Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
27
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER
3
3.4 Elements and Compounds
Pure substances are classified into two categories—elements and compounds. An element is a substance that cannot be separated into
simpler substances. Oxygen, carbon, sulfur, aluminum, iron, and gold
are elements. More than 110 elements are known, but only 91 occur
naturally on Earth. The remainder have been created by scientists.
Each element may be represented by a one- or two-letter symbol. In the mid-nineteenth century, a Russian chemist, Dmitri
Mendeleev, saw that elements could be arranged according to
repeating patterns of properties. Mendeleev’s arrangement has
evolved into the periodic table of the elements that you can see
inside the back cover of this Handbook. The vertical columns of elements are called groups or families. The elements in a group have
similar properties. Horizontal rows on the periodic table are called
periods. When a new period starts, the elements tend to repeat the
properties of the elements above them in the previous period. The
value of Mendeleev’s table was that it correctly predicted the properties of elements that had not yet been discovered.
A compound is a substance that consists of two or more elements chemically combined. The elements in a compound are not
simply mingled together as they are in a mixture. Instead, they are
combined in a way such that the compound has properties that are
different from those of the elements of which it is composed. Each
compound is represented by a formula, a combination of the symbols of the elements that make up the compounds. You may already
know some chemical formulas such as H 2 O for water, NaCl for table
salt, and NH 3 for ammonia.
Practice Problems
9. Identify each of the following as an example of an element or a
compound.
a. sucrose (table sugar)
b. the helium in a balloon
c. baking soda
d. a diamond
Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
27
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER
3
3.4 Elements and Compounds
Pure substances are classified into two categories—elements and compounds. An element is a substance that cannot be separated into
simpler substances. Oxygen, carbon, sulfur, aluminum, iron, and gold
are elements. More than 110 elements are known, but only 91 occur
naturally on Earth. The remainder have been created by scientists.
Each element may be represented by a one- or two-letter symbol. In the mid-nineteenth century, a Russian chemist, Dmitri
Mendeleev, saw that elements could be arranged according to
repeating patterns of properties. Mendeleev’s arrangement has
evolved into the periodic table of the elements that you can see
inside the back cover of this Handbook. The vertical columns of elements are called groups or families. The elements in a group have
similar properties. Horizontal rows on the periodic table are called
periods. When a new period starts, the elements tend to repeat the
properties of the elements above them in the previous period. The
value of Mendeleev’s table was that it correctly predicted the properties of elements that had not yet been discovered.
A compound is a substance that consists of two or more elements chemically combined. The elements in a compound are not
simply mingled together as they are in a mixture. Instead, they are
combined in a way such that the compound has properties that are
different from those of the elements of which it is composed. Each
compound is represented by a formula, a combination of the symbols of the elements that make up the compounds. You may already
know some chemical formulas such as H 2 O for water, NaCl for table
salt, and NH 3 for ammonia.
Practice Problems
9. Identify each of the following as an example of an element or a
compound.
a. sucrose (table sugar)
b. the helium in a balloon
c. baking soda
d. a diamond