Mercury

The principal characteristics of mercury:

Name:Mercury
Symbol: Hg
Atomic number: 80
Atomic weight: 200.59 (2)
Standard state: liquid at 298 K (the heaviest known elemental liquid)
CAS Registry ID: 7439-97-6
Group in periodic table: 12
Group name: (none)
Period in periodic table: 6
Block in periodic table: d-block
Colour: silvery white
Classification: Metallic

Mercury is a chemical element. It's symbol is Hg, because in greek means "hydr-" water and "argyros" silver (or mostly known as quicksilver).The atomic number of this element is 80.
it's a heavy, silvery d-block element.

Mercury is not usually found in nature so it occurs in deposits throughout cinnabar, mostly found in Spain and Italy.
This is the only element liquid at normal temperatures.
It's so poisonous because it density is 13.5/cm3, so when you ingest it, your blood gets densest and your body can't support it and your organs started to fail.
As compared to other metals, it is a poor conductor of heat, but a fair conductor of electricity,Mercury does not react with most acids

Mercury is used in:
Thermometers and traditional blood pressure monitors.
In dentistry amalgam fillings are used for repairing cavities. These contain 50% mercury.