Page 16 - Theory and Problems of BEGINNING CHEMISTRY

CHAP. 1] BASIC CONCEPTS 5

Distinguishing a Mixture from a Compound
Let us imagine an experiment to distinguish a mixture from a compound. Powdered sulfur is yellow and
it dissolves in carbon disulfide, but it is not attracted by a magnet. Iron filings are black and are attracted by a
magnet, but do not dissolve in carbon disulfide. You can mix iron filings and powdered sulfur in any ratio and
get a yellowish-black mixture—the more sulfur that is present, the yellower the mixture will be. If you put the
mixture in a test tube and hold a magnet alongside the test tube just above the mixture, the iron filings will be
attracted, but the sulfur will not. If you pour enough (colorless) carbon disulfide on the mixture, stir, and then
pour off the resulting yellow liquid, the sulfur dissolves but the iron does not. The mixture of iron filings and
powdered sulfur is described as a mixture because the properties of the combination are still the properties of its
components.
If you mix sulfur and iron filings in a certain proportion and then heat the mixture, you can see a red
glow spread through the mixture. After it cools, the black solid lump that is produced—even if crushed into a
powder—does not dissolve in carbon disulfide and is not attracted by a magnet. The material has a new set of
properties; it is a compound, called iron(II) sulfide. It has a definite composition; and if, for example, you had
mixed more iron with the sulfur originally, some iron(II) sulfide and some leftover iron would have resulted. The
extra iron would not have become part of the compound.

1.6. REPRESENTATION OF ELEMENTS
Each element has an internationally accepted symbol to represent it. A list of the names and symbols of the
elements is found on page 349 of this book. Note that symbols for the elements are for the most part merely
abbreviations of their names, consisting of either one or two letters. The first letter of the symbol is always written
as a capital letter; the second letter, if any, is always written as a lowercase (small) letter. The symbols of a few
elements do not suggest their English names, but are derived from the Latin or German names of the elements.
The 10 elements whose names do not begin with the same letter as their symbols are listed in Table 1-2. For
convenience, on page 349 of this book, these elements are listed twice—once alphabetically by name and again
under the letter that is the first letter of their symbol. It is important to memorize the names and symbols of the
most common elements. To facilitate this task, the most familiar elements are listed in Table 1-3. The elements
with symbols in bold type should be learned first.

Table 1-2 Symbols and Names with Different
Initials

Symbol Name Symbol Name
Ag Silver Na Sodium
Au Gold Pb Lead
Fe Iron Sb Antimony
Hg Mercury Sn Tin
K Potassium W Tungsten

The Periodic Table
A convenient way of displaying the elements is in the form of a periodic table, such as is shown on page
350 of this book. The basis for the arrangement of elements in the periodic table will be discussed at length in
Chaps. 3 and 4. For the present, the periodic table is regarded as a convenient source of general information
about the elements. It will be used repeatedly throughout the book. One example of its use, shown in Fig. 1-1,
is to classify the elements as metals or nonmetals. All the elements except hydrogen that lie to the left of the
stepped line drawn on the periodic table, starting to the left of B and descending stepwise to a point between
Po and At, are metals. The other elements are nonmetals. It is readily seen that the majority of elements are
metals.