Writing, Dissociating and Naming Ionic Formulas
IONS → FORMULAS
To write Neutral Binary Formulas from Ions
1
Write the two ions side-by-side, cation first,
without the charges.
Example
Aa+ + Bb- → ________
1
Aa+ + Bb- → A B
2
2
Aa+ + Bb- →
3
Aa+ + BOxb- →
3
Determine how many of each ion are needed to
create a neutral formula, write that number as a
subscript. [Typically this is done by criss-crossing
and reducing the charges.]
Note that if a polyatomic ion is used, the subscript
is written outside of ( )’s
FORMULAS → IONS
Dissociating Neutral Binary Formulas Into Ions
AbBa
Ab(BOx)a
Al3+ + OH1- → Al1(OH)3
note that you do not have to write the 1’s, but it helps
Example
AbBa →
___ + ___ or
Ab(BOx)a → __ + __
Ab(BOx)a →
1 Split the formula into two “halves”. Often this is
done by writing the first symbol as the first half and
the remaining symbols as the second half. Do NOT
write any subscripts unless they are inside ( )’s or
follow two capital letters (see example)
1
AbBa →
A + B
2 The first ion is positive the second is negative.
2
AbBa →
A
3 Now determine the magnitude of the charge. Do
the opposite of “Ions to formulas” by criss-crossing
the subscripts into the position of charges.
3/4 AbBa →
+
+ B
or
-
Aa+ + Bb-
A + BOx
+
A
or Ab(BOx)a →
Aa+ + BOxb-
+ BOx
4 To make sure you are right (and often you are not)
you need to check your charges with the periodic
4 Examples of Checking Charges
table or with the charges on the polyatomic ions you Cu2O → Cu1+ + O2were to memorize.
Note the charge for O matches the periodic table. So we assume
the charges are correct.
Trend For Charges
For simple compounds, any element within the vertical
family headed by the following s and p block elements
will have the corresponding charge.
H1+, Be2+, B3+, C4+/4-, N3-, O2-, F1-, He no charge
K2SO4 →
-
or Ab(BOx)a →
K1+ + SO42-
Note the charge for K and SO4 matches the periodic table and the
memorized charge, so we assume the charges are correct.
Also note, the subscript “4” was not criss-crossed. The invisible
“1” outside the invisible “( )’s” was criss-crossed. The “4” follows
two capital letters and stays put.
For more complex compounds (AP Chem), the rules for CuO → Cu1+ + O1determining oxidation numbers must be followed.
Note that the charge for O should be a 2- from the periodic
.
table. So, we must double all charges to get it from 1- to 2-.
So...
CuO → Cu2+ + O2NAMES → FORMULAS
To write Neutral Binary Formulas from Names
Example: Write the formula of sodium sulfate
sodium = Na1+
1 Write the symbols for the corresponding cation and anion 1,
sulfate = SO422 Write the formula using the first table
2
Na1+ + SO42- → Na2SO4
“IONS → FORMULAS”
Writing, Dissociating and Naming Ionic Formulas
NAMING IONS and NAMING BINARY IONIC COMPOUNDS
Naming Binary Ionic Compounds
Example
You never name formulas. Name ONLY ions!! So if
you are given a formula to name you must first
dissociate it into ions and then name the ions.
or
If you are given a name and asked to write a
formula, you must first write the ions and then
write the formula.
Naming Cations
if s- or p-block elements
The name is the elemental name.
if d-block elements
The name is the elemental name followed by the
charge as a Roman numeral in parentheses.
Naming Cations
if s- or p-block elements
Li1+
lithium.
Al3+
aluminum
if d-block elements
Ni2+
nickel (II).
Ni3+
nickel (III)
Naming Anions
if mono-atomic (only one elemental symbol)
Then the name is the elemental name, but with the
ending changed to –ide.
Naming Anions
if monatomic:
F1fluoride (not fluorine)
O2oxide
(not oxygen)
As3- arsenide (not arsenic)
if polyatomic (more than one elemental symbol)
Then the name is the memorized name.
if polyatomic: These are the names to memorize
C2H3O21- acetate
CO32carbonate
1CN
cyanide
OH1hydroxide
NO31nitrate
1NO2
nitrite
SO42sulfate
SO32sulfite
3PO4
phosphate
PO33phosphite
Note that there exists one polyatomic cation that should
be memorized.
NH41+ is ammonium
All other cations will be one elemental symbol.
To name a formula
To name a formula
1
2
ex. Write the name of CuCO3
1
CuCO3 → Cu2+ + CO322
Cu2+ = copper (II)
CO32- = carbonate
so, the name is copper (II) carbonate
Dissociate into ions, then
Name the cation followed by the anion.