Rules of Acidity and Conjugate Base Stability

Vocabulary flashcards covering the five rules of base stability and acidity, along with key organic and inorganic acid pKa values.

Most Stable Base

The weakest base when comparing two bases, corresponding directly to having the strongest conjugate acid.

Size / Polarizability Effect

A rule of stability stating that a negative charge is stabilized on a larger atom because larger atoms are more polarizable and possess lower electron density.

Resonance Delocalization

A method of spreading out negative charge that stabilizes a base and indicates which lone pair is protonated in molecules possessing two or more receptor sites.

Periodic Electronegativity Trend in Acidity

The principle that acidity increases from left to right across a period on the periodic table as negative charge is placed on a more electronegative atom.

Inductive Effect (Electrostatic Stabilization of the Anion)

An attractive stabilization of an anion resulting from bonding to a more electronegative atom that creates a significant bond dipole with a partial positive charge ($\delta^+$), an effect that diminishes rapidly with distance.

s-Character Effect

A stabilization factor where having more s character on the atom bearing the negative charge increases base stability, allowing comparison of the acidities of alkanes, alkenes, and alkynes.

Acetylene ($HC \equiv CH$)

An alkyne with a $pK_a$ of $25$, which forms the conjugate base $HC \equiv C^-$.

Ethanol ($CH_3CH_2OH$)

An alcohol with a $pK_a$ of $15.9$, which forms the conjugate base $CH_3CH_2O^-$.

Water ($H_2O$)

A neutral inorganic compound with a $pK_a$ of $15.7$, which forms the conjugate base $HO^-$.

Acetic Acid ($CH_3COOH$)

A carboxylic acid with a $pK_a$ of $4.76$, which forms the conjugate base $CH_3COO^-$.

Hydrogen Chloride ($HCl$)

A strong acid with a $pK_a$ of $-7$, which forms the conjugate base $Cl^-$.

Hydronium Ion ($H_3O^+$)

An acidic species with a $pK_a$ of $-1.74$, which forms the conjugate base $H_2O$.

Ethylene ($CH_2=CH_2$)

An alkene with a $pK_a$ of $44$, which forms the conjugate base $CH_2=CH^-$.

Methane ($CH_4$)

An alkane with a $pK_a$ of $60$, which forms the conjugate base $CH_3^-$.