Writing formulas for binary ionic compounds
- Binary compounds- composed of 2 elements
- Cross method – the numerical charge of each ion is crossed over and used as a subscript for the other ion.
- Ex) Ca 2+ S2- → Ca2S2 → CaS
- Keep in mind, the charges are written as superscripts and the values in the compound are written as subscripts, could not format it correctly.
- This compound is called Calcium Sulfide
- Remember formulas for ionic compounds show the lowest, whole number ratio of the ions.
Writing formulas for ternary ionic compounds
- Ternary compounds- contain atoms of 3 different elements (usually polyatomic ion)
- Same method using charge of polyatomic ion
- Use parentheses around every polyatomic ion
- Ex) Ca2+ (CO3 2-) → Ca2(CO3)2 → CaCO3
- This compound is called Calcium Carbonate
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