Atoms, Elements, and
Compounds
Chapter Fifteen: Molecules and
Compounds
• 15.1 Compounds and Chemical Bonds
• 15.2 Electrons and Chemical Bonds
Investigation 15B
Molecules and Compounds
• What are some molecules and compounds
and what atoms are in them?
15.2 Electrons and chemical
bonds
• Chemical bonds are formed only between the
electrons in the highest unfilled energy level.
• These electrons are called valence electrons.
15.2 Electrons and chemical
bonds
• Going from left to right across a period
each new element has one more valence
electron than the one before it.
How many valence electrons does nitrogen have?
15.2 Lewis dot diagrams
• A clever way to keep
track of valence electrons
is to draw Lewis dot
diagrams.
• A dot diagram shows the
element symbol
surrounded by one to
eight dots representing
What is the dot
the valence electrons.
structure for nitrogen?
15.2 Oxidation numbers
• An oxidation number indicates the charge
on the remaining atom (ion) when electrons
are lost, gained, or shared in chemical bonds.
• A sodium atom always ionizes to become
Na+ (a charge of +1) when it combines with
other atoms to make a compound.
• Therefore, we say that sodium has an
oxidation number of 1+.
What is the most common oxidation
number for nitrogen?
15.2 Predicting a chemical formula
• When elements combine in molecules and
ionic compounds, the total electric charge is
always zero.
15.2 Ionic and covalent bonds
• On the periodic table, strong electron donors
are the left side (alkali metals).
• Strong electron acceptors are on the right
side (halogens).
• The further apart two elements are on the
periodic table, the more likely they are to form
an ionic compound.
15.2 Ionic and covalent bonds
• Covalent compounds form when elements
have roughly equal tendency to accept
electrons.
• Elements that are both nonmetals and
therefore close together on the periodic table
tend to form covalent compounds.
Technology Connection
Spiderman’s Favorite Compound
• The physical properties
of gold make it useful in
surprising ways.
• You can find gold in
astronaut gear, airplane
windshields, and even in
some people’s eyelids!
Activity
Plastics and Evaporation
• Plastic wrap has many household uses.
• In this activity, you will investigate different
polymers used in plastic wrap.