|MadSci Network: Science History|
Thanks for submitting your question to the MadSci network. Element symbols of the periodic table are not required to have two letters.
The elements Hydrogen (H), Boron (B), Carbon (C), Nitrogen (N), Oxygen (O), Flourine (F), Phosphorus (P), Sulphur (S), Potassium (K), Vanadium (V), Yttrium (Y), Iodine (I), Tungsten (W), and Uranium (U) all use one-letter symbols.
In addition, the elements 111 (Unununium, Uuu), 112 (Ununbium, Uub), and 116 (Ununhexium, Uuh) use three-letter symbols. Other elements, whose existances may or may not have been confirmed, like 113 (Ununtrium, Uut), 114 (Ununquadium, Uuq), 115 (Ununpentium, Uup), and 118 (Ununoctium, Uuo) also have three-letter symbols assigned to them. However, these elemental symbols are usually temporary until official two-letter symbols are assigned to them (usually representing the name of a famous scientist). For example, the name Roentgenium (symbol, Rg) has been proposed for element 111 (Uuu). You can read more about the IUPAC naming system for elements here (http://www.chemicalelements.com/sup/sysname.html).
If you think about it, if you were only allowed to use one letter of the alphabet to represent an element, you can only have 26 elemental symbols, because there are only 26 letters. After identifying the 27th element, you would have no symbol for it!
If you use a two-letter symbol, then you can have 26 X 26 or 676 unique symbols (I'll leave the exercise of writing out all of the two-letter combinations to you). If you use a three letter symbol, then you can have 26 X 26 X 26 or 17,576 unique symbols!!
You can find much more information about the periodic table of the elements, and the individual elements themselves on the WebElements.org web site.
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