Naming Compounds and Molecules

1. Naming Compounds and Molecules

2. The FIRST thing you must do is decide if the compound is IONIC or COVALENT. • Why? Each type of compound is named differently!

3. Follow the prefix method Affix the following prefixes to each element indicating how many there are. One Mono- Two Di- Three Tri- Four Tetra- Five Penta- Six Hexa- Seven Hepta- Eight Octa- Nine Nona- Ten Deca- If it is Covalent…

4. Other Covalent Rules • Name the element farther left on the periodic table first. • If the first element only has one atom, the “mono-” is dropped. • On the last word, the suffix is dropped and the ending –ide is added.

5. Covalent Examples • CO2 • There is only one carbon, so the “mono-” is dropped. • There are two oxygen atoms = Di Carbon Dioxide • CO • There is only one carbon, so the “mono-” is dropped. • There is one oxygen atom = mono Carbon Monoxide

6. A few more Covalent Examples • Tetracarbon Difluoride • There are four carbon atoms • There are two fluorine atoms C4F2 • Dihydrogen Monoxide • There are two hydrogens • There is one oxygen H2O

7. That was easy, Right? Let’s try ionic compounds…

8. If it is Ionic… • Ionic compounds DO NOT have prefixes. • Example: Write the formula for Aluminum Fluoride • How do you do it??? • Let’s think about it practically, first. • How? Draw the Bohr model for each and figure out how many of each atom are needed.

9. Another Way to Think about It… • Aluminum needs to give 3 electrons away. • Fluorine only needs one electron • You need 3 fluorines to take all of aluminum’s electrons AlF3

10. That Seems Like A lot of work. Is There Another Way to Think About It??? • YES!!! • Step 1: Determine the Charge of the ion. • How? What would its charge be if its outer energy level were full? • First, write the element’s symbol and then its charge as a superscript • Example: Aluminum Fluoride

11. Aluminum • How many valence electrons does Aluminum have? 3 • What will Aluminum do with these? Give them away. 13+ (protons) 10- (electrons) 3+ (total charge) Al+3

12. What about Fluorine? • How many valence electrons does fluorine have? 7 • What does fluorine need to be like a noble gas? One more electron 9+ (protons) 10- (electrons) -1 (total charge) F-1

13. A positive ion is called a CATION. • A negative ion is called an ANION. • The metal is always listed first, the nonmetal second. • The ending of the nonmetal is dropped and the ending –ide is added.

14. Now What? • Step 2: Write each symbol and charge– write the metal first, the nonmetal second Al F • Step 3: Follow the Criss-Cross Rule • Aluminum’s charge becomes fluorine's subscript and vice versa • The charge symbols are dropped (the + or -) +3 -1

15. Final Formula AlF3

16. Another Example: Sodium Oxide • Step 1: Find the charges of the ions • Sodium has 1 valence electron • It gives the electron away • Charge is +1 • Oxygen has 6 valence electrons • It needs two more electrons • Charge is –2 Na+1 O-2

17. Step 2: Write each symbol and charge NaO Step 3: Follow the Criss-Cross Rule -2 +1

18. Final Formula for Sodium Oxide Na2O

19. Another Way to Think About It: Using Lewis Dot Structures • Draw the Lewis Dot for each element • Sodium only has one electron to give. • In order for oxygen to be like a noble gas, there must be two sodiums. Na2O Na O Na

20. Name the Following Ionic Compounds • BaBr • Remember, NO PREFIXES NEEDED!! • Barium Bromide • K3P • Potassium Phosphide • Rb2S • Rubidium Sulfide

21. Transition Metals • Transition metals can often make more than one ion. • The ion charge is written as a ROMAN NUMERAL after the metal • The charges of metals are ALWAYS positive. • Examples: • Iron (III) Fe+3 • Copper (II) Cu+2 • Remember, when naming ionic compounds, if it is a transition metal, to include the roman numeral!

22. Example with a Transition Metal • Copper (II) Chloride • Step 1: Find the charges of the ions • We already know copper’s charge from the roman numeral (remember, metals always have a POSITIVE charge) Cu+2 • Chlorine has 7 valence electrons • Chlorine needs 1 electron • Charge is –1 Cl-1

23. Step 2: Write the Symbols & Charges Cu Cl Step 3: Follow the Criss-Cross Rule -1 +2

24. Final Formula for Copper (II) Chloride: CuCl2

25. Another way to Think About it Using Lewis Dot Structures Final Answer: CuCl2 • First, draw the Lewis Dot for each element. • Copper gives away two electrons • Chlorine needs one electron • It takes 2 chlorines to take all of copper’s electrons. Cl Cu Cl

26. If it is Polyatomic… • You will recognize a polyatomic (in most cases) by the ending of the last word in the name. • Many polyatomics DO NOT end in –ide • Examples: Sulfate, Nitrite, Carbonate • Examples that end in –ide: Hydroxide, Cyanide • Polyatomics already give you the charge of the ion (just look it up on a chart) • Write the metal first, the polyatomic second, then follow the rules of ionic bonding. • If more than one polyatomic is needed, put the entire polyatomic in parentheses and put the subscript outside the parentheses.

27. Polyatomic Example • Lithium Sulfate • Step 1: Find the charges of the ions • Lithium has 1 valence electron. • Lithium gives the electron away = +1 charge Li+1 • Sulfate…look it up on a chart SO4-2

28. Step 2: Write the Symbols & Charges Li SO4 Step 3: Follow the Criss-Cross Rule -2 +1

29. Final Formula for Lithium Sulfate Li2(SO4)1

30. OK, time for more practice. See the practice sheet…. 