Transcript Section 3: Writing Formulas and Naming Compounds

Chapter 20: Chemical Bonds
SECTION 3: WRITING FORMULAS AND
NAMING COMPOUNDS
BINARY IONIC COMPOUNDS

Binary compound- one that is composed of 2
elements
 Example:

KI, NaCl
But before you can write these we have to know
a few pieces of information…
WHAT WILL I NEED TO KNOW TO WRITE AN IONIC FORMULA?

Are electrons gained or lost?
 When
you know this…you can figure out the
oxidation number- tells you how many electrons an
atom has gained, lost, or shared to become stable
(IT’S THE CHARGE)
 Example:
Na has an oxidation # of +1
 When something looks like this: iron(III) oxide, the roman
numeral is the oxidation number of iron
 But…compounds
 Example:
are neutral
CaF2 and Al2O3
OXIDATION NUMBERS
WRITING IONIC FORMULAS
1. Always write the positive ion first (metal)
followed by the negative ion (nonmetal)
 2. (Hint) The charge of one ion (without the
sign) becomes the subscript of the other ion

 Example:
You choose
WRITING NAMES OF IONIC COMPOUNDS



1. Write the name of the positive ion
2. Use table 2 in your book to see if the positive ion is
capable of forming more than one oxidation number. If
so, determine the charge it is using by looking at the
negative ion (only have 1 possible charge)
3. Write the root name of the negative ion

Example: Chlor- for chlorine and ox- for oxygen

4. Add the ending –ide to the root

Example: Tell me the name of BaF2
COMPOUNDS WITH COMPLEX IONS

Not all compounds are binary
 Example:
NaHCO3
 Contains
a polyatomic ion- a positively or negatively
charged, covalently bonded group of atoms
 Table of these on p. 619
COMMON POLYATOMIC IONS
WRITING NAMES AND FORMULAS FOR
COMPOUNDS WITH COMPLEX IONS

Writing Names
1. Write the name of the positive ion
 2. Use Table 4 p.619 to find the name of the polyatomic
ion
 3. Write the name of the negative ion

 Examples:

K2SO4 and Sr(OH)2
Writing Formulas

Follow the rules for binary compounds, except when
more than one polyatomic ion is needed, write
parentheses around the polyatomic ion before adding
the subscript
 Example:
Barium chlorate
COMPOUNDS WITH ADDED WATER

Some ionic compounds have water molecules
as part of their structure
 Called
hydrates- a compound that has water
chemically attached to its ions and written into its
chemical formula

Naming
 Example:
CaSO4
2 H2O
NAMING BINARY COVALENT COMPOUNDS
Remember, covalent compounds are formed
between elements that are nonmetals
 Using Prefixes

 We
use prefixes to
indicate the number
of atoms of each
element are in the
Compound
 Example:
N2O5