Writing Chemical Formulas

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Presentation Description

Guidelines for writing binary and ternary ionic compounds

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Writing Chemical Formulas: 

Writing Chemical Formulas Formulas must be electrically balanced Neutral compounds Total Positive charge = Total Negative charge Add the charges algebraically H 2 O 2(+1) + (-2) = 0

Practice Writing Formulas: 

Practice Writing Formulas Magnesium & Iodine Zinc & Sulfur Cobalt & Fluorine Aluminum & Oxygen MgI 2 ZnS CoF 2 Al 2 O 3 Pause the Presentation and complete the remaining examples

Criss-Cross Method: 

Criss-Cross Method Write the positive ion first, then the negative ion Write each respective oxidation number above the ion Cross the oxidation numbers i.e. – the oxidation number of the positive ion becomes the subscript of the negative ion, and vice versa (don’t keep the + and – signs)

Practice Formulas: 

Practice Formulas Calcium & Chlorine Aluminum & Oxygen +2 Cl -1 Ca 2 +3 O -2 Al 3 2

More Practice Writing Formulas: 

More Practice Writing Formulas Calcium & Oxygen Sodium & Sulfur Chromium & Chlorine Silver & Iodine CaO Na 2 S CrCl 3 AgI Pause the Presentation and complete the remaining examples

Writing formulas with multivalent ions: 

Writing formulas with multivalent ions Some metals (typically transition metals) have more than one oxidation number Oxidation number is denoted with Roman numerals in parentheses after the name of the positive ion Use the charge given in parentheses; no need to look it up

More Practice Writing Formulas: 

More Practice Writing Formulas Iron (III) & Oxygen Tin (IV) & Sulfur Lead (II) & Chlorine Copper (I) & Iodine Fe 2 O 3 SnS 2 PbCl 2 CuI Pause the Presentation and complete the remaining examples

Polyatomic Ions: 

Polyatomic Ions Polyatomic ion – an ion that has two or more different elements Treat it as if it acts as a single particle If (after the “cris-cross”) the subscript for the entire polyatomic ion is 2 or more , you must surround the formula for the polyatomic ion in parentheses ( ) Do not change the subscripts of the polyatomic ion itself!!!

Practice Writing Formulas (Polyatomic ions): 

Practice Writing Formulas (Polyatomic ions) Lithium & Carbonate Copper (II) & Nitrate Sodium & Chromate Strontium & Thiosulfate Lead (IV) & Sulfate Li 2 CO 3 Cu(NO 3 ) 2 Na 2 CrO 4 SrS 2 O 3 Pb (SO 4 ) 2 Pause the Presentation and complete the remaining examples