoms.

Therefore, there are few free electrons in mercury, and weak metallic bonds are formed.

See also:
http://antoine.frostburg.edu/chem/senese/101/periodic/faq/why-is-mercury-liquid.shtml