Ionic Compounds: Writing Type 1 Formulas

PolyAtomic Ions A molecule that is made up of 2 or more atoms that act as a unit and have an overall charge. Since the polyatomic ion acts as a unit, we treat them like we would a single element. How to recognize if the compound has a polyatomic ion: Count how many elements there are in the compound. If there are more than 2-you have a polyatomic ion and you can find it in the chart.

Writing Ionic (Type I) Formulas Using the Criss-Cross Method Steps: Write the cation (+) first followed by the anion (-). Mg Cl Determine the charges using the periodic table and write them as superscripts. Mg2+ Cl- Remember: the positive must equal negative! Drop the positive or negative sign and criss-cross the numbers to become new subscripts. Mg2 Cl1 Write the new formula with no charges and subscripts. MgCl2 Reduce when possible.

Examples: Colored Card Shuffle K and O Al and F Be and N Mg and S