Functional groups are special groups of atoms in molecules that have unique properties and ways of reacting. They are very important because they help decide how organic compounds behave.

Let’s break it down:

1. Chemical Reactivity:

   • Different functional groups react in different ways.
   • For example, alcohols, which have a –OH group, are usually more polar. This means they can form hydrogen bonds, which helps them have higher boiling points compared to alkanes.
   • Also, if you change a functional group, it can really change how a compound reacts. For instance, when you turn alcohols into aldehydes or ketones, you change their properties.

2. Polarity and Solubility:

   • Functional groups that are polar, like –NH2 and –COOH, usually make molecules dissolve well in water.
   • On the other hand, compounds with non-polar functional groups, like alkanes, tend to dissolve better in organic solvents.

3. Biological Activity:

   • Functional groups also play a big role in how things work in living organisms.
   • For example, the carboxylic group (–COOH) is very important in amino acids, which are the building blocks of proteins. This affects how proteins are shaped and how they work.

In summary, over 80% of known organic compounds are sorted based on their functional groups. These groups directly affect the compounds' physical and chemical properties.