Johannes Nicolaus Brønsted a man from Denmark and Thomas Martin Lowry another man from England. Both of these men independently released their theory, which became the reason why it's called Brønsted–Lowry theory.
This Theory contains the missing pieces of the Arrhenius Theory (Acid donates protons H⁺ ion and Base donates hydroxide OH⁻).
It also contains how acids (any substance with pH below 7) and bases (any substance with pH above 7) interact.
Okay, Okay, now what makes Brønsted–Lowry Theory different... Acid (AKA proton donor and does not need to have pH below 7) the dude who donates a proton ( H⁺ ion ) is still the same here. Whatever it may be, if it donates a proton then it's an acid. However, on the other hand, the Base (AKA proton acceptor and does not need to have a pH above 7) is the dude who takes these protons, which holds the difference. This also explains why Ammonia NH₃ can act as a Base without having any OH⁻.
More info?
Well, it may also seem like any molecule containing hydrogen can be acid. but guess what? For it to be an acid the hydrogen in the molecule has to have a slight positive charge. This occurs when the hydrogen is bonded to a very electronegative atom ( electronegativity is described as the strength of an atom to pull electrons towards itself) like chlorine.
Whereas, if we look at Bases, they also need to meet a requirement. And that requirement is the existence of lone pairs(a pair of electrons that is free and not involved in bonds). If a lone pair of electron exists then it can form a dative covalent bond ( Basically just one of the atoms is the provider for electrons both atoms are sharing.... Sounds a bit unfair but it is what it is ) with the proton.
Example time? Perhaps...
You might have noticed, Acid and Base interact in pairs, cause if one donates the other has to accept the donation, hence CONJUGATE ACID-BASE PAIRS.
When an acid like HCl dissolves in water it establishes an equilibrium as follows
HCl (aq) + H₂O (l) ⇌ H₃O⁺ (aq) + Cl⁻ (aq)
What in the world is a H₃O⁺?
Well, it's a hydronium ion, happens when water accepts a proton.
Also, have you noticed anything else? Yes, if the acid donates a proton it turns into a base... So... they form pairs...
HCl and Cl⁻ as a conjugate pair while H₂O and H₃O⁺ is the other conjugate pair.
Example 2? Maybe...
This example will make something else apparent. It is ammonia dissolved in water, it establishes another equilibrium.
NH₃ (aq) + H₂O (l) ⇌ NH₄⁺ (aq) + OH⁻ (aq)
Here the conjugate pairs are. For the base H₂O & OH⁻ and as for acid NH₃ & NH₄⁺.
There something else in both these reactions to notice... again...
It is Water! seen how it can act as both as an acid and base, because of this that are called amphoteric substances.
Speaking of amphoteric substances, There are strange substances that do not donate or accept protons! but they do act like acids and bases... But How? Why? Now the Lewis Theory comes into play. What does Lewis theory say that makes it different? It involves the transfer of electrons instead of protons. Where acid is an electron acceptor and a base is an electron donor.
Here are names for the types of acids
Monoprotic - donates a single hydrogen
Diprotic - donates two hydrogen
Triprotic - donates three hydrogen
The Bases goes the same way...
Monobasic - accepts a single proton
Dibasic - accepts two protons
Tribasic - Blah Blah you know the drill...
What makes an Acid weak or Strong?
The acid that dissociated completely are strong. HCl (aq) → H⁺ (aq) + Cl⁻ (aq)
The acid that dissociated partially are weak. CH₃COOH (aq) ⇌ CH₃COO⁻ (aq) + H⁺ (aq)
Why did I post something boring like this? I ask myself that... Quarantine is getting me bored...