Objectives
Be able to relate the chemical formula of a
compound to the relative numbers of atoms
or ions present in the compound
 Be able to use models to visualize a
compound’s chemical structure
 Be able to describe how the chemical
structure of a compound affects its
properties

Important Vocabulary
 Compound
 Chemical
bond
 Chemical formula
 Chemical structure
 Bond length
 Bond angle
 Structural formula
 Ball-and-stick model
 Space-filling model
What are Compounds?
Chemically combined elements in specific
amounts
 Example: NaCl = table salt

Violent Reaction
Compound Characteristics
Chemical bonds distinguish compounds from
mixtures
 Chemical bonds are attractive forces that
hold different atoms or ions together
 They always have the same chemical formula,
which tells how many atoms or ions of each
element are in it
2 hydrogen & 1 oxygen
 Examples: H20 = ___________________

12 carbon, 22 hydrogen
C12H22O11 = _________________
& 11 oxygen
Compound Characteristics
They have chemical structures that show the
bonding within a compound
 A chemical structure is the arrangement of
atoms in a substance
 Bond length is the average distance between
the nuclei of the 2 bonded atoms
 Bond angle is the angle formed by two bonds
to the same atom

Models of Compounds
 Three
types of models:
 Structural
Formulas
 Ball-and-Stick
 Space-filling
Models
Models
Structural Formulas

Show the structures of compounds using
lines and chemical symbols
Ball-and-Stick Models

Show chemical structure by using balls for
atoms and sticks for bonds
Space-Filling Models
Show the space occupied by atoms in a
compound
 Doesn’t really show bond angles or lengths

How Does Structure Affect
Properties?

Strength of attractions

Melting points

Boiling points

Ability to flow--viscosity
Network Structure Compounds


Compounds with network
structures are strong solids
Example: quartz SiO2
 All the bond angles are
the same
 Have a high melting point
& boiling point
Networks of Bonded Ions
Compounds with this type of
structures:
 Are ions of opposite
charges tightly bonded
together
 Form regular shaped
crystals
 Have high melting and
boiling points
 Example: NaCl

Compounds Made of Molecules
For example: Sugar
 Is made of carbon, hydrogen, & oxygen
 The bonds between them are not strongly
attracted
 Gases especially have very “loose” bonds
because the molecules are not attracted to
each other
 The strength of attractions between
molecules varies:
 Solids are stronger than liquids and liquids
are stronger than gases

Hydrogen Bonds

Are the attractive forces between water
molecules