1. Science 10 Unit 2

2. In an ionic compound, positive charges must balance the negative charges.  e.g.: What is the formula for magnesium phosphide? Magnesium is Mg 2+ Phosphorous is P 3- Lowest common multiple of 2 and 3 is 6 3 Mg 2+ ions and 2 P 3– ions Mg 3 P 2

3.  e.g.: What is the formula for calcium oxide? Calcium is Ca 2+ Oxygen is O 2- 1 Ca 2+ ion and 1 O 2– ion CaO (remember, the subscript 1 is never written) Mg 2+ P 3- Mg 2+ P 3- Mg 2+ 6+6- Mg 3 P 2

4. 1. Write both symbols (+ion first) with ion charge 2. Criss-cross the charges and write them as subscripts 3. Reduce if possible MgO 2+2- (remember, the subscript 1 is never written) Mg O 22 Only use if you understand that the + and - charges must balance! Magnesium oxide

5.  Sometimes, metal ions have more than one combining capacity FeO 2+2- FeO e.g.Cu 2+ Cu 1+ Fe 3+ Fe 2+ The name of the compound will include a roman numeral that tells you which combining capacity to use Iron II oxidee.g.Iron III oxide FeO 3+2- Fe 2 O 3 1+I 2+II 3+III 4+IV 5+V 6+VI 7+VII

6. 1. Write the name of the metal first. 2. Write the name of the non-metal second, and change the ending to “-ide” 3. ONLY IF THE METAL HAS 2 OR MORE ION CHARGES, Include a roman numeral to indicate which one it is. e.g.NaCl MgF 2 CuCl 2 Sodiumchloride Magnesiumfluoride copper has 2 ions: Cu 1+ Cu 2+ which one is it?

7. To find out which copper ion it is, look at the charge on the anion and balance the charges in reverse. CuCl therefore must be copper I chloride CuCl 2+1- CuCl 2 Therefore it is copper II chloride from periodic table Cl 1- 2-

8. Some groups of atoms act as individual ions e.g.SO 4 -2 Sulphate ion-2 OH -1 Hydroxide ion-1 PO 4 -3 Phosphate ion-3 When writing formulas and naming, pretend the polyatomic ion is just one atom and follow the rules as usual. e.g. K +1-3 K 3 PO 4 Potassium phosphate Don’t change the endings of polyatomic ions Ion Charge PO 4

9. Aluminum sulphate Copper (II) sulphate AlSO 4 +3-2 Al 2 (SO 4 ) 3 Cu +2 CuSO 4 Put brackets around the SO 4 to indicate 3 sulphate ions, not 43 oxygen atoms SO 4 -2 Don’t forget the roman numeral since copper has more than one combining capacity