s8pe-30802-ca
12/1/05
11:17 AM
MAZER
Page 256
Covalent Compounds
Unlike ionic compounds, covalent compounds come in individual
molecules. Chemical bonds give each molecule a specific, threedimensional shape called its molecular structure. Molecular structure
can influence how a specific substance feels and how well it bonds
with other substances.
A few basic molecular structures are shown below. Molecules
can have a simple linear shape, such as iodine. Or they can be bent,
such as a water molecule (H2O). The atoms in an ammonia molecule
(NH3) form a pyramid. Methane (CH4) molecules even have a slightly
more complex shape. A molecule’s shape can be extremely complex.
Some molecules contain thousands of atoms. You will learn more
about some very complex molecules in a later chapter.
reading tip
To help yourself appreciate
the differences among these
structures, try making threedimensional models of them.
H
I
H
H
Iodine
(I2)
N
O
I
water
(H2O)
H
H
C
H
H
ammonia
(NH3)
H
H
methane
(CH4)
Molecular shape can affect many properties of compounds. For
example, some scientists think we detect scents because molecules
with certain shapes fit into certain smell receptors in the nose.
Molecules with similar shapes, therefore, should have similar smells.
Molecular structure also determines how our bodies respond to certain drugs. Some drugs work because molecules with certain shapes
can fit into specific receptors in body cells.
KEY CONCEPTS
CRITICAL THINKING
1. What part of an atom is
involved in chemical bonding?
4. Analyze Would you expect
the bonds in ammonia to
be polar covalent? Why or
why not?
(8.3.a)
2. How are ionic bonds and
covalent bonds different? (8.3.a)
3. Describe two ways that crystal
and molecular structures affect
the properties of ionic and
covalent compounds. (8.3.c)
256 Unit 3: Chemical Interactions
5. Infer What kind of bond
would you expect atoms of
strontium and iodine to form?
Why? Write the formula and
name the compound.
CHALLENGE
6. Conclude Is the element
silicon likely to form ionic or
covalent bonds? Explain.
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