2.6. Compounds http://www.ck12.org
A:Sodium chloride is an odorless white solid that is harmless unless consumed in large quantities. In fact, it is a
necessary component of the human diet.
Structure of Compounds
Compounds like sodium chloride form structures called crystals. Acrystalis a rigid framework of many ions locked
together in a repeating pattern. Ions are electrically charged forms of atoms. You can see a crystal of sodium chloride
in theFigure2.12. It is made up of many sodium and chloride ions.
FIGURE 2.12
A sodium chloride crystal consists of many sodium ions (blue) and chloride
ions (green) arranged in a rigid framework.You can actually watch a crystal forming (with time-lapse photography) at this URL: http://www.youtube.com/w
atch?v=Jd9C40Svt5g (1:09).
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/54904Compounds such as carbon dioxide and water form molecules instead of crystals. Amoleculeis the smallest particle
of a compound that still has the compound’s properties. It consists of two or more atoms bonded together. You saw
models of carbon dioxide and water molecules above. You can learn more about molecules at this URL: http://w
ww.nyscience.org/marvelousmolecules/marveloussub.html.
Summary
- A compound is a unique substance that forms when two or more elements combine chemically. A compound
always has the same elements in the same proportions. - The properties of compounds may be very different from the properties of the elements that form them.
- Some compounds form rigid frameworks called crystals. Other compounds form individual molecules. A
molecule is the smallest particle of a compound that still has the compound’s properties.
Vocabulary
- compound: Unique substance that forms when two or more elements combine chemically.
- crystal: Rigid, lattice-like framework of many ions bonded together that is formed by some compounds such
as table salt (NaCl).