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Writing
Chemical
Formulas
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Ionic Bonding and
Ionic Formulas
Tutorial and
questions
Ions
• When as atom gains or loses an atom is called an ion.
• Cation if positively charged or giving electrons away.
•
• Anion if negatively charged or accepting electrons.
How to predict charges with Lewis Dot
All elements move to have a full outer octet, like the
Noble Gasses.
An outer octet is made from 2 electrons in the s orbit
and 6 electrons in the p orbit.
Elements can gain or lose electrons to achieve 8
electrons in their valence shell.
H
+
H
+
e
=
e
More
Examples:
F +
N +3
e
+
4
C
e
C 
e
 F
 N
 C
4+
C +4e
34-
General Charges
X X
+1 +2
X X X X X X
Many
different
Charges
+4
+3
-3 -2 -1
-4
Many Different Charges
N
O
B
E
L
G
A
S
E
S
Writing Compounds:
Sodium and oxygen…
Na
O
Na+1 and O2These need to add together to equal zero.
One must lose electrons and the other must gain electrons.
So two sodium’s for every oxygen to equal zero.
2(+1) + (-2) = 0
2 Na+1 and O2-
This is written Na2O.
Example #2:
Barium and phosphorous
Ba
P
Ba2+ and P3These must add to equal 0.
Therefore 3 bariums and 2 phosphorous are
needed.
3(+2) + 2(-3) = 0
3 Ba2+ and 2 P3This is written Ba3P2
Polyatomic ions
• These are groups of atoms that hang around
together and have a charge.
Hydroxide ion
Ammonium ion
Here is a trick to name and know
about 48 polyatomic ions.
BO3 CO3 NO3
Now to name them…
Like the chart above
(base element name) –ate
1 more oxygen than above
Per -(base element name) – ate
1 less oxygen than above
(base element name –ite
2 less oxygen than above
Hypo –(base element name) - ite
-2
-1
O
F
PO4 SO4 ClO3
AsO4 SeO4 BrO3
SbO4 TeO4 IO3
Noble Gases
-3
-3
-2
-1
As is…
BO3 CO3 NO3
BO33- borate
CO32- carbonate
PO4 SO4 ClO3
–
NO3 nitrate
PO43- phosphate
AsO
SeO
BrO
4
4
3
2SO4 sulfate
Lose one oxygen
–
ClO3 chlorate… make you want SbO TeO IO
O
to fight…
NO2– nitrite
ClO2– chlorite
BO23- borite
CO22- carbonite
PO33- phosphite
SO32- sulfite…
4
F
4
3
Noble Gases
Polyatomics
Lose two oxygens and
you are out in the
cold but still want
to fight.
ClO– hypochlorite
BO 3- hypoborite
CO2- hypocarbonite
NO– hyponitrite
PO23- hypophosphite
SO22- hyposulfite…
-3
BO3 CO3 NO3
Gain one oxygen make
you want to per…
ClO4– perchlorate
BO43- perborate
CO42- percarbonate
NO4– pernitrate
PO53- perphosphate
SO52- persulfate…
-2
-1
O
F
PO4 SO4 ClO3
AsO4 SeO4 BrO3
SbO4 TeO4 IO3
Noble Gases
Polyatomics
Other polyatomics that you
should know are on the back
of your periodic table that
you were given.
Writing Formulas with polyatomics.
Let’s write the formula for sodium and phosphate.
Na+ PO4 3Remember that these must add to equal zero.
3 (+1) + 1 (-3) = 0
3 Na+ 1 PO4 3-
Na3PO4
Writing Formulas with polyatomics.
Let’s write the formula for calcium and nitrate.
Ca2+ NO3 Remember that these must add to equal zero.
1 (+2) + 2 (-1) = 0
1 Ca2+
2 NO3-
Because there are two nitrates needed to balance out the
charge of the calcium parenthesis are used to keep the
group together and denote that two groups of nitrate are
needed to balance the charge of the calcium.
Ca(NO3)2
Writing Formulas with polyatomics.
Let’s write the formula for barium and phosphate.
Ba2+
PO4 3Remember that these must add to equal zero.
3 (+2) + 2 (-3) = 0
3 Ba+
2 PO4 3-
Because there are two phosphates needed to balance out the
charge of three bariums parenthesis are used to keep the
group together and denote that two groups of phosphate
are needed to balance the charge of the three bariums.
Ba3(PO4)2
Writing Formulas with polyatomics.
Let’s write the formula for lead (IV) carbonate.
The Roman Number (IV) tells the charge of the lead. The Roman
number always tells the charge of the positive ion.
Pb4+
CO32Remember that these must add to equal zero.
Careful! This must happen with the lowest numbers possible!
1 (+4) + 2 (-2) = 0
1Pb4+
2 CO32-
Because there are two carbonate ions needed to balance out the
charge of on lead (IV) ion parenthesis are used to keep the group
together and denote that two carbonate ions are needed to
balance the charge of the lead (IV) ion .
Pb(CO3)2
Writing Formulas with polyatomics.
Let’s write the formula for aluminum and oxalate.
Al3+
C2O4 2Remember that these must add to equal zero.
2 (+3) + 3 (-2) = 0
2 Al3+
3 C2O4 2-
Because there are three oxalate ions needed to balance out
the charge of two aluminum parenthesis are used to keep
the group together and denote that three groups of oxalate
are needed to balance the charge of the two aluminum.
Al2(C2O4)3
Keep Practicing!
Keep Up! Don’t forget to take notes!