6.4 - NOTES Naming and Writing Ionic Formulas

Ions and Ionic Compounds Atoms that have a charge; can be positive or negative Formed when an atom gains or loses electrons Metals tend to lose electrons to form positive ions  These ions are also called cations Nonmetals tend to gain electrons to form negative ions   These ions are also called anions

Polyatomic ions NH4+1 C2H3O2-1 An ion consisting of bonded atoms with a single charge Can be positive or negative They always stay together and can NEVER be split up Some examples are   NH4+1 C2H3O2-1

Ionic compounds Made of positive and negative ions The overall charge of an ionic compound is 0 (neutral)

Writing formulas The cation (metal) is first, then the anion (non-metal). The total charge must be zero, so we use subscripts to indicate the number of ions. The ions must have the smallest ratio possible.

Examples Sodium and bromine Na+1 Br-1 NaBr calcium and fluorine Ca+2 F-1 CaF2

Potassium and oxygen K+1 O-2 K2O barium and sulfur Ba+2 S-2 BaS

Aluminum and chlorine Al+3 Cl-1 AlCl3 magnesium and nitrogen Mg+2 N-3 Mg3N2

Naming Compounds Monatomic cations are known by their name. For example, Na+ is sodium Monatomic anions have the ending “ide,” which means negative. For example, O-2 is known as oxide. Polyatomic ions have their normal names.

Examples RbNO2 Rubidium Nitrite CuSO4 Copper (II) Sulfate

Writing formulas from names Using the given names, the cation comes first and the anion comes second. Remember the ending –ide usually means it is a single element, while the endings –ite and –ate indicate a polyatomic ion Some metals have multiple charges, like copper and gold. To indicate the difference in the charge on the ions, Roman numerals are used to indicate the form of the ion present in the formula. Gold (III) chloride vs. gold (I) chloride   Au+3 Cl-1  AuCl3 Au+1 Cl-1  AuCl

Ca(HSO4)2 Calcium Bisulfate Calcium Hydrogen Sulfate (NH4)3PO4 Ammonium Phosphate

Al2(SO3)3 Aluminum Sulfite Ag(CO3)2 Silver Carbonate