1. 22.3 – Writing formulas for Ionic Compounds Part A Focus on what is in PINK

2. Objectives Write formulas for ionic compounds

3. Writing Ionic Formulas Watch the Tyler DeWitt Video and complete the viewing guide, you will add it to your notes on this chapter Youtube video Youtube video

4. Binary Ionic Compounds A compound composed of 2 elements To write a chemical formula for a binary compound, you need to know: which elements are involved how many electrons they lose or gain to become stable

5. Ionic Compounds are NEUTRAL Although the individual ions in a compound carry charges, the compound itself is neutral A formula must have the right number of positive ions and the right number of negative ions so the charges balance

6. Oxidation Number The number of electrons an atom must gain, lose or share to become stable  Cations = lose electrons  Anions = gain electrons

7. Oxidation Number Determined by which group the element is in and how many valence electrons it has Valence electrons = The BONDING electrons found in the outermost energy level

8. Oxidation Number Group 1 = 1 valence electron  Loses 1 e- to become stable  Ion = +1 charge Group 2 = 2 valence electron  Loses 2 e- to become stable  Ion = +2 charge Group 3 = 3 valence electron  Loses 3 e- to become stable  Ion = +3 charge

9. Oxidation Number Groups 3-12 = Transition metals = variable # of electrons, unpredictable charges Group 13 = 3 valence electron  Loses 3 e- to become stable  Ion = +3 charge

10. Oxidation Number Group 14 = 4 valence electron  Can gain or lose 4e- to become stable  Ion = ±4 charge Group 15 = 5 valence electron  Gains 3e- to become stable  Ion = -3 charge Group 16 = 6 valence electron  Gains 2e- to become stable  Ion = -2 charge

11. Oxidation Number Group 17 = 7 valence electron  Gains 1e- to become stable  Ion = -1 charge Group 18 = *8 valence electron  STABLE  No charge, no ions

12. Oxidation #/Charges of Ions

13. Write Formulas for these ions Potassium ion Magnesium ion Oxide (oxygen) ion K+ Mg 2+ O 2-

14. Transition Elements Can have multiple oxidation numbers Express using Roman numerals For example, the oxidation number of iron in iron (III) oxide is 3+.

15. Write Formulas for these ions Copper (I) ion Chromium (VI) ion Mercury (II) ion Cu 1+ Cr 6+ Hg 2+

16. Step By Step – Writing Formulas 1. Write the symbol of the element with the positive oxidation number or charge 2. Write the symbol of the element with the negative oxidation number or charge 3. The charge (without the sign) of one ion becomes the subscript of the other ion. Reduce the subscripts to the smallest whole numbers that retain the ratio of ions.

17. Criss-Cross Method

18. Writing Formulas Write the formula for calcium chloride.  Calcium is Ca +2  Chloride is Cl -1 Ca +2 Cl -1 Cl -1 CaCl 2

19. In-Class Assignment/Homework PS 22.3 A WKT 1 - Criss Cross practice