CK-12-Chemistry Intermediate

http://www.ck12.org Chapter 2. Matter and Change

solution. Sometimes it can be difficult to tell the difference between a compound and a homogeneous mixture based
solely on appearance. Consider gasoline. It is certainly homogeneous and seems a likely candidate for a compound,
meaning that it would have a fixed composition. However, as you may know, gasoline can be purchased at a station
in a variety of grades, such as regular or premium grade. Premium grades have a higher octane rating and cost more
than regular grades. Gasoline is thus a blend of different compounds, so it is a mixture.

Chemical Symbols and Formulas

Chemists use symbols and formulas as an abbreviated way of writing chemical reactions and the elements and
compounds involved in them. Achemical symbolis a unique one- or two-letter designation of an element. Some
examples of chemical symbols are O for oxygen, Zn for zinc, and Fe for iron. The first letter of a symbol is always
capitalized. If the symbol contains two letters, the second letter is lower case. The majority of elements have symbols
that are based on their English names. However, some of the elements that have been known since ancient times
have maintained symbols that are based on their Latin names (Table2.2).

TABLE2.2: Symbols and Latin Names for Various Elements

Chemical Symbol Name Latin Name

Na Sodium Natrium

K Potassium Kalium

Fe Iron Ferrum

Cu Copper Cuprum

Ag Silver Argentum

Sn Tin Stannum

Sb Antimony Stibium

Au Gold Aurum

Pb Lead Plumbum

As stated earlier, compounds are combinations of two or more elements. Achemical formulais an expression that
shows the elements in a compound and the relative proportions of those elements. For example, water is composed
of hydrogen and oxygen in a two to one ratio. The chemical formula for water is H 2 O. Sulfuric acid is one of the
most widely produced chemicals in the Unites States and is composed of the elements hydrogen, sulfur, and oxygen.
The chemical formula for sulfuric acid is H 2 SO 4.

Lesson Summary

• Mixtures are physical blends of two or more pure substances and can either be homogeneous or heterogeneous.
  Mixtures can be separated into their components by physical means such as filtration or distillation.


• Pure substances may be either elements or compounds. Elements are the simplest types of matter, while a
  compound is a chemical combination of two or more elements. A compound may only be decomposed into
  its elements by a chemical process.


• Chemical symbols and formulas are used to represent elements and compounds.