Criss CrossChargeEmpirical Formula OBJECTIVE Too calculate the SUBSCRIPT

Criss Cross-Charge-Empirical Formula • OBJECTIVE: Too calculate the SUBSCRIPT MOLE RATIO of an ionic BINARY compound, GIVEN two elements in a compound. • WHAT YOU NEED: OXIDATION STATE( charges) from periodic table. • WHAT YOU MUST KNOW: the charges of the groups – – Group 1 is 1+ Group 2 is 2+ Group 17 is 1 - (in binary compounds, can vary in others. ) Group 16 is 2 - (in binary, some exceptions not needed here) SKILL: the criss cross method. STEP#1: write the formula with charges for both atoms. STEP#2: the charge of one element becomes the subscript of the other, use absolute values of the charges. STEP#3: Reduce the subscripts to whole number integers (reduce them to lowest terms – empirical formula)

EXAMPLE: Mg and Cl • STEP ONE: Cl is in group 17 and is 1 - in binary compounds. Mg is in group 2 and is always 2+ in all compounds. • STEP TWO: write formula with charges Mg 2+ Cl 1 • STEP THREE: cross the absolute values of charges as subscript of the other element. Mg 2+ NOTE: the subscript Cl 1 - of 1 for Mg is understood as in algebra. • STEP THREE continued Mg 1 Cl 2 Mg. Cl 2

EXAMPLE: Na and O • STEP ONE: Na is in group 1 and is 1+ in binary compounds. O is in group 16 and is always 2 - in all compounds(for now!). • STEP TWO: write formula with charges Na 1+ O 2 • STEP THREE: cross the absolute values of charges as subscript of the other element. Na 1+ O 2 - • STEP THREE continued Na 2 O 1 NOTE: the subscript ALWAYS WRITE CATION(+ ) FIRST of 1 for O is understood as in algebra. Na 2 O