Chapter 3 Molecules, Compounds, and Chemical Equations.
Compounds are composed of atoms held together by chemical bonds. Chemical bonds are the
result of interaction between the charged particles electrons and protons that compose atoms.
There are 2 types of bonds we will focus on ionic and covalent.
Ionic Bonds- occur between metals and nonmetals involving the transfer of electrons from one
atom to the other.
Covalent Bonds- occur between two or more nonmetals involving the sharing of electrons
between 2 atoms.
Metals have a tendency to lose electrons and that nonmetal have a tendency to gain them. When
a metal interacts with a nonmetal it can transfer one or more of its electrons to the nonmetal.
The metal becomes a cation which is positively charged and the nonmetal becomes an anion a
negatively charged ion.
These oppositely charged ions are then attracted to one another by electrostatic forces and form
and ionic bond.
When a nonmetal bonds with another nonmetal, the atoms are sharing their electrons. The shared
electrons interact with both nuclei, lowering the potential energy.
The most stable covalent bond with the lowest potential charge looks like this. It has the lowest
potential energy because the negative charge can interact with both positive electrons. The
negative charges lies between the 2 positive charges. Shared electrons in a covalent chemical bond hold the bonding atoms together by attracting the
positively charged nuclei of both bonding atoms. Chemical Formulas:
Chemical formula- indicates which elements are present in the compound and the relative
number of atoms or ions of each. 2 O
Empirical Formula- gives the relative number of atoms of each element in each compound.
Basically the simplest ratio.
Molecular formula- gives the actual number of atoms of each element in a molecule of a
H 2 2
The molecular formula is always a whole-number multiple of the empirical formula.
These are the formula for hydrogen peroxide.
Atomic scale of Elements and Compounds:
Atomic elements- are those exist in nature with single atoms as their basic units.
He, Li, and Be. Basically, anything that’s not polyatomic or diatomic.
Lithium would be composed of lithium Ions.
Molecular Elements- these elements don’t normally exist in nature with single atoms as their
basic units. They exists as molecules two or more atoms of the element bonded together.
Most of these molecular elements exist of diatomic molecules.
Hydrogen, oxygen, nitrogen, chlorine all exist as diatomic.
H 2 O2 N 2
Some molecules will exist as polyatomic molecules like phosphorus and Sulfur.
P4 S 8 Molecular Compounds- are usually composed of two or more covalently bonded nonmetals. The
basic units of molecular compounds are molecules composed of the constituent atoms. Like
water or carbon dioxide.
Ionic Compounds- are composed of cations and anions. A Metal and Nonmetal bound together
by an ionic bond. They are electrically neutral.
Polyatomic Ions- A polyatomic ion, also known as a molecular ion, is a charged chemical
species (ion) composed of two or more atoms covalently bonded or of a metal complex that can
be considered to be acting as a single unit.
These ions are not neutral and will have some sort of charge.
This is a popular polyatomic ion ClO Hypochlorite. The # of oxygen molecules will change
giving it a different name. The charge always stays -1.
Writing Formulas for Ionic Compounds:
Remember the compound will be electrically neutral.
Ionic compounds always cancel and the sum of cation ions must equal the sum of anion ions.
Al & O
Al2O 3 Aluminum: 2(3+)= 6+
Oxygen : 3(2-)= 6- the charges will cancel.
Naming Ionic compounds:
An ionic compound is a metal and nonmetal.
There are 2 types: the metal will form only one type of ion.
The metal forms more than one type of ion. To Name An Ionic Compound With Only One Type Of Cation:
Name of cation (metal) Base name of Anion (nonmetal) + -ide
KCl This is Potassium(+1) and Chlorine(-1) the correct name is Potassium Chloride
CaO Calcium (2+) Oxygen (2-) Charges cancel and the name is Calcium Oxide.
Common Monoatomic Anions:
Non-metal Symbol for Ion Base Name Anion Name