3.2 – 3.4 Chemical Bonds, Formulas,
Molecular Models, and Atomic
Views of Elements and Compounds
Chemical Bonds
What is a chemical bond?
An attractive force that exists between charged particles; more specifically, between protons
and electrons of elements in a compound.
Name three types of chemical bonds, and explain the difference between all three.
Ionic bonds: a electrostatic force of attraction between a cations and anions. Usually, this is the
attraction between metals and nonmetals. Here electrons are transferred, and this results in an
ionic compound (solid lattice structure)
Covalent bonds: a force of attraction between nonmetals. Here some electrons are shared, and
the result is a molecule. The molecule whose structure shows the most equal distribution of
charge is the most stable, and results in that structure having lowest potential energy. In a
covalent bond, shared electrons are attracted to both positively charged nuclei of the bonding
atoms.
Metallic bonds: a force of attraction of metal cations and the mobile electrons between metal
atoms.
Chemical Formula
What is a chemical formula and how is it written
(which element comes first)? Give an example.
A way to represent a compound by the elements that
make it up. When writing a chemical formula, the
most metallic element (least electronegative) is
written first. MgCl2 is an example of a chemical
formula of an ionic compound.
Chemical Formulas (Continued)
There are generally three types of chemical formulas: 1.) Empirical formulas, 2.)
Molecular formulas, and 3.) Structural formulas. Describe each and give an
example.
Empirical formulas: Give the relative number (simplified or reduced) of atoms in
an compound. Example: The empirical formula of glucose is CH2O
Molecular formulas: Gives the actual number of the atoms of each element that
make up a compound. Example: The molecular formula of glucose is C6H12O6
Structural formula: uses lines to represent covalent bonds and shows how the
atoms in a molecule are connected or bonded to each other.
Example: Carbon tetrachloride (CCl4), has the following structural formula:
Cl
I
Cl– C–Cl
I
Cl
Molecular Models
• A more accurate way to represent a compound.
• Two types of molecular models are ball-and-stick models and
space-filling molecular models.
• In a ball-and-stick models, color coded ball represent different
atoms, and sticks represents the bonds that hold the atoms
together. This model also shows the geometry of the molecule.
• In a space-filling molecular model, atoms fill the space between
each other to give a better indication of what a molecule may look
like if scaled to visible size.
Examples of both models on next pg. 
An Atomic Level View of Elements and
Compounds
• Atomic elements: most elements in nature exist
with a single atom as their base unit (monatomic).
Example: He
• Molecular elements usually exist in nature as
molecules (most as diatomic molecules).
Which elements are diatomic in nature?
– The –gens (hydrogen, oxygen, nitrogen, and the
halogens)
Compounds
What is the difference between ionic and molecular
compounds?
Ionic compounds are made up of cations and anions
bound by ionic bonds. The basic unit of an ionic
compound is called a formula unit. Example: CaBr2
Molecular compounds are made up of two or more
covalently bonded nonmetals. The basic unit are
molecules. Example: water is made up of H2O
molecules
Polyatomic Ions
• Ions composed of two or more covalently bonded
atoms with an overall charge.
List three polyatomic ions:
CO32- (carbonate)
SO42- (sulfate)
PO43- (phosphate)
Pgs. 130-131 #’s 24, 26, 30, & 32
Read pgs. 95 - 106