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Learn about ions, polyatomic ions, and ionic compounds. Understand the rules for writing formulas and naming compounds. Also, explore the application of pure and impure water.
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B.9 Ions and Ionic Compounds • Ions • 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 • 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-2BaS
Aluminum and chlorine • Al+3Cl-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 Nitrate • CuSO4 • Copper Sulfate
Fe(HSO4)2 • Iron Bisulfate • (NH4)3PO4 • Ammonium Phosphate
Al2(SO3)3 • Aluminum Sulfite • Pb(CO3)2 • Lead Carbonate
FeCl3 • Iron Chloride • SnI4 • Tin Iodide
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 –iteand –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
B.12 APPLICATION: Pure and Impure Water • Why is it useless to get water that is 100% pure? • Very expensive • It’s hard to remove trace amounts of metals and other ions from water