What are molecules primarily composed of?

Molecules are primarily composed of atoms, which are the basic building blocks of matter. Atoms themselves consist of a nucleus made up of protons and neutrons, surrounded by electrons. When atoms bond together, they form molecules, which can be simple two-atom structures like diatomic molecules (e.g., O2) or complex structures made up of many different atoms (e.g., glucose, C6H12O6). This fundamental concept is essential in understanding chemical compounds and reactions, which are key topics within HVAC systems, particularly when discussing refrigerants and materials involved in the refrigeration process.