Warm Up: To be Turned in
Predict the molecular shape for the following
compounds:
CCl4
CO2
Chemical Names and Formulas
Significance of Chemical Formulas
 Some compounds are better known by their
common names
 Provides no information about the chemical
 Ionic compounds- represents one formula unit—the
simplest ratio of the compound’s cations and anions
EX:
Al2(SO4)3 Subscript 3 refers to everything inside
parentheses giving 3 sulfate ions, with
a total of 3 sulfur atoms and 12
oxygen atoms.
Subscript refers to 2
aluminum atoms.
Subscript refers to 4
oxygen atoms.
Assigning Oxidation numbers
 Based on the movement of electrons between atoms
 Groups 1, 2, and 13 have oxidation numbers of +1,
+2, +3, respectively
 Groups 15,16,17 have oxidation numbers of -3, -2,
-1, respectively
Writing Ionic Chemical Formulas
 Write the atoms side by side along with their
oxidation numbers, starting with the metal
3+
2Al O
 Cross over the oxidation numbers by using the
absolute value of each atom’s oxidation number as
the subscript for the other ion.
3+
2−
Al2 O3
Writing Ionic Chemical Formulas, Cont.
 Multiply the oxidation number by the number of
atoms for each part of the formula. The two number
should be equal but opposite in value.
Al23+O32−
(2 × 3+ = 6+)
(3 × 2- = 6-)
Al2O3
Naming Ionic Compounds
 Two part name
 Write the metal first
 Write the nonmetal second
 Drop the original ending and replace with –ide
 Ex: MgCl2 = magnesium chloride; KI= potassium
iodide
Transition Metals
 Some transition metals (Fe, Cu, Pb, Sn, Cr, etc.) can form
ions with more than one possible charge
 We identify the various compounds using the Stock System.
 Write a Roman Numeral immediately after the metal
 Ex: FeO = Iron(II) oxide; SnO2 = Tin(IV) oxide
Polyatomic ions
 Ions formed by more than one atom
 Naming system: write the metal followed by the name of the
polyatomic ion (except for NH4+, which is always names
first)
 Ex: NaNO3 = sodium nitrate
+1
-1
-2
-3
Ammonium NH4+
Acetate C2H3O2-
Carbonate CO32-
Phosphate PO43-
Cyanide CN-
Chromate CrO42-
Hydroxide OH-
Dichromate Cr2O72-
Nitrate NO3-
Sulfate SO42-
Nitrite NO2-
Sulfite SO32-
Perchlorate ClO4Permanganate MnO4-
Homework: Due 10/30/2012
Write formulas for the compounds formed between the following
atoms:
 aluminum and
bromine
 sodium and oxygen
 magnesium and iodine
 Pb2+ and O2−
 Sn2+ and I−
 Fe3+ and S2−
 Cu2+ and NO3−
 NH4+ and SO42−