http://www.ck12.org Chapter 2. Matter
A:Calcium is a group 2 element with two valence electrons. Therefore, it is very reactive and gives up electrons in
chemical reactions. It is likely to react with an element with six valence electrons that “wants” to gain two electrons.
This would be an element in group 6, such as oxygen.
Valence Electrons and Electricity
Valence electrons also determine how well—if at all—the atoms of an element conduct electricity. The copper wires
in the cable in theFigure2.101 are coated with plastic. Copper is an excellent conductor of electricity, so it is used
for wires that carry electric current. Plastic contains mainly carbon, which cannot conduct electricity, so it is used as
insulation on the wires.
FIGURE 2.101
Q:Why do copper and carbon differ in their ability to conduct electricity?
A:Atoms of metals such as copper easily give up valence electrons. Their electrons can move freely and carry
electric current. You can see in detail how this occurs at the URL below. Atoms of nonmetals such as the carbon, on
the other hand, hold onto their electrons. Their electrons can’t move freely and carry current.
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/conins.html
A few elements, called metalloids, can conduct electricity, but not as well as metals. Examples include silicon
and germanium in group 14. Both become better conductors at higher temperatures. These elements are called
semiconductors.
Q:How many valence electrons do atoms of silicon and germanium have? What happens to their valence electrons
when the atoms are exposed to an electric field?
A:Atoms of these two elements have four valence electrons. When the atoms are exposed to an electric field, the
valence electrons move away from the atoms and allow current to flow.
Summary
- Valence electrons are the electrons in the outer energy level of an atom that can participate in interactions with
other atoms. - Because valence electrons are so important, atoms may be represented by electron dot diagrams that show
only their valence electrons. - The number of valence electrons in atoms may cause them to be unreactive or highly reactive. For those
atoms that are reactive, the number of valence electrons also determines whether they tend to give up or gain
electrons in chemical reactions. - Metals, which easily give up electrons, can conduct electricity. Nonmetals, which attract electrons, generally
cannot. Metalloids such as silicon and germanium can conduct electricity but not as well as metals.