Study Guide 213
To find the number of valence electrons in an
atom of a representative element, simply look at its
group number.
A positively charged ion, or a cation, is produced
when an atom loses one or more valence electrons.
An anion is produced when an atom gains one or
more valence electrons.
valence electron r(194)
electron dot structure
r(195)
octet rule
r(195)
halide ion
r(199)
r
Although they are composed of ions, ionic
compounds are electrically neutra l.
Most ionic compounds are crystalline sol ids at
room temperature.
Ionic compounds generally have high melting
points.
Ionic compounds can conduct an electric current
when melted or dissolved in water.
ionic compound r(201)
ionic bond
r(201)
chemical formula
r(202)
formula unit
r(202)
coordination number
r(205)
The valence electrons of atoms in a pure metal can
be modeled as a sea of electrons.
Alloys are important bec ause their properties are
often superior to those of their component elements.
metallic bond r(209)
alloy
r(211)
Ions7.1
r
Ionic Bonds and Ionic Compounds7. 2
Bonding in Metals7. 3
BIGIDEA
BONDING AND INTERACTIONS
Atoms form positive ions (cations) by losing
valence electrons and form negative ions (anions)
by gaining valence electrons. The elec trostatic
forces between the oppositely charged ions hold the
cations and anions together in an ionic compound.
Ionic compounds generally have high melting
points and can conduct an electric c urrent in
solution and in the molten state. Metals are made
up of closely packed cations surrounded by a sea of
electrons. The sea-of-electrons model explains why
metals are good conductors of electric current and
why they are ductile and malleable.
7 Study Guide
Study Guide 213
STUDY GUIDE
Evaluate
Review and Assessment Materials
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PROBLEM SETS Have students practice
more formula writing problems by using
the Chapter 7 Online Problem Set.
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VIRTUAL LABS Have students complete
a virtual lab as an in-class or take-home
assignment to help reinforce the concept
of ionic bonding.
Study Tip
Write and answer questions about the content of the
chapter. For Chapter 7, you might ask the following
questions, which require students to summarize the
information contained in the chapter.
• What information does the electron dot structure
of an element provide? (the number of valence
electrons)
• In most cases, what is the stable electron
configuration of an elemental ion? (In most
cases, a stable configuration is characterized by
an octet of valence electrons; the configuration is
isoelectronic with that of a noble gas.)
• Why does NaCl dissolved in water conduct
electricity? (In water, the ionic compound breaks
apart into Na+ and Cl− ions that are free to move
in the solution.)
• What is the theory of bonding in pure metals?
(metal cations held together by a pool of mobile
valence electrons)
Performance Tasks
MODELING IONIC CRYSTALS Have students choose three ionic compounds and do
research to find out their crystal structures. Then have students use modeling clay
and toothpicks to make three-dimensional models of each crystal structure.
QUENCHING—NOT JUST FOR THIRST Alloys and metals are often quenched in water
after being heated and shaped. Have students research and report on the effects
of quenching on the crystalline structure of metals and alloys. Also, ask them to
compare the resulting crystals to ionic crystals. Reports should include any necessary
graphics and explain any changes in metal properties that occur as a result of the
quenching process.
