Symbols And Rules

Rules of Assigning Symbols
  
 Symbols can be denoted by the single letter, two letters & three letters. The symbols of elements are generally either the first or the first two letters or the first and the third letters of the name of the element.
1)An element is represented with the first letter in capital of the english name of the element.
For example, the symbols of the following elements are the first letter of the name of that element.

2)    When the names of two or more elements begins with the same initial letter, the letter followed by the next letter is used to represent the element

It is important to note that the first letter of every chemical symbol is capital letter but, if the symbol consists of two letters, the second letter is not capital letter, thus
Symbol for aluminium is Al and not AL 
Symbol for lead is Pb and not PB
Carelessness in writing symbols can lead to utter confusion.
For example,
"Co" is cobalt whereas "CO" is carbon monoxide. Therefore, if a person uses symbol CO for cobalt, the one who read  symbol will take it as carbon monoxide which is a compound of carbon and oxygen.  
Some symbols derived from the first and the third letters of the names of the elements.

3)There are certain symbols which seem to have no relationship to their names. The symbols of these elements are, in fact, derived from their latin names.

4)Elements named after scientists.

5)Some elements are named after planets.

List of Elements with Name, Atomic number and Symbol