The lack of a fixed form in gaseous substances stems from the weak intermolecular forces present. Unlike solids, where molecules are tightly bound in a rigid lattice, or liquids, where molecules are closely packed but can move past one another, gas molecules possess negligible attraction. This allows them to move freely and independently, expanding to fill the entire volume of any container they occupy. An example is the diffusion of a gas, such as helium, released from a balloon; it spreads throughout the room instead of maintaining a defined form.
This characteristic is crucial to many natural processes and industrial applications. It enables efficient mixing and distribution of substances, essential in atmospheric phenomena, combustion engines, and chemical reactions. Historically, understanding this property has been fundamental to advancements in thermodynamics, fluid mechanics, and the development of technologies involving compressed gases.