Naming and Writing Formulas
for Binary Ionic and
Covalent Compounds of
Representative Elements.
Ionic Compound:
Compound must
have a metal and a
nonmetal!!!
Ex: NO, MgCl2, or
nitrogen monoxide,
magnesium chloride
Covalent Compound:
No evidence of a Metal
in the name nor
formula
Naming:
Writing Formula:
1. When naming ionic
compounds when given the
name there is no way to
determine how many of
each atom there is unless
you use oxidation numbers
2. Remember Oxidation
numbers go in the
following order: +1, +2,
+2, +3. +- 4, -3, -2, -1
3. Use the criss-cross of
oxidation numbers to write
the formula
Naming:
Naming Ionic Compounds is
easy. Use the example MgCl2
1. Write the complete name
of the metal first
Magnesium
2. Write the nonmetal
second and change the
ending to ide
Magnesium chloride
Writing Formula:
1. When you write the formula
for a covalent bond, simply
look at the prefixes of the
name and write that # in the
formula after the Symbol
1.
Use one of the prefixes in the
chart below for each word to
tell how many of them there is.
a. Never use the prefix
“mono” on the first word.
b. nitrogen monoxide
2.
Always change the ending of
the second word to ide.
a. Ex. Chlorine = Chloride
b. Oxygen = oxide
Ex: Dicarbon octahydride
C2O8
2. If you do not see a prefix on
the first word, know that this
means 1. Because we don’t
use mono prefix on first
word mono is not there.
Ex: Nitrogen monoxide
NO
Covalent Compounds
Only
Prefix
# of Atoms
Mono
Di
Tri
Tetra
Penta
Hexa
Hepta
Octa
1
2
3
4
5
6
7
8
4 Rules to remember when using Ionic Compounds
Rules for naming Ionic Formulas
Rule 1: Check to make sure that it is an Ionic Formula. (Always do this first) Use the following example of identifying formulas MgCl2 and NO
 does it have a metal and a non-metal. [NaCl does have a metal (Na) and a nonmetal (Cl) = Ionic]
 but [NO does not have a metal, it has two nonmetals (N & O)] you would need to use the covalent rules for this compound!!!!
Rule 2: Now that you have identifies the formula as IONIC, writing the name is easy. Just remember for Ionic compounds you DO NOT use prefixes.
Suppose you are given the formula MgCl2 and are prompted to name it.
1st : write the metal name = magnesium
2nd : write the nonmetal name and change the ending to ide = chloride
Finally: put them together = magnesium chloride
Rules for writing formulas of Ionic Compounds when given the name.
Rule 3: If you are trying to go from ionic name to molecular formula then follow these steps.
3a… Ionic bonds always exist in an exact ratio, but prefixes are not used with ionic bond names to show how many ions of elements are needed to fulfill this ratio;
therefore we must do the following…
3b… Separate out the different components of the formula ex:
3c… Now write the oxidation numbers for each Ion:
Na+1
3d… now crisscross oxidation numbers and write your formula:
Sodium Chloride
and
Na
and
Cl
Cl-1
Na+1
and
Cl-1
= Na1Cl1 = NaCl
Rule 4: Remember to relax and work step-by-step, absolutely do not ever try to skip steps.
Rules for Naming Covalent Compounds
Rule 1: Always make sure that your formula is Covalent. See the example found in Rule 1 of Ionic Naming.
Rule 2: Once you are sure your formula represents a covalent compound you are ready to name it. Use a prefix to tell us how many of each atom there is in the
compound.
Example: C2O4
2a: We would use the prefix di for carbon [dicarbon] this tells us that there is two carbons
2b: We would use the prefix tetra for oxygen [tetraoxygen] this tells us that there is four oxygens
2c: We would change the ending of the second word to ide [oxygen  oxide] because this is just the way its done.
2d: Now we would write it all together and get the name: dicarbon tetraoxide
2e: Never use the prefix mono on the first word!! For example, for the compound NO : the name = nitogen monoxide
Rues for writing the formulas for covalent compounds.
Rule 3: Always makes sure the compound is covalent (no metals in the name)
3a Use the prefixes in the name to identify how many of each atom are present in the compound.
3b Write the numerical value of the preix AFTER the symbol of the atom. See the example below
Dicarbon octahydride:
There are 2 carbons and 8 hydrogens
Therefore the formula must be C2H8