[Coeus]

I was wondering why is gold soft when metallic bonding is supposed to get stronger when the atoms are able to distribute more electrons?

Edit: Nevermind, if anyone was wondering this site explained it very well (it's also the only site that explained it at all that I could find)

https://khabibkhumaini.wordpress.com/2009/02/05/relativity-phenomenon-why-is-mercury-liquid-and-gold-soft/

[Enthalpy]

You can forget the linked explanation. First, the author hasn't understood the screening effect nor several more, he didn't check other elements for obvious counter-examples, and second, hardness is not an atomic property, since it fully depends on alloying.

(Many!) Other authors would like to relate hardness with the crystal structure, but this doesn't work at all. The appended table shows there is no relationship.

Ductility relates fully with the ease of propagation of dislocations, which has very little relation with simple chemical properties of the atoms. For instance, just 0.05% of H or N make steel harder and more brittle, and so does 0.2% C. Even less O acts on Be or Ti.

[Enthalpy]

The appended table was missing, I try to append it here.