Writing Formulas for Ionic Compounds

1. Writing Formulas for Ionic Compounds

2. Oxidation Numbers for the Group A Elements 3+ 1+ 2+ 1- 0 3- 2- NA

3. When you write ions, use the element symbol and the oxidation number written as a superscript. bromine sulfur cesium called bromide in a compound Br-1 called sulfide in a compound S-2 Anions change end of name to –ide. Cs+1

4. If you need the oxidation number for a transition or inner transition metal, it will be given to you because these elements typically have more than one oxidation number. • Ox. # for transition/inner transition metals will be in the form of a Roman Numeral! • Exceptions: • Pb and Sn use Roman numerals even though they are NOT transition metals • Ag and Zn do NOT use Roman Numerals even though they ARE transition metals

5. example: • nickel (II) chloride (NiCl2) The (II) belongs to nickel which means nickel has a +2 charge while chlorine has a -1 charge!

6. What is the oxidation number for the metal in each compound? • Lead (IV) oxide • Scandium (II) nitride Pb+4 Sc+2

7. Monatomic Ions • A monatomic ion is an ion made up of one element. • examples: H+1 O-2 F-1 Ba+2 • Monatomic ions bond to make a binary compound. • Binary compounds are made of a monatomic cation and a monatomic anion.

8. To Write Formulas with Monatomic Ions, use the criss-cross method! bromine: name changed to bromide in a compound Write the formula for barium bromide. • First: Write each element symbol and oxidation number. ***Always write the positive ion first!!! • Next: Criss-cross the oxidation numbers. Swap the ox. #’s and write them as SUBSCRIPTS (lose the + and – signs) Ba+2 Br-1 Ba+2 Br-1 Ba1Br 1 = BaBr2 2

9. Write the formulas for: • Iron (III) chloride • Sodium oxide • Magnesium nitride

10. Polyatomic Ions • A polyatomic ion is an ion made up of more than one element. • These are on the back of your periodic table! • The entire polyatomic ion has an oxidation number (NOT the individual elements).

11. Polyatomic Ions Example: PO4-3 is the polyatomic ion phosphate with an oxidation number of -3. Example: SO3-2 is the polyatomic ion sulfite with an oxidation number of -2. • Most polyatomic ions end in the suffix –ate or –ite.

12. To write formulas with polyatomic ions: • First: Write each element and polyatomic ion symbol and oxidation number. ***Always write the positive ion first!!! • Next: Place polyatomic ion in PARANTHESES • Finally: criss cross the oxidation numbers • NEVER, NEVER, NEVER, EVER CHANGE THE SUBSCRIPT WITHIN THE POLYATOMIC ION ITSELF!

13. Write formulas for: • Calcium Phosphate • Magnesium Nitrate:

14. ONE LAST NOTE: Chemical formulas must be in the lowest, reduced form!!! Write formulas for: • lead (II) oxide • calcium sulfide

15. Let’s Try More!

16. Nomenclature of Ionic Compounds • Nomenclature means naming. Naming Ionic Compounds with Monatomic Ions • First: Name the cation (positive ion) – DO NOT CHANGE THE CATION’S NAME IN ANY WAY and write it down. • Note: If the cation is a transition or inner transition metal, you must indicate its charge (the oxidation number) using Roman numerals in parentheses after the metal’s name. • Ex: iron (II) chloride; its chemical formula is: FeCl2

17. Ex: What would these anions be named in a compound? • Oxygen ______________ • Sulfur ______________ • Nitrogen ______________ • Iodine ______________ • Phosphorus ______________ • Chlorine ______________

18. Name These: Ex: NaCl ____________________ Pb3P2 ___________________

19. Naming Ionic Compounds with Polyatomic Ions • First: Name the cation ion first (NEVER CHANGE THE CATION’S NAME). • Note: If the cation is a transition or inner transition metal, you must indicate its charge using Roman Numerals in parentheses after the metal’s name. Ex: iron (II) hydroxide (its chemical formula is Fe(OH)2) • Next: Name the polyatomic ion – ON THE BACK OF THE PT – (NEVER CHANGE THE POLYATOMIC’S NAME). • HINT: Polyatomic ions usually end in –ate or –ite!

20. Try These: • Li2SO4 • (NH4)2O

21. I will do the rest with you on the board!