Forming Ionic Bonds
• Electron transfer:
one atom loses electrons - another atom
gains those electrons
• Positive and negative ions attract = ionic
compound.
• Metal + oxygen = OXIDE
• Metal + nonmetals = SALT
Ionic Bonds
• Often binary (2 elements)
• e- lost = e- gained (always)
• Quick check:
– How will sodium & chlorine combine?
– How about calcium & sulfur?
– How about lithium & phosphorus?
– How about iron (III) & oxygen?
Hint: use e- configurations or electron dot diagrams
Then show box and table method to solve
Quick Check
– How will sodium & chlorine combine? calcium &
sulfur? lithium & phosphorus? iron (III) & oxygen?
Properties of Ionic Compounds
• Crystals (not molecules) = many cations
and anions packed into a repeating pattern
(crystal lattice).
• Chemical formula = ratio of atoms needed
• Fairly strong bond = large amount of
energy to break.
• High melting & boiling points
• Often rigid & hard
More Properties
• If a liquid or solution,
good conductors of electricity (electrolytes)
• If a solid, bad conductors because ions aren’t
free to move
• EXOTHERMIC (almost always) –
means the ionic compound is more stable &
requires less energy, so heat is given off when
forming
Ex: hand warmers = iron + oxygen combining
Lattice Energy
•
•
•
•
Energy to break apart 1 mole of ions
Equals energy released when ions form
More negative number = stronger bonds
Smaller ions = greater lattice energy
(nucleus is closer to the valence e-)
• Greater ionic charge = greater lattice NRG
Quick Check
• Which would have the greater lattice
energy?
– LiCl or LiBr
– KF or RbF
– NaCl or MgF2
– SrCl2 or MgO
• Which compound in each pair would have
the higher melting point?