气体中的颗粒彼此广泛分离。在低温和常压下，它们类似于“理想气体”，其中颗粒之间的相互作用可以忽略不计，并且它们之间的碰撞是完全弹性的。在较高压力下，气体颗粒之间的分子间键对性质具有更大的影响。由于原子或分子之间的空间，大多数气体是透明的。一些是微弱的颜色，如氯和氟。气体往往不会像其他物质状态那样对电场和引力场作出反应。与液体和固体相比，气体具有低粘度和低密度。 “气体”这个词是由17世纪佛兰德化学家J.B. van Helmont创造的。关于这个词的起源有两种理论。一个是Helmont的希腊词Chaos的语音转录，荷兰语中的g发音像混乱中的ch。 Paracelsus对“混乱”的炼金术用法指的是稀薄的水。另一个理论是van Helmont从geist或gahst中获取了这个词，意思是精神或幽灵。气体可含有带电的原子或称为离子的分子。实际上，由于范德华力，气体区域通常包含随机的瞬态带电区域。相同电荷的离子相互排斥，而相反电荷的离子相互吸引。如果流体完全由带电粒子组成或者如果粒子是永久带电的，则物质状态是等离子体而不是气体。
The particles in the gas are widely separated from each other. At low temperatures and pressures, they are similar to “ideal gases” where the interaction between the particles is negligible and the collision between them is completely elastic. At higher pressures, the intermolecular bond between gas particles has a greater impact on properties. Most gases are transparent due to the space between atoms or molecules. Some are weak colors such as chlorine and fluorine. Gases often do not react to electric fields and gravitational fields like other material states. Gases have low viscosity and low density compared to liquids and solids. The word “gas” was coined by the 17th century Flemish chemist J.B. van Helmont. There are two theories about the origin of the word. One is the transcription of the Greek word Chaos of Helmont, and the g in Dutch is pronounced like ch in chaos. Paracelsus’s alchemy usage of “chaos” refers to thin water. Another theory is that van Helmont obtained the word from geist or gahst, meaning spirit or ghost. The gas may contain charged atoms or molecules called ions. In fact, due to van der Waals forces, gas regions typically contain random transient charged regions. Ions of the same charge repel each other, while ions of opposite charges attract each other. If the fluid consists entirely of charged particles or if the particles are permanently charged, the state of matter is a plasma rather than a gas.