Elements Symbols Atomic Weights Gram Atomic Weights

Remembering the names of the common elements poses no particular problem to the average student. However, the proper symbol does not always come to mind. This is mainly because many of the symbols are derived from Latin, Greek, or German names of the elements, and sometimes because of a similarity of names which makes a multiple choice of symbols possible. This similarity is well illustrated by the symbols for magnesium, Mg, and manganese, Mn, which are commonly confused.

To remember the symbols for magnesium, manganese, and those derived from Latin or other foreign names, one must rely entirely upon memory or association with the uncommon name. A list of the elements whose symbols are derived from Latin, Greek, or German names is given in Table 2.1.

Atomic weights of the elements refer to the relative weights of the atoms as compared with some standard. In 1961 the 12C isotope of carbon was adopted as the atomic weight standard with a value of exactly 12. According to this standard, the atomic weight of oxygen is 15.9994, or 16 for all practical purposes.

It is not necessary to remember the atomic weights of the elements, because tables giving these values are readily available. It will save time, however, to remember the weight of the more commonly used elements such as hydrogen, oxygen, carbon, calcium, magnesium, sodium, sulfur, aluminum, chlorine, and a few others. It

Table 2.1 i List of elements with symbols derived from Latin, Greek, or German names

'Element

'' Name.frojn -vyhich 4 'symbol is"deri>ed

Antimony

Stibium, L,

Sb

Copper

Cuprum, L.

Cu

Gold

Aurium, L.

Au

Iron

Ferrum, L.

Fe

Lead

Plumbum, L.

Pb

Mercury

Hydrargyrum, Gr.

Hg

Potassium

Kalium, L.

K

Silver

Argentum, L,

Ag

Sodium

Natrium, L.

Na

Tin

Stannum, L.

Sn

Tungsten

Wolfram, G.

W

is usually sufficient for all practical purposes to round off the atomic weights at three significant figures: thus the atomic weight for aluminum is called 27.0, chlorine 35.5, gold 197, iodine 127, and so on.

In general, elements do not have atomic weights that are whole numbers because they consist of a mixture of isotopes. Chlorine is a good example. Its atomic weight of 35.45 is due to the fact that it consists of two isotopes with atomic weights of 35 and 37. Cadmium contains eight isotopes with atomic weights ranging from 110 to 116.

The gram atomic weight of an element refers to a quantity of the element in grams corresponding to the atomic weight. It has principal significance in the solution of problems involving weight relationships,

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