Ionic Compounds: Naming and Formula Writing

Naming Compounds Chemists have developed systematic ways to name compounds. If you learn the naming rules, you can examine a compound’s formula and determine its name, and vice versa. Many compounds also have a common name. NaCl has the common name salt and the systematic name sodium chloride.

Oxidation Numbers All compounds have an electrical charge of zero (they are neutral). An oxidation number indicates the charge on the atom (or ion) when electrons are lost, gained, or shared in chemical bonds.

Naming Ionic Compounds Identify if the metal cation has more than one potential charge. Such metals are usually (but not always) found in the transition metals section of the periodic table. Notable Exceptions: Always Zn2+ and Ag+ Sn and Pb can have multiple charges

IONIC COMPOUNDS If charges cancel, just write the symbols Na+1 Cl-1 NaCl If charges do not cancel, criss-cross: Ca+2 Cl-1 CaCl2 ***Do not move the charge, only the number ***Do not write the 1

Binary Ionic Compounds Binary compounds are those that contain only two different elements. The names for binary ionic compounds containing a metal that forms only one type of ion have the following form: Name of Cation + Base Name of Anion + ide

Binary Ionic Compounds Since the charge of the metal is always the same for these types of compounds, it need not be specified in the compound’s name. Example: MgF2 Cation Name: Magnesium Anion Name: Fluorine Correct Anion Name: Fluoride Complete Name: Magnesium Fluoride

Binary Ionic Compounds

Practice Name these compounds: CaO Al2O3 KF MgCl2 Li3N Calcium Oxide Aluminum Oxide KF Potassium Fluoride MgCl2 Magnesium Chloride Li3N Lithium Nitride

Practice Write the formula for these ionic compounds: Potassium bromide KBr Sodium oxide Na2O Zinc nitride Zn3N2

Binary Ionic Compounds If the cation could have more than one charge, then the charge must be specified in the metal’s name. We specify the charge with a Roman numeral (in parentheses) following the name of the metal.

Binary Ionic Compounds For example, we distinguish between Cu+ and Cu2+ by writing a (I) to indicate the 1+ ion or a (II) to indicate the 2+ ion: Cu+ Copper(I) Cu2+ Copper(II)

Binary Ionic Compounds These compounds are named using the following form: Name of Cation (charge of metal in roman numerals) Base Name of Anion + ide + +

Binary Ionic Compounds We can determine the charge of the metal from the chemical formula of the compound. The sum of all the charges must be zero.

Binary Ionic Compounds What is the charge of iron in FeCl3? +3 How do we know? Chlorine has a -1 charge and there are 3 of them What is the name for FeCl3? Iron (III) Chloride

Practice Name the following compounds: PbCl4 Lead (IV) Chloride PbO Lead (II) Oxide Explain why CaO is not named calcium (II) oxide. Calcium has a +2 charge and oxygen has a -2 charge, so the charges already balance

Practice Write the formula for the following compounds: Chromium (II) chloride CrCl2 Tin (IV) oxide SnO2 Iron (III) oxide Fe2O3

Writing Formulas a Little Quicker Simply cross the oxidation numbers and make them positive

Let’s try some more! Manganese (IV) Phosphide Manganese (IV) Oxide Mn4+ + P3-  Mn3P4 Manganese (IV) Oxide Mn4+ + O2-  Mn2O4  MnO2

Polyatomic Ionic Compounds Ionic compounds containing polyatomic ions are named using the same procedure we apply to other ionic compounds, except that we use the name of the polyatomic ion whenever it occurs.

Polyatomic Ionic Compounds For example, we name KNO3 using its cation, K+, potassium, and its polyatomic anion, NO3-, nitrate. KNO3 potassium nitrate

Remember the Polyatomic Ions NO31- Nitrate SO42- Sulfate PO43- Phosphate OH1- Hydroxide CO32- Carbonate NH41+ Ammonium What types of bonds occur in polyatomic ions?

Practice Fe(OH)2 Iron Hydroxide NH4NO3 Ammonium Nitrate

Practice Write the formula for the following compounds: barium nitrate Ba(NO3)2 ammonium iodide NH4I iron (III) hydroxide Fe(OH)3

Polyatomic Ionic Compounds Many polyatomic ions are oxyanions, anions containing oxygen. When a series of oxyanions contain different numbers of oxygen atoms, they are named systematically according to the number of oxygen atoms in the ion.

Polyatomic Ionic Compounds If there are two ions in the series, the one with more oxygen atoms is given the ending -ate and the one with fewer is given the ending -ite. NO3− nitrate SO42− sulfate NO2− nitrite SO32− sulfite

Polyatomic Ionic Compounds If there are more than two ions in the series, then the prefixes hypo-, meaning “less than,” and per-, meaning “more than,” are used. ClO − hypochlorite BrO − hypobromite ClO2− chlorite BrO2− bromite ClO3− chlorate BrO3− bromate ClO4− perchlorate BrO4−perbromate

Practice K2CrO4 Potassium Chromate Mn(NO3)2 Manganese Nitrate

Practice Write the formula for the following compounds: sodium perchlorate NaClO4 sodium chlorite NaClO2 sodium nitrate NaNO3 sodium nitrite NaNO2