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Water for life
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6.2 Chemical symbols

So far, atoms have been represented as labelled spheres or circles and the bonds that link atoms in molecules have been represented as lines. This is a rather cumbersome method of writing down molecules. Chemists have developed their own shorthand language for the names of the elements. It involves giving each element a symbol consisting of one or two letters. You can guess some of them, because they start with the first letter of the element's name. Thus oxygen is designated by the capital letter O and nitrogen by N.

Question 22

The symbols of the following elements are all formed in this way: hydrogen, carbon and sulfur. Write down their symbols.


The chemical symbols are H for hydrogen, C for carbon and S for sulfur.

However, there are about 100 elements and only 26 letters in the alphabet! So some elements such as calcium and aluminium are represented by the first two letters. Thus calcium is Ca and aluminium is Al. Note that the first letter is always a capital and the second is always written or printed as a small letter (lower case).

Question 23

The symbols of the following elements are all of the type just described: helium, nickel, bromine and silicon. Write down their symbols.


The chemical symbols are He for helium, Ni for nickel, Br for bromine and Si for silicon.

This may seem perfectly straightforward but, for historical reasons, some elements have unusual symbols. Sulfur had taken the symbol S and so an alternative was required for sodium.

Table 5 shows the symbols for a few of the more common elements, along with the origins of the element's name. As noted above, in any two-letter symbol, the second letter is always lower case.

Table 5 Name, origin and symbol* for 15 elements
Element nameOrigin of nameSymbol
hydrogenfrom the Greek, hydro (water) and genes (forming)H
heliumfrom the Greek, Helios (the Sun)He
carbonfrom the Latin, carbo (charcoal)C
nitrogenfrom the Greek, nitron and genes (soda forming)N
oxygenfrom the Greek, oxys and genes (acid forming)O
sodiumfrom the English, soda (natrium in Latin)Na
magnesiumfrom Magnesia, a district of Thessaly in GreeceMg
aluminiumfrom the Latin, alumen (alum)Al
siliconfrom the Latin, silex (flint)Si
sulfurfrom the Latin name sulphur for the elementS
chlorinefrom the Greek, chloros (yellowish green)Cl
potassiumfrom the English, potash (symbol from kalium - Latin for alkali)K
calciumfrom the Latin, calyx (lime)Ca
ironAnglo-Saxon name for the metal; the Romans called it ferrumFe
brominefrom the Greek, bromos (stench)Br


*It is recommended that you memorise the chemical symbols for the 15 elements in Table 5. This will help you read and write the chemical shorthand used in chemical formulas (Section 6.3), and in chemical equations used to describe chemical reactions (Section 6.4).