Ionic bonding —> electrostatic attraction between positive & negative ions. It holds together cations & anions in ionic compounds
Ionic compounds —> metal + non-metal
Ionic structure = giant ionic lattice
each ion is surrounded by oppositely charged ions, forming a giant ionic lattice
solids at room temperature
high energy needed to overcome strong, electrostatic attraction between ions
high melting and boiling points
many ionic compounds dissolve in polar solvents (e.g: water)
compounds with large charges —> ionic attraction may be too strong, for water to be able to break down the lattice —> compound will not be very soluble
Solubility requires 2 main processes:
ionic lattice must be broken down
water molecules must attract and surround ions
In the solid state:
ions are in fixed position in the giant ionic lattice
there are no mobile charge carriers
non-conductor of electricity in solid state
When liquid or dissolved in water:
Solid ionic lattice breaks down
ions are now free to move as mobile charge carriers
is an conductor of electricity in liquid and aqueous states
covalent bonding —> strong electrostatic attraction between a shared pair of electrons and the nuclei of bonded atoms.
covalent bonding occurs between non-metallic elements, compounds of non-metallic elements and polyatomic ions
orbital overlap:
shared pair of electrons is attracted to the nuclei of both the bonding atoms
Bonded atoms often have outer shell with the same electron structure as the nearest noble gas
boron, phosphorus, sulfur and chlorine are exceptions —> can bond with more f atoms to have more than 8 electrons in the outer shell
In SF6, 6 unpaired electrons from sulfur are paired
the outer shell of sulfur now contains 12 electrons, more than the nearest noble gas argon
This is called expansion of the octet and is only from the n=3 shell, when a shell becomes available foe the expansion
Average bond enthalpy:
A measurement of covalent bond strength
The larger the value of the average bond enthalpy, the stronger the covalent bond