ELEMENTS ATOMIC WEIGHTS MOLECULES, ETC. 5 



that they seem to have lost the chemical affinities which 

 are characteristic of atoms. The number of atoms in a 

 molecule of an element when it is in the solid condition 

 is not known. 



6. Symbols. For the sake of convenience, each element 

 is represented by one or more letters. This abbreviation 

 of the name of an element is called its symbcl. The letter 

 used to represent an element is often the first letter of its 

 name. It is written as a capital, but unlike other abbre- 

 viations, it is not followed by a period. The symbol of 

 oxygen is O, of hydrogen is H, of nitrogen is N, and P 

 is the symbol of phosphorus. When the name of more 

 than one element begins with the same letter, the most 

 important or the first discovered of these elements has the 

 single letter for a symbol and to the others an additional 

 letter is assigned. Thus C is the symbol for carbon, Ca 

 the symbol for calcium, Cl the symbol for chlorine, Cr for 

 chromium. It will be noted that the second letter is not 

 written as a capital. Sometimes the symbol is derived from 

 the foreign word which means the element, as Fe from 

 the Latin ferrwn, meaning iron, K from Kalium, the Ger- 

 man word meaning potash, which contains potassium, 

 Hg from the Greek, hydrargyrum, meaning " w T ater silver," 

 a good description of mercury. Many symbols are taken 

 from the names of countries, as Cu, copper, from the island 

 bf Cyprus, Mg, magnesium, from Magnesia in Asia 

 Minor. The symbol of an element represents not only 

 the name of the element, but it means also one atom of 

 the element and consequently is a definite weight. S 

 stands not only for sulphur, but for one atom of sulphur, 

 which weighs 32, or two times the weight of an atom of 

 the standard, oxygen. 



7. Molecular Weights. One method for determining 

 molecular weights depends upon an hypothesis proposed 

 by Avogadro, which has been quite universally accepted. 

 This hypothesis states that " under the same conditions 



