Ionization and dissociation

Dissociation and ionization are two different concepts, with certainoverlapping.

"Dissociation"involves breaking of bonds : usually covalent bonds and ionic bonds.
"Ionization" involves the formation of charged species from unchargedspecies, or the formation of higher-charged species fromcharged species.

e.g. HCl(g) + aq → H⁺(aq) + Cl⁻(aq)
dissociation(√) and ionization(√).
It involves thebreaking of H-Cl bonds in HCl molecules (dissociation) to form H⁺(aq) and Cl⁻(aq) ions(ionization).

e.g. CH3COOH(g) + aq ⇌ H⁺(aq) + CH3COO⁻(aq)
dissociation(√), ionization(√).
It involves thebreaking of O-H bonds in CH3COOH molecules(dissociation) to form H⁺(aq) and CH3COO ⁻(aq) ions (ionization).

Refer to the above 2 examples. Both of the terms dissociation and ionizationcan be used to describe such reaction of all acids.
In F.4, it is usually said that "an acid is ionized in water". In F.5/6, the term"dissociation constant" is more frequently used than the term"ionization constant" for the equilibrium constant ofdissociation/ionization of a weak acid/base in water.

e.g. Na⁺Cl⁻(s) + aq → Na⁺(aq) + Cl⁻(aq)
dissociation(√), ionization(x)
It involves theseparation of opposite ions by breaking of ionic bonds (dissociation), but thenumber and nature of charged species (ions) remain unchanged (not ionization).

e.g. HCO3⁻(aq) ⇌ H⁺(aq) + CO3²⁻(aq)
dissociation(√), ionization(√)
It involves the breakingof O-H bonds in HCO3⁻ ions (dissociation) to form H⁺(aq) + CO3²⁻(aq) ions (ionizationas higher-charged species areformed).

e.g. Na(g) → Na⁺(g) + e⁻
dissociation(x), ionization(√)
It does not involve breaking of bonds (not dissociation). Neutral sodium atomsrelease electrons to give sodium ions (ionization).

e.g. Cl(g) + e⁻ → Cl⁻(g)
dissociation(x), ionization(x).
It does not involvebreaking of bonds (not dissociation). The number of charges species (electronsor chloride ions) remain unchanged (not ionization).

thank you!

001 is wrong...
please refer to
http://hk.knowledge.yahoo.com/question/question?qid=7011020300474
for the answer.

dissociation=completely
ionization=slightly

How to determine if the equation should be dissociation or ionization?

strong acid/alkali=dissociation
for example,NaOH,HCl

weak acid/alkali=ionization
for example, CH3COOH,NH3(aq)