Mercury (Hg). Diagram of the nuclear composition,electron configuration,chemical data,and valence orbitals of an atom of mercury-201 (atomic number: 80),an isotope of this element. The nucleus consists of 80 protons (red) and 121 neutrons (orange). 80 electrons (white) successively occupy available electron shells (rings). Mercury is a transition metal in group 12,period 6,and the d-block of the periodic table. It is the only metal to be liquid at room temperature,freezing at minus 39 degrees Celsius. This is because the d-subshell shielding effect of outer (valence) electrons ends. It is a toxic metal,used in thermometers,barometers and manometers |