Period 6 element deposited later by meteorites which contained the element. This supposedly explains why, in prehistory, gold appeared as nuggets on the earth's surface. Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum ( < Greek "" "water" and "" "silver"). A heavy, silvery d-block element, mercury is the only metal that is liquid at standard conditions for temperature and pressure; the only other element that is liquid under these conditions is bromine, though metals such as caesium, francium, gallium, and rubidium melt just above room temperature. With a freezing
Period 5 element number increases in the alkali metals, for it is more reactive than potassium, but less so than caesium. In addition, both potassium and rubidium yield almost the same hue when ignited, so researchers must use different methods to differentiate between these two 1st group elements. Rubidium is very susceptible to oxidation in air, similar to most of the other alkali metals, so it readily transforms into rubidium oxide, a yellow solid with the chemical formula RbO. Strontium is the second element placed in the 5th period. It is an alkaline earth metal, a relatively reactive group, although not nearly as