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Criss Cross-Charge-Empirical Formula

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+

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Criss Cross-Charge-Empirical Formula

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  1. Criss Cross-Charge-Empirical Formula • OBJECTIVE: Too calculate the SUBSCRIPT MOLERATIO 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)

  2. 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 • STEP THREE: cross the absolute values of charges as subscript of the other element. • STEP THREE continued Mg2+Cl1- Mg2+Cl1- NOTE: the subscript of 1 for Mg is understood as in algebra. Mg1Cl2 MgCl2 

  3. 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 • STEP THREE: cross the absolute values of charges as subscript of the other element. • STEP THREE continued Na1+O2- ALWAYS WRITE CATION(+) FIRST Na1+O2- NOTE: the subscript of 1for O is understood as in algebra. Na2O1 Na2O 

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