H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
H2C
Chemical Formula
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
Like a word
• Describes Compounds
• Lists what elements are present in
the compound
• Expresses the ratio of each element
present
• Subscripts = how many atoms of
element to left of #.
H2C
Chemical Formula cont..
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
• Example:
CaI2
• The small 2 is a subscript. It
indicates that for each molecule of
calcium iodide, 1 atom of calcium is
present for each 2 atoms of iodine.
H2C
Chemical Formula Practice
CH2
H2C
CH2
H2C
CH2
H2C
H2C
H2C
How many atoms of nitrogen are
present? 1
How many
CH2 present?
How many
CH2
present?
CH2
H2C
Consider the formula for
potassium nitrate (KNO3):
atoms of potassium are
1
atoms of oxygen are
3
H2C
Your Turn…..
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
How many atoms of each element are
in each of the formulas below?
CaCl2
Pb2(CrO4)3
KCl
NH4NO2
MgBr2
Mg(NO3)2
Na2S
(NH4)2S
Sr3N2
Ca(NO3)2
H2C
Remember…….Ionic
CH
Compounds
2
H2C
CH2
H2C
H2C
H2C
• Composed of (+) cation and (-)
CH2 anion for a net charge of zero
• These charges are also called
CH2
“oxidation numbers”
CH2
H2C
CH2
H2C
H2C
CH2
Charges?
Cations:
H2C
H2C
H2C
H2C
•CH
Group
1 A = +1
2
• Group 2A = +2
2
•CH
Group
3A (metals (below the zig-zag line)) = +3
• Group 4A (metals (below the zig-zag line)) = +4
CH2
• Group 5A (metals (below the zig-zag line))= +5
•CH
Group
6A (metal (below the zig-zag line)) = +6
2
H2C
CH2
H2C
Charges? Cont…
H2C
CH2
Anions:
H2C
H2C
H2C
H2C
•CHGroup
8A = 0 (noble gases)
2
• Group 7A = -1
2
•CHGroup
6A = -2
• Group 5A (non metals (above the zig-zag line)) = -3
CH2
• Group 4A (non metals (below the zig-zag line)) = -4
•CHGroup 3A (non metals (below the zig-zag line)) = -5
2
H2C
CH2
H2C
H2C
IONIC Bonds in IONIC compounds!
• Remember our example…NaCl.
• What does ION mean?
CH2
Charged particles
CH2 • How do atoms become charged?
CH2
H2C
H2C
H2C
CH2
H2C
CH2
H2C
CH2
H2C
+++--+++---
gain or give away ELECTRONS
ZERO
• The whole compound has to equal
H2C
CH2
H2C
CH2
H2C
H2C
1.
Write each element’s symbol with
its charge = ion formula
CH2 2. Place the Cation (+) ion first and
then place the anion (-) second.
CH2 3. Move the superscript (charge of
H2C
CH2
H2C
CH2
H2C
How do I write Ionic
Compound Formulas ?
the first ion) to the bottom
(subscript) of the second ion.
H2C
CH2
H2C
How do I write Ionic
Compound Formulas ?
4. Make the subscripts positive (+).
CH2
Note: If the subscript is 1 then no
H2C
subscript is needed.
CH2
H2C
H2C
Double check: The charges X the # of
ions on each ion should add up to a net
CH2
charge of zero.
CH2
H2C
CH2
H2C
H2C
Lets Practice…
CH2
H2C
H2C
Cation
CH2
Na+
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
Write the formula for Sodium Oxide
Anion
O-2
=
Formula
Na2O
Na2O = 2 atoms of Na+ & 1 atom
of O-2
Na+ + Na+ + O-2 = 0
(+1) + (+1) + (-2) = 0
H2C
This is called the “criss-cross”
CH
method
2
H2C
H2C
Cation
CH2
Ca+2
Anion
Cl-1
CH2
Al+3
Cl-1
CH2
Li+1
N-3
CH2
Mg+2
N-3
H2C
H2C
H2C
CH2
H2C
=
Formula
Calcium
CaCl2 chloride
AlCl3
Aluminum
chloride
=
Li3N
Lithium
nitride
=
Mg3N
=
Magnesium
2 nitride
H2C
Your Turn…..Write the
CH Formula for aluminum sulfide
Cation
Anion
Formula
CH
Al2S3
Al+3
S-2 =
2
H2C
2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
Al2S3 = 2 atoms of Al+3 & 3 atom
of S-2
Al+3 + Al+3 + S-2 + S-2 + S-2 = 0
+3 + +3 + -2 + -2 + -2 = 0
H2C
What about transitional elements?
CH2 1.
H2C
H2C
If given the name, the charge is
provided with a Roman numeral
CH2 2. If given the formula, write the charge in
Roman numerals in parenthesis
CH2
H2C
H2C
CH2 copper (I) oxide = Cu+1 and O-2 = Cu O
2
+4 and O-2 = lead (IV) oxide
Pb
O
=
Pb
2 4
CH2
H2C
CH2
H2C
iron (II) oxide = Fe+2 and O-2 = FeO
H2C
Transitional elements are easy…
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
cobalt (III) chloride
gold (I) sulfide
lead (II) iodide
iron (III) oxide
chromium (II) sulfide
copper (II) chloride
lead (IV) iodide
CoCl3
Au2S
PbI2
Fe2O3
CrS
CuCl2
PbI4
H2C
Name these transitional elements
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
Mn2O4
Cr2O3
PbCl2
FeI3
Cr2S3
CuCl
PtI4
manganese (IV) oxide
chromium (III) oxide
lead (II) chloride
iron (III) iodide
chromium (III) sulfide
copper (I) chloride
platinum (IV) iodide
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
Polyatomic Ions
• Group of bonded atoms w/a charge
Place polyatomic ion in ( ) and treat as one
unit and place the subscript on the
outside of the ().
• If the polyatomic is taken only once then
() are not needed.
• Ex: (PO4)3Phosphate ion with 3- charge
Common Polyatomic ions
H2C
CH2
H2C + 1 charge
+
CH
NH
2 4
-1
-2
-3
OHCO3-2
PO4-3
H2C Ammonium Hydroxide Carbonate Phosphate
CH2
NO3SO4-2
H2C
Nitrate
Sulfate
CH2
NO2SO3-2
H2C
Nitrite
Sulfite
CH2
H2C
CH2
H2C
H2C
Lets Practice… Formula for
potassium carbonate
CH
2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
Cation
Anion
+
-2
K
(CO3)
+
K
+
K
(CO3
remove parentheses
Formula
= K2(CO3)
-2
=0
)
K2CO3
H2C
Formula for zinc nitrate
CH2
Cation
Anion
Formula
CH2
Zn+2
(NO3)-1
= Zn(NO3)2
H2C
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
Zn+2 (NO3)-1 (NO3)-1 = 0
What about Ionic Formulas with Polyatomics?
H2C
CH2
NH4 & Cl
CH2
Al & NO3
H2C
H2C
CH2
Ca & CO3
CH2
K & PO4
H2C
H2C
CH2
H2C
CH2
H2C
(NH4)2Cl
ammonium chloride
Al(NO3)3
aluminum nitrate
CaCO3
calcium carbonate
K2PO4
potassium phosphate
Let’s put it all together…
H2C
CH2 sodium hydroxide
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
NaOH
HgSO4
mercury (II) sulfate
Pb3(PO4)4
lead (IV) phosphate
(NH4)2S
ammonium sulfide
Al(ClO3)3
aluminum chlorate
Cu2CO3
copper (I) carbonate
manganese (IV) oxide Mn2O4
Al2(NO3)3
aluminum nitrate
FePO4
iron (II) phosphate
Na2CrO4
sodium chromate
ammonium chromate (NH4)2CrO4
How about the other way?
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
H2C
Ca(OH)2
PbSO4
Cu3(PO4)2
(NH4)2O
Al(BrO3)3
CuCO3
Mn2S4
Al2(SO4)3
Fe2(PO4)3
Li2CrO4
(NH4)2CO3
calcium hydroxide
lead (II) sulfate
copper (II) phosphate
ammonium oxide
aluminum bromate
copper (II) carbonate
manganese (IV) sulfide
aluminum sulfate
iron (III) phosphate
lithium chromate
ammonium carbonate