IONIC BONDING

• More stability
• Atoms want to achieve a lower energy state
• Think of this like potential energy, what is the potential energy of a book to fall off a desk?
o PE = mgh
• Look at potential energy graph
• What is the potential for Potassium to form a potassium ion?
K
Energy
K+
• When a potassium ion forms, energy is released (negative value). This is exothermic
• When atoms form ions they are electrostatically attracted to ions of opposite charge 􀃆 Ionic bond
How do ions bond?
• Ions bond so that the compound has no charge
• Positive charges are balanced by negative charges
o Ex: NaCl, +1 charge of Na+ balances the -1 charge of Cl-
o Ex: FeCl2, +2 carge of Fe+2 balances the two -1 charges of the Cl- ions.
How do we write chemical formulas of ionic compounds?
• Write cation first, anion second
• Make sure charges cancel out
• When balancing charge using polyatomic ions, act as if polyatomic ion is one atom.
o Ex: NaHCO3, +1 charge of Na+ balances -1 charge of HCO3-
o Ex: NH4OH, +1 charge of NH4+ balances -1 charge of OH-
• When you have to use more than one polyatomic ion, use parentheses
o Ex: Fe(OH)3
o Ex: Al2(SO4)3
• When dealing with two ions that have unequal charges, make the charge of one be the subscript of the other and vice versa
o Ex: Al2O3.
􀂃 Charge of O2- is 2, so make 2 subscript on Al
􀂃 Charge of Al3+ is 3, so make 3 subscript on O
How do we write the names of compounds?
• Write the cation first than the anion
• For transition metals which have more than one oxidation state, use number in parentheses to describe charge.
o FeCl2 = Iron (II) Chloride
o FeCl3 = Iron (III) Chloride
Old names:
• If you use the old names, you don’t need to use numbers in parentheses
Ferrous = Iron (II)
Ferric = Iron (III)
Cuprous = Copper (I)
Cupric = Copper (II)
Mercurous = Mercury (I)
Mercuric = Mercury (II)
Stannous = Tin (II)
Stannic = Tin (IV)
• Examples
o FeCl2 = Ferrous Chloride
o FuCl2 = Cupric Chloride