Michael R. Topp, professor of chemistry at the University of Pennsylvania, explains.
Although some of the symbols on the periodic table may seem strange, they all make sense with a little background information. For example, the symbol for the element mercury, Hg, comes from the Latin word hydrargyrum, meaning "liquid silver," a more recent version of which was the English "quicksilver." Many other elements that were known to the ancients also have names derived from Latin. The table below lists some examples for which the initials do not correspond with their modern English names.
The rare (or inert) gases were discovered much more recently and tend to have classical-sounding names based on Greek. For example, xenon means "the stranger" in Greek and argon means "inert." Helium is named after the sun.
So far, 110 elements have been formally named. Newly discovered ones have names determined jointly by the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP), which gives discoverers the chance to name them. All of these "new" elements are synthetic and the discovery of each needs confirmation. An abstract published by IUPAC gives insights into the procedure: "A joint IUPAC-IUPAP Working Party confirmed the discovery of the element with atomic number 110. In accord with IUPAC procedures, the discoverers proposed a name and symbol for the element. The Inorganic Chemistry Division recommended this proposal for acceptance, and it was adopted by the IUPAC Council at Ottawa, 16 August 2003. The recommended name is darmstadtium with symbol Ds."
The proposal to name element 111 Roentgenium, symbol Rg, has been recommended for approval by the Inorganic Chemistry Division Committee of IUPAC. As they state: "This proposal lies within the long-established tradition of naming elements to honor famous scientists. Wilhelm Conrad Roentgen discovered x-rays in 1895."
For informational purposes, as yet undiscovered elements having higher atomic numbers are assigned so-called placeholder names, which are simply Latinized versions of their atomic numbers. Thus element 111 was formerly designated unununium, literally "one one one," (symbol "Uuu") and element 112, which is still formally unnamed, has been given the temporary name of ununbium (symbol "Uub").
[Editor's note: The name roentgenium for the element of atomic number 111 (with symbol Rg) was officially approved as of November 1, 2004.]