Understanding Different Acid-Base Theories: Arrhenius, Brønsted-Lowry, and Lewis

1. What Are They?

   • Arrhenius Theory: This theory says that an acid is a substance that makes more $H^+$ ions (hydrogen ions) in water. A base, on the other hand, makes more $OH^-$ ions (hydroxide ions). For example, when you mix hydrochloric acid (HCl) in water, it breaks down to release $H^+$. Meanwhile, sodium hydroxide (NaOH) breaks down to release $OH^-$.

   • Brønsted-Lowry Theory: According to this theory, an acid is something that donates a proton (which is basically a $H^+$ ion), while a base is something that accepts a proton. For example, in the reaction where HCl mixes with water ($HCl + H_2O \rightarrow Cl^- + H_3O^+$), HCl gives a proton to water, so we call HCl an acid.

   • Lewis Theory: This theory defines an acid as something that can accept an electron pair (which is a pair of electrons), and a base as something that donates an electron pair. For example, when boron trifluoride (BF$_3$) reacts with ammonia (NH$_3$), BF$_3$ accepts an electron pair from NH$_3$.

2. Where Do They Apply?

   • Arrhenius: This theory is mostly about reactions in water. It doesn’t really look at reactions that happen outside of water.

   • Brønsted-Lowry: This theory is more flexible because it can apply to reactions in gases and other environments, not just in water.

   • Lewis: The Lewis theory is the most general. It includes all kinds of reactions, even the more complicated ones.

3. Some Simple Examples:

   • Arrhenius: When HCl breaks apart in water, it becomes $H^+$ and $Cl^-$.

   • Brønsted-Lowry: When carbonic acid (H$_2$CO$_3$) breaks down, it produces $H^+$ and bicarbonate ($HCO_3^-$).

   • Lewis: When BF$_3$ interacts with NH$_3$, they form a connection: $BF_3 + NH_3 \rightarrow F_3B-NH_3$.

4. How Widely Do They Work?

   • Arrhenius: This theory mostly explains basic acid-base reactions and doesn't cover much else.

   • Brønsted-Lowry: This theory is good at explaining about 85% of acid-base reactions that happen in different liquids.

   • Lewis: The Lewis theory covers almost everything related to acid-base reactions, explaining over 90% of them.

Now you have a clearer picture of these three important acid-base theories!