CHEMICAL FORMULAS
Chemical Formulas
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A chemical formula provides the clearest and simplest
method of designating compounds.
It indicates the number and kind of elements present in the
compound.
Compounds that consist of two elements are called binary
compounds.
Binary Compounds
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AlCl3
NaCl
MgO
CO2
LiH
General Rules for Oxidation Numbers
1.
2.
3.
4.
5.
6.
Charge on pure elements is _______.
All metals of Group IA are ________.
All metals of Group IIA are _______.
The charge on all elements in Group IIIA is _____ except Tl
which can also be ____.
The charge on hydrogen is ___or __.
The charge on fluorine is ____.
General Rules for Oxidation Numbers
7. Other halogens (VIIA) are ____ except when combined with oxygen.
Then they are +.
8. Group IVA elements are ___ when negative.
9. Group VA elements are ____ when negative.
10. Group VIA elements are ___ when negative.
Polyatomic Ions Memory Work
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Ammonium_______
Acetate__________
Nitrate__________
Hydroxide_______
Cyanide_________
Carbonate_______
Sulfate__________
Phosphate________
Writing Formulas of Compounds
1. Write the symbol for the positive element first.
 The element name with the ending changed to -ide indicates
the element with a negative oxidation number.
Writing Formulas of Compounds
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Examples:
Oxide = ________
Chloride = ______
__________ = S2-
telluride = ________
hydride = ________
__________ = P3-
Writing Formulas of Compounds
2.
Use subscripts to make the formula contain the number of
atoms required for a neutral formula unit.
Example:
sodium chloride
Na1+ Cl11+1- = 0
NaCl
Writing Formulas of Compounds
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calcium chloride
sodium oxide
Writing formulas of compounds
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Magnesium nitride
potassium hydride
Writing formulas of compounds
3.
If more than one polyatomic ion appears in the formula
put the polyatomic ion in parentheses.
Example: potassium nitrate
Writing formulas of compounds
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Magnesium nitrate
Writing formulas of compounds
4.
If a Roman numeral appears after the name of the positive
element, this number indicates the oxidation number of
the positive element.
Example: tin (IV) chloride
Naming Binary Compounds
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State the name of the positive element first.
State the name of the negative element and change the
ending to -ide.
NaCl sodium chloride
CaS
_____________
Naming Binary Compounds
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If the positive element can have more than one positive
oxidation number use the stock system:
Stock System- Put a Roman numeral in parentheses after
the name of the positive element to show its oxidation
number.
Naming Binary Compounds
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CuCl2
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Note: Do not use the Stock System if only one positive
oxidation number is possible.
Naming Compounds that contain Polyatomic Ions
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Write the name of the positive element first.
If the positive element has more than one possible oxidation
number use the stock system.
The names and formulas of polyatomic ions are generally to
be memorized.
Examples
Greek Prefix System
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An older system of nomenclature is often used, especially for
compounds containing only nonmetals.
Greek prefixes are used to tell how many atoms are present
in the formula.