Chemical Bonding - Ions and Metals: Formulas of Ionic Compounds

Question 1

formulas for ionic compounds

Answer 1

• formulas can be written to balance the magnitude of charge from each ion so that compound is neutral
• positive ion first followed by negative ion (cation-anion)
• K^+ + Br^- –> K Br
• number of ions present indicated with subscripts after each ion
• Cu^2+ + Cl^- –> Cu Cl_2
• monoatomic ions contain only one atom
• oxidation number is the charge on the atom
• group IA (1), group IIA (2) - (+) oxidation # = group #
• group VA (15), VIA (16), VIIA (17) - (-) oxidation 3 = group 3 - 8 (18)

Question 2

shortcut method

Answer 2

• AL^3+ S^2- (Al_2 S_3)
• check if subscripts are lowest possible
• different oxidation numbers require parentheses around polyatomic ion
• Ca ^2+ OH^- –> Ca(OH)_2
• some oxidation numbers are written without parentheses around polyatomic ion
• K^+ OH^- –> KOH

Question 3

polyatomic ions

Answer 3

• charged species with many atoms

- behave as a unit, do not separate