Glossary
Acid Strength
A measure of how readily an acid donates a proton (H+) in solution. Strong acids completely dissociate, while weak acids only partially dissociate.
Example:
Hydrochloric acid (HCl) is a strong acid because it fully ionizes in water, releasing all its H+ ions.
Base Strength
A measure of how readily a base accepts a proton (H+) or donates a hydroxide ion (OH-) in solution. Strong bases completely dissociate or ionize, while weak bases only partially do so.
Example:
Sodium hydroxide (NaOH) is a strong base commonly used in titrations due to its complete dissociation.
Bond Strength (Acidic H-X bond)
The energy required to break the bond between the acidic hydrogen and the atom it's bonded to (X). Weaker H-X bonds lead to stronger acids because the proton is more easily released.
Example:
The H-I bond has a lower bond strength than the H-F bond, making HI a much stronger acid than HF.
Carboxylic Acids (R-COOH)
Organic acids characterized by a carboxyl group (-COOH). They are generally weak acids due to the relatively low electronegativity of the carbon atom in the carboxyl group.
Example:
Acetic acid (), found in vinegar, is a common carboxylic acid and a weak acid.
Conjugate Acid
The species formed when a base accepts a proton. A strong base produces a weak, stable conjugate acid.
Example:
When ammonia () accepts a proton, it forms the ammonium ion (), which is its conjugate acid.
Conjugate Base
The species formed when an acid donates a proton. A strong acid produces a weak, stable conjugate base.
Example:
When acetic acid () donates a proton, it forms the acetate ion (), which is its conjugate base.
Dissociation (Acids/Bases)
The process by which an acid or base breaks apart into ions when dissolved in water. Strong acids/bases undergo complete dissociation, while weak ones undergo partial dissociation.
Example:
When is added to water, it undergoes complete dissociation into and ions.
Electronegativity (Acid Strength context)
A measure of an atom's ability to attract electrons in a chemical bond. In oxyacids, higher electronegativity of 'Z' pulls electron density from the O-H bond, increasing its polarity and acid strength.
Example:
The high electronegativity of chlorine in makes the O-H bond very polar, contributing to its strong acidity.
Halogenic Hydrides (HX)
Binary acids formed between hydrogen and a halogen element (F, Cl, Br, I). Their acid strength increases down the group due to decreasing H-X bond strength.
Example:
Among the halogenic hydrides, HI is the strongest acid because the H-I bond is the weakest.
Lewis Structures
Diagrams that show the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule. They are crucial for visualizing molecular structure and predicting properties like acid strength.
Example:
Drawing the Lewis structure for helps visualize the central sulfur atom bonded to oxygen atoms, which is key to understanding its acidic properties.
Oxidation State (Acid Strength context)
The hypothetical charge an atom would have if all bonds were ionic. In oxyacids, a higher oxidation state of the central atom 'Z' increases the polarity of the O-H bond, leading to a stronger acid.
Example:
Comparing and , the higher oxidation state of chlorine in (Cl is +7) makes it a much stronger acid than (Cl is +1).
Oxyacids (HOZ)
Acids where the acidic hydrogen is bonded to an oxygen atom, which is in turn bonded to another non-metal atom 'Z'. Their strength depends on the electronegativity and oxidation state of 'Z'.
Example:
Sulfuric acid () is a common oxyacid where sulfur is the central atom 'Z'.
Periodic Trends (Acid Strength)
Observable patterns in acid strength across periods and down groups in the periodic table. Acid strength generally increases across a period (due to electronegativity) and down a group (due to atomic size/bond strength).
Example:
Understanding periodic trends helps predict that is a stronger acid than because sulfur is below oxygen in the periodic table.