Chapter 18 Section 3

1. Chapter 18 Section 3 Writing formulas and naming compounds

2. Writing chemical formulas • Oxidation number is the number of electrons gained, lost, or shared by an elements atoms • Can be positive or negative • In ionic compounds the oxidation number is the same as the charge of the ion • Groups 1, 2, and 13-18 have set oxidation numbers for all elements in the group • Groups 3-12 have multiple oxidation numbers for the elements in the group • These oxidation numbers are written as roman numerals in the compound name

3. Writing chemical formulas (cont.) • Binary compounds contain only two elements • They always have a neutral charge • Determine the common multiple to get a zero charge for the compound

4. Writing the formula • First, write the symbol of the element that has the positive oxidation number, for ionic compounds that is the cation • Then write the symbol of the element that has the negative oxidation number, for ionic compounds that is the anion • Finally, find the least common multiple of the charges of each ion and determine the # of atoms of each element as a subscript of that element • Hint: the charge of one ion is the # of atoms of the other element

5. Practice • Write the practice problem formulas on page 567 #14-16 • Homework if not finished in class

6. Naming binary compounds • First, write the name of the positive ion (cation) • CaCl2 = calcium • Next determine the oxidation number for the positive ion • If the ion only has one possible oxidation number just write the ion name • If the ion has multiple oxidation numbers, determine the oxidation number, write the name of the ion and the oxidation # in parentheses as a roman numeral • CaCl2 = Calcium chloride • Fe2O3 = Iron (III) oxide

7. Naming binary compounds (cont.) • Then write the root of the negative ion (anion) • NaCl = sodium chlor… • Finally end the anion with the suffix –ide. • NaCl = sodium chloride • Practice problems # 17-19 page 568 • Homework if not finished in class

8. Compounds with complex ions • Polyatomic ion is an ion that contains multiple elements that act as a single ion • Can be positive or negative, although they are most commonly negative ions with ammonium being one of the only positive polyatomic ions

9. Writing formulas containing polyatomic ions • Follow the same rules as with binary compounds but when the polyatomic ion requires more than one ion, put parentheses around the entire ion and then add the subscript to indicate the number of ions required to balance the formula

10. Naming complex compounds • First, name the positive ion • NaCl = sodium chloride • NH4(NO3)= Ammonium nitrate • Then write the negative ion • NH4(NO3)= Ammonium nitrate = NH4++ NO3- • Practice naming the following complex compounds: • Na3PO4 • Al2(CO3)3 • CaCO3 • MgSO4

11. Naming binary covalent compounds • Binary covalent compounds are always formed between 2 nonmetal or metalloid elements • Use Greek prefixes to determine the number of atoms of each element in the formula • Mono = 1 • Di = 2 • Tri = 3 • Tetra = 4 • Penta = 5 • Hexa = 6 • Hepta = 7 • Octa = 8

12. Naming binary covalent compounds (cont.) • Disulfur Monoxide = S2O • Trinitrogenpentaoxide = N3O5 • If the first element only has one atom, just write the element name • Sulfur dioxide = SO2 • Carbon monoxide = CO

13. Compounds with water • Hydrates are compounds that have water attached to the atoms and written in the chemical formula • Common hydrates are cobalt chloride hexahydrate (CoCl2 H2O) and calcium sulfate dihydrate (CaSO4 H2O) • Anhydrous compounds are those that do not have water attached to the atoms but when exposed to water will form a hydrate • Anhydrous cobalt chloride (CoCl2) and anhydrous calcium sulfate (CaSO4)

14. Section review assessment • Page 571 • #20-23 • Homework if not finished in class • Lab tomorrow!