chemical formulas. chemical formulas a chemical formula provides the clearest and simplest method...

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.