Ch. 6 Bonding
6.3 Ionic Bonding
Ionic Compounds



ionic bonds do NOT form molecules
chemical formulas for ionic
compounds represent the simplest
ratio of ion types
made of anions and cations
Ionic Compounds



combined so that positive charges
balance negative charges
crystalline solid
formula of ionic compound depends
of the charges of the ions combined
Binary Ionic Compounds

Because positive charges must balance
negative charges, use criss-cross method to
make formulas. Write the formula for
aluminum oxide.
Binary Ionic Compounds
If you don’t like criss-cross, use
algebra. Write the formula for
barium sulfide.
Formation

attractive forces:
• oppositely charged ions (main attraction)
• nuclei and electron clouds of adjacent ions

repulsive forces:
• like-charged ions (main repulsion)
• electrons of adjacent ions
Formation


distance between
the ions creates a
balance between
those forces
ions minimize their
PE by combining in
an orderly
arrangement called a
crystal lattice
Formation
Specific lattice pattern
created depends on:
 charges of ions
• determines number of
electrons transferred
• determines the ratio of ions

size of ions
• larger ions need more space
Lattice Energy



energy released when
separate gaseous ions bond
to form ionic solid or the
energy absorbed to break
the bonds between ions
the larger the amount of
energy, the stronger the
bond
more electrons transferred
or smaller ions leads to a
larger lattice energy
NaCl
-787.5
NaBr
-751.4
CaF2
-2634.7
CaO
-3385
LiCl
-861.3
MgO
-3760
KCl
-715
In each of the following pairs of
compounds, identify the one with
the higher lattice energy

KCl, CaS

LiF, NaCl

Fe2O3, MnO2

CaO, CaCl2