2. Chemical Formulas Chemistry Dr. May

3. Valence Electrons Sum of the outermost s an p electrons Na = 1 Ca = 2 Al = 3 C = 4 N = 5 O = 6 Cl = 7 Ne = 8

4. Oxidation Number Number of electrons lost (+) or gained (–) during a chemical reaction Na = +1 Ca = +2 Al = +3 C = +4 or –4 N = +5 or –3 O = –2 Cl = –1 Ne = 0

5. NaCl Valence Electrons Na has one valence electron 1s 2 2s 2 2p 6 3s 1 Cl has seven valence electrons 1s 2 2s 2 2p 6 3s 2 3p 5

6. NaCl Ions Na transfers its electron to Cl to become the Na +1 ion which has eight valence electrons 1s 2 2s 2 2p 6 3s 1  1s 2 2s 2 2p 6 Cl accepts the electron to become the Cl –1 ion which has eight valence electrons 1s 2 2s 2 2p 6 3s 2 3p 5  1s 2 2s 2 2p 6 3s 2 3p 6

7. Chemical Formulas - NaCl Sodium has an oxidation number of +1 Chlorine has an oxidation number of –1 One Na +1 combines with one Cl –1 One negative cancels one positive NaCl is a neutral ionic compound

8. CaCl 2 Valence Electrons Ca has two valence electron 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 Cl has seven valence electrons 1s 2 2s 2 2p 6 3s 2 3p 5

9. CaCl 2 Ions Ca transfers its two electrons to two atoms of Cl to become the Ca +2 ion which has eight valence electrons 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2   1s 2 2s 2 2p 6 3s 2 3p 6 Two Cl atoms accept the two electrons to become two Cl –1 ions which have eight valence electrons #1 Cl –1 1s 2 2s 2 2p 6 3s 2 3p 5  1s 2 2s 2 2p 6 3s 2 3p 6 #2 Cl –1 1s 2 2s 2 2p 6 3s 2 3p 5  1s 2 2s 2 2p 6 3s 2 3p 6

10. Chemical Formulas – CaCl 2 Calcium has an oxidation number of +2 Chloride has an oxidation number of –1 One Ca +2 combines with two Cl –1 Two negatives cancel two positives CaCl 2 is a neutral ionic compound

11. Na 2 O Valence Electrons Na has one valence electron 1s 2 2s 2 2p 6 3s 1 O has six valence electrons 1s 2 2s 2 2p 4

12. Na 2 O Ions Two atoms of Na transfer two electrons to one atom of O to become two Na +1 ions each having eight valence electrons #1 Na +1 1s 2 2s 2 2p 6 3s 1  1s 2 2s 2 2p 6 #2 Na +1 1s 2 2s 2 2p 6 3s 1  1s 2 2s 2 2p 6 O accepts the two electron to become the O –2 ion which has eight valence electrons 1s 2 2s 2 2p 4   1s 2 2s 2 2p 6

13. Chemical Formulas – Na 2 O Sodium has an oxidation number of +1 Oxygen has an oxidation number of –2 Two Na +1 combine with one O –2 Two negatives cancel two positives Na 2 O is a neutral ionic compound

14. Write Formulas Na +1 and Br –1 Na +1 and O –2 Ca +2 and Br –1 Ca +2 and O –2 Al +3 and Br –1 Al +3 and O –2 Fe +3 and Br –1 NaBr Na 2 O CaBr 2 CaO AlBr 3 Al 2 O 3 FeBr 3

15. Six Polyatomic Ions OH –1 – Hydroxide SO 4 –2 – Sulfate CO 3 –2 – Carbonate NO 3 –1 – Nitrate PO 4 –3 – Phosphate NH 4 +1 – Ammonium

16. Chemical Formulas – NaNO 3 Sodium has an oxidation number of +1 Nitrate has an oxidation number of –1 One Na +1 combines with one NO 3 –1 One negative cancels one positive NaNO 3 is a neutral ionic compound

17. Chemical Formulas – Na 2 SO 4 Sodium has an oxidation number of +1 Sulfate has an oxidation number of –2 Two Na +1 combine with one SO 4 –2 Two negatives cancel two positives Na 2 SO 4 is a neutral ionic compound

18. Chemical Formulas – Al(OH) 3 Aluminum has an oxidation number of +3 Hydroxide has an oxidation number of –1 One Al +3 combines with three OH –1 Three negatives cancel three positives Al(OH) 3 is a neutral ionic compound

19. Chemical Formulas – Ca 3 (PO 4 ) 2 Calcium has an oxidation number of +2 Phosphate has an oxidation number of –3 Three Ca +2 combines with two PO 4 –3 Six negatives cancel six positives Ca 3 (PO 4 ) 2 is a neutral ionic compound

20. Write Formulas Na +1 and NO 3 –1 Na +1 and SO 4 –2 Ca +2 and NO 3 –1 Ca +2 and SO 4 –2 Al +3 and NO 3 –1 Al +3 and SO 4 –2 Fe +3 and OH –1 NaNO 3 Na 2 SO 4 Ca(NO 3 ) 2 CaSO 4 Al(NO 3 ) 3 Al 2 (SO 4 ) 3 Fe(OH) 3

21. Write Formulas NH 4 +1 and NO 3 –1 NH 4 +1 and SO 4 –2 Ca +2 and CO 3 –2 Ca +2 and PO 4 –3 Al +3 and OH –1 Al +3 and PO 4 –3 NH 4 +1 and OH –1 NH 4 NO 3 (NH 4 ) 2 SO 4 CaCO 3 Ca 3 (PO 4 ) 2 Al(OH) 3 AlPO 4 NH 4 OH

22. The End This presentation was created for the benefit of our students by the Science Department at Howard High School of Technology Please send suggestions and comments to rmay@nccvt.k12.de.us