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 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 use models to visualize a compound’s chemical structure Be able to describe how the chemical structure of a compound affects its properties 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 Chemically combined elements in specific amounts Example: NaCl = table salt Example: NaCl = table salt Violent Reaction

Compound Characteristics Chemical bonds distinguish compounds from mixtures Chemical bonds distinguish compounds from mixtures Chemical bonds are attractive forces that hold different atoms or ions together 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 They always have the same chemical formula, which tells how many atoms or ions of each element are in it Examples: H 2 0 = ___________________ Examples: H 2 0 = ___________________ C 12 H 22 O 11 = _________________ 2 hydrogen & 1 oxygen 12 carbon, 22 hydrogen & 11 oxygen

Compound Characteristics They have chemical structures that show the bonding within a compound They have chemical structures that show the bonding within a compound A chemical structure is the arrangement of atoms in a substance 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 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 Bond angle is the angle formed by two bonds to the same atom

Models of Compounds Three types of models: Three types of models: Structural Formulas Structural Formulas Ball-and-Stick Models Ball-and-Stick Models Space-filling Models Space-filling Models

Structural Formulas Show the structures of compounds using lines and chemical symbols 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 Show chemical structure by using balls for atoms and sticks for bonds

Space-Filling Models Show the space occupied by atoms in a compound Show the space occupied by atoms in a compound Doesn’t really show bond angles or lengths Doesn’t really show bond angles or lengths

How Does Structure Affect Properties? Strength of attractions Strength of attractions Melting points Melting points Boiling points Boiling points Ability to flow--viscosity Ability to flow--viscosity

Network Structure Compounds Compounds with network structures are strong solids Compounds with network structures are strong solids Example: quartz SiO 2 Example: quartz SiO 2  All the bond angles are the same  Have a high melting point & boiling point

Networks of Bonded Ions Compounds with this type of structures: 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 Example: NaCl

Compounds Made of Molecules For example: Sugar 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 Gases especially have very “loose” bonds because the molecules are not attracted to each other The strength of attractions between molecules varies: 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