HCl_(aq)H⁺¹ + Cl^-1        produces H⁺¹ in water
NH_3(aq)NH₄⁺¹  +  OH^-1   produces OH^-1 in water
Although NH₃ does not contain OH^-1, hydroxide ions form when added to water.
Arrhenius acid and base neutralize each other to produce salt and water:
HCl_(aq) + NaOH_(aq)NaCl_(aq) + H₂0_(l)
H⁺¹_(aq) + OH^-1_(aq) H₂0_(l)

Arrenhius theory most limited of the three theories since it requires reactions be aqueous and applies only to substances producing H₃O⁺¹ or OH^-1.

2. Bronsted/Lowry Theory
     Johannes Bronsted (1879-1947)
     Thomas Lowry (1874-1936)
In 1923, Bronsted (Danish) and Lowry (English) published independent papers on the same subject. Unlike the Arrenhius theory, their approach was not limited to aqueous solutions but for all proton (H+) containing systems.

ACID:  Substance that can donate proton (H⁺¹).
BASE:  Substance that can accept proton (must contain lone pair of electrons).

Acids may be cations, neutral molecules, or anions, while bases may be anions or neutral molecules.  Just as a reduction must always accompany an oxidation, a proton donor (acid) must accompany a proton acceptor (base).  Once an acid transfers its proton it becomes the conjugate base (CB) and once a base accepts the proton it becomes the conjugate acid (CA).  Since protons are always transferred in the Arrenhius concept, all Arrhenius acid/base reactions are also Bronsted-Lowry acid/base reactions.
But if water is not involved (HCl & NH3), the reaction can be explained by Bronsted/Lowry concept and not Arrenhius.  (Some remarks on the concept of acids and bases by Bronsted).
HCl  +  NH₃  NH₄⁺¹  +  Cl^-1
acid      base       CA         CB
Bronsted/Lowry expands Arrenhius to include any proton transfer (water not requirement).

3. Lewis Theory
     Gilbert Lewis (1875-1946)
Just as the Arrenhius theory did not support observations of acid-base behavior in nonaqueous systems, the Bronsted-Lowry model excluded nonprotonated systems. Lewis suggested his theory in a 1923 book "Thermodynamics and the Free Energy of Chemical Substances" and fully developed the theory in 1938.

ACID:  Substance that can accept a pair of electrons from another atom to form a new bond.
BASE:  Substance that can donate a pair of electrons to another atom to form a new bond.

The product of Lewis acid-base reaction referred to as adduct. The proton itself can act as Lewis acid. Lewis expands acid/base reactions to include many substances without H in formula.
F₃B  +  :NH₃ F₃B:NH₃     Explained by Lewis but not Arrenhius or BL
acid      base        adduct

All Bronsted/Lowry acid/base reactions are also Lewis acid/base reactions.

Which theories can explain the following?
HI + H₂OH₃O⁺¹ + I^-1      Explained by all 3 theories
HI  +  NH₃NH₄⁺¹ + I^-1    Explained by BL & Lewis
I₂ + NH₃NH₃I⁺¹ + I^-1      Explained by Lewis
I₂  +  Cl ICl + I             Cannot be explained by any of the theories
X:^-1 + Y⁺¹Y:X                  Explained by Lewis but not Arrenhius or BL
H₂ + Cl₂ 2HCl                Cannot be explained by any of the theories!

Answer (a)-(e) based on the following equation: XY + X₂Z X₃Z⁺¹ + Y^-1
(a) What is needed in the equation to be Arrenhius acid-base reaction?
(b) What is needed in reaction to be Bronsted/Lowry acid-base reaction?
(c) What is needed in reaction to be Lewis acid-base reaction?
(d) Using the equation, why is Bronsted-Lowry more general than Arrenhius?
(e) Using the equation, why is Lewis more general than Bronsted-Lowry?
Answers: (a) X = H  &  Z = O     (b) X = H      (c) Z must possess lone pair in X₂Z
(d) X₂Z not limited to H₂O  and X not limited to H   (e) X not limited to H