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CHEMICAL FORMULAS
Chemical Formulas 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 AlCl3 NaCl MgO CO2
LiH
General Rules for Oxidation Numbers1. Charge on pure elements is _______.2. All metals of Group IA are ________.3. All metals of Group IIA are _______.4. The charge on all elements in Group
IIIA is _____ except Tl which can also be ____.
5. The charge on hydrogen is ___or __.6. The charge on fluorine is ____.
General Rules for Oxidation Numbers7. 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 Ammonium_______ Cyanide_________ Acetate__________ Carbonate_______ Nitrate__________
Sulfate__________ Hydroxide_______
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 Examples: Oxide = ________ telluride =
________ Chloride = ______ hydride =
________ __________ = S2- __________ = P3-
Writing Formulas of Compounds2. Use subscripts to make the formula
contain the number of atoms required for a neutral formula unit.
Example: sodium chlorideNa1+Cl1-
1+1- = 0NaCl
Writing Formulas of Compounds calcium chloride sodium oxide
Writing formulas of compounds 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 Magnesium nitrate
Writing formulas of compounds4. 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 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 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 CuCl2
Note: Do not use the Stock System if only one positive oxidation number is possible.
Naming Compounds that contain Polyatomic Ions 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 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.