Naming Compounds and Writing Formulas for Ionic Compounds Chapter 9 Section 2

Naming Binary Ionic Compounds Composed of two elements Cation name followed by anion name NaF CaCl2 Li3N Sodium fluoride Calcium chloride Lithium nitride

Naming Binary ionic compounds with transition metals Recall transition metal ions have multiple charges First start with ion that only has one possible charge “position of strength” Then determine transition metal ionic charge. Example: CuO Copper and oxygen Copper can be +1 or +2… …but Oxygen is always -2. Position of strength! 1:1 ratio means this copper must be +2 to cancel out the -2 of the oxygen atom. Copper (II) oxide

You try it! SnS2 FeCl3 SnF2 CuI2 CoI2 CuI Tin (IV) sulfide Iron (III) chloride Tin (II) fluoride Copper (II) iodide Cobalt (II) iodide Copper (I) iodide

Writing Formulas for Binary Ionic Compounds Write the symbol for the cation followed by the symbol for the anion. Add whatever subscripts are needed to balance the charges. Potassium chloride Calcium bromide

A little trickier… Iron (III) oxide How do you balance this? Iron (III) is Fe3+ Oxide is O2- How do you balance this? Crisscross method, or finding the least common multiple method.

Iron (III) Oxide (Rust) LCM Method 3x2 = 6 (least common multiple) Two Fe3+ cations have a net charge of: +6 Three O2- anions have a net charge of: -6 Balanced formula for Iron(III) Oxide is Fe2 O3

Crisscross Method Numerical charge of each ion is crossed over and used as a subscript for the other ion The signs of the numbers are dropped. Fe3+ O2- Fe2O3 2(3+) + 3(2-) = 0

Crisscross doesn’t always work… Calcium Sulfide Ca2+ S2- Ca2 S2 Remember: formulas for ionic compounds show the lowest whole-number ratios of ions The correct formula for Calcium sulfide is CaS 1(2+) + 1(2-) = 0 Crisscross method unnecessary in this case

Ternary Ionic Compounds Ternary Compound: A compound that contains atoms of 3 different elements Most ternary ionic compounds contain a polyatomic ion THIS IS WHY YOU NEED TO HAVE THEM MEMORIZED!!! You need to recognize polyatomic ions quickly

Example: write the formula from the name How would you write the formula for calcium nitrate? Write the formula (symbol and charge) for each ion Balance the charges (hint: use crisscross here) Ca2+ and NO3- Ca(NO3 )2 Include parenthesis around the polyatomic ion followed by the subscript of how many of those ions are needed to balance the charge of the compound

More examples If you only need one of the polyatomic ions to balance the charge of the compound, you do not need to use parentheses Calcium Carbonate Ca2+ and CO32- CaCO3 No parentheses Strontium Sulfate Sr2+ and SO42- SrSO4 Lithium Carbonate Li+ and CO32- Li2 CO3

Write the formulas for the following Potassium Sulfate K+ and SO42- K2 SO4 Magnesium Hydroxide Mg2+ and OH- Mg(OH)2

Naming Ternary Ionic Compounds Name the cation first, followed by the anion Determine the charge of the polyatomic ion. Balance the polyatomic anion by adding an appropriate subscript for the cation. K2Cr2O7 Composed of K+ and Cr2O7-2 potassium dichromate

Name the following Compounds LiCN Lithium Cyanide Sr(H2PO4 )2 Strontium dihydrogen phosphate (NH4 )2 C2O4 Ammonium Oxalate Fe(ClO3)3 Iron (III) Chlorate