What is meant by the expression homologous series? Give an example of one.

Organic compounds are essentially the chemical building blocks of all living things, as well as many materials we use in our daily lives. They mainly consist of carbon atoms bonded to hydrogen, oxygen, nitrogen, or other elements in various configurations.

One of the most distinguishing features of organic chemistry is the vast diversity of structures and functions that can arise from the versatile carbon atom. Carbon can form four covalent bonds with other atoms, leading to an infinite array of molecular structures.

These compounds play crucial roles in biological processes and industrial applications alike. From the DNA that codes our genetic information to the fuels that power our vehicles, organic chemistry is fundamental to both the natural and engineered aspects of our world.

A functional group in organic chemistry is a specific group of atoms within a molecule that is responsible for the characteristic chemical reactions of that molecule. It's like a distinctively active area of a molecule that participates in chemical reactions.

Functional groups are critical in determining the properties and reactivity of organic compounds. There are many different functional groups, each with its own set of chemical behaviors. For example, an alcohol group (−OH) makes a compound polar and capable of forming hydrogen bonds, while a carboxyl group (−COOH) gives acidic properties to the compound.

The presence of a functional group can drastically change the nature of an organic compound, leading to a wide range of potential chemical activities even among molecules that have similar carbon skeletons.

Alkanes represent the simplest class of organic compounds made up exclusively of carbon and hydrogen atoms, connected by single bonds. They belong to a larger group known as hydrocarbons. Because their carbon atoms are fully saturated with hydrogen, alkanes are considered to be 'saturated hydrocarbons'.

The simplest alkane is methane, where a single carbon atom is bonded to four hydrogen atoms. Each succeeding member in the series adds a CH2 unit to the molecular chain, indicating a homologous relationship among them. The molecular formulas for alkanes follow the general pattern of \(C_nH_{2n+2}\), where 'n' indicates the number of carbon atoms.

Alkanes are usually unreactive due to the strength of the carbon-hydrogen bonds and the lack of a functional group. This makes them valuable as a stable source of energy in the form of fuels like propane and butane.