What role do functional groups play in determining chemical properties?

Functional groups determine the chemical properties of a molecule by influencing its reactivity, polarity, and phase of matter.

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. They are the centres of reactivity in a molecule. The same functional group will undergo the same or similar chemical reactions regardless of the size of the molecule it is a part of. This allows for systematic prediction of chemical reactions and behaviour of chemicals.

For instance, alcohols have a hydroxyl (-OH) functional group. This group is polar, making alcohols polar as well. This polarity allows alcohols to form hydrogen bonds with other molecules, leading to properties such as high boiling points and solubility in water. Similarly, carboxylic acids contain a carboxyl (-COOH) group, which makes them acidic. The presence of this functional group allows carboxylic acids to donate a proton (H+) in a reaction, a characteristic behaviour of acids.

Functional groups also play a significant role in determining the phase of matter at room temperature. For example, compounds with large hydrocarbon chains are typically solids, while those with smaller chains or more polar functional groups are often liquids or gases.

In addition, functional groups can influence how a molecule interacts with light, which can be important in contexts such as colour (in dyes and pigments) and ultraviolet protection (in sunscreens). For example, the conjugated double bonds in carotenoids (a type of pigment) absorb light in the visible range, giving them their characteristic colours.

In summary, functional groups are key in determining a molecule's chemical properties. They influence reactivity, polarity, and phase of matter, among other characteristics, allowing chemists to predict and understand the behaviour of different molecules.