s8pe-30803-ca
12/1/05
11:18 AM
MAZER
Page 258
KEY CONCEPT
Substances’ properties
depend on their bonds.
CALIFORNIA
Content Standards
8.3.c Students know
atoms and molecules
form solids by building
up repeating patterns,
such as the crystal
structure of NaCl or
long-chain polymers.
8.7.c Students know
substances can be
classified by their
properties, including
their melting temperature, density, hardness,
and thermal and electrical conductivity.
BEFORE, you learned
NOW, you will learn
• Chemical bonds hold the atoms
of compounds together
• Chemical bonds involve the
transfer or sharing of electrons
• Molecules have a structure
• How metal atoms form chemical bonds with one another
• How ionic and covalent
bonds influence substances’
properties
EXPLORE Bonds in Metals (8.7.c)
What objects conduct electricity?
PROCEDURE
1
VOCABULARY
Tape one end of a copper wire to one terminal
of the battery. Attach the other end of the
copper wire to the light bulb holder. Attach
a second wire to the holder. Tape a third wire
to the other terminal of the battery.
2 Touch the ends of both wires to objects around
metallic bond p. 258
MATERIALS
• masking tape
• 3 pieces of copper
wire (15 cm)
• D cell (battery)
• light bulb and
holder
• objects to test
the classroom. Notice if the bulb
lights or not.
WHAT DO YOU THINK?
• Which objects make the bulb light?
• How are these objects similar?
Metals have unique bonds.
reminder
Chemical bonds involve
the sharing of or transfer
of electrons.
258 Unit 3: Chemical Interactions
Metal atoms bond together by sharing their electrons with one another.
The atoms share the electrons equally in all directions. The equal
sharing allows the electrons to move easily among the atoms of the
metal. This special type of bond is called a metallic bond.
The properties of metals are determined by metallic bonds. One
common property of metals is that they are good conductors of
electric current. The electrons in a metal flow through the material,
carrying the electric current. The free movement of electrons among
metal atoms also means that metals are good conductors of heat.
Metals also typically have high melting points. Except for mercury, all
metals are solids at room temperature.
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