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Gases – Definition, Examples, List of the Elements, and More

Gases Definition

A gases define as a state of matter consisting of particles with neither an illustrated volume nor a defined shape. It is one of the four fundamental states of matter, along with solids, liquids, and plasma.

Under ordinary conditions, the gas state is between the liquid and plasma states. A gas may consist of atoms of one element (e.g., H2, Ar) or compounds (e.g., HCl, CO2) or mixtures (e.g., air, natural gas).

Examples of Gases


Whether or not a substance is a gas depends on its temperature and pressure. Examples of gases at standard temperature and strain include:

  • air (a mixture of gases)
  • chlorine at room temperature and pressure
  • ozone
  • oxygen
  • hydrogen
  • water vapour or steam

List of the Elemental Gases

There are 11 elemental gases (12 if you count ozone). Five are homonuclear molecules, while six are monatomic:

  • H2 – hydrogen
  • N2 – nitrogen
  • O2 – oxygen (plus O3 is ozone)
  • F2 – fluorine
  • Cl2 – chlorine
  • He – helium
  • Ne – neon
  • Ar – argon
  • Kr – krypton
  • Xe – xenon
  • And also, Rn – radon

Except for hydrogen, which is at the top left side of the periodic table, elemental gases are on the table’s right side.

Properties of Gases

  • Particles in a gas are widely separated from each other.
  • They resemble an “ideal gas” at low temperature and ordinary pressure in which the interaction between the particles is negligible, and collisions between them are entirely elastic.
  • At higher pressures, intermolecular bonds between gas particles have a more significant effect on the properties.
  • Because of the space between atoms or molecules, most gases are transparent.
  • A few are faintly coloured, such as chlorine and fluorine.
  • Gases tend not to react as much as other states of matter to electric and gravitational fields.
  • Compared with liquids and solids, gases have low viscosity and low density.

Origin of the Word “Gases”

  • The word “gases” was coined by 17th-century Flemish chemist J.B. van Helmont. There are two theories about the origin of the story.
  • Helmont’s phonetic transcription of the Greek word Chaos, with the g in Dutch, pronounced the chin chaos.
  • Paracelsus’s alchemical use of “chaos” referred to rarified water. The other theory is that van Helmont took the word from geist or guest, which means spirit or ghost.

Gases vs Plasma

  • A gas may contain electrically charged atoms or molecules called ions. It’s common for gas regions to have random, transient authorised parts because of van der Waals forces.
  • Ions of like charge repel each other, while ions of opposite direction attract each other.
  • If the fluid consists entirely of charged particles or if the particles are permanently assigned, the state of matter is plasma rather than a gas.

The State of Gases


The following properties characterize the gases state of matter:

  • Its volume not fix; it will expand to fill a container – unlike solids and liquids
  • It is compressible – its work changes when pressure changes – unlike solids and liquids, gases are fluids
  • To flow. Their shapes adapt to that of their containers
  • The atoms or molecules in a gas are spread much more thinly than the particles in solids and liquids.
  • For example, at a temperature of 0 °C and pressure of 1 atm, 1 mole of water has a volume of 18 ml in the liquid state and 22.4 litres in the vapour state.
  • At 0 °C and 1 atm, a small vapour exists in equilibrium with liquid/solid water.

Physical Characteristics of Gases

  1. Because most gases are difficult to observe directly, they describe using four physical properties or macroscopic characteristics: pressure, volume, number of particles (chemists group them by moles) and temperature.
  2. These four characteristics were repeatedly observed by scientists such as Robert Boyle, Jacques Charles, John Dalton, Joseph Gay-Lussac and Amedeo Avogadro for various gasses in various settings.
  3. Their detailed studies ultimately led to a mathematical relationship among these properties expressed by the ideal gas law (see simplified models section below).
  4. Gas particles widely separate from one another, and consequently, have weaker intermolecular bonds than liquids or solids.
  5. These intermolecular forces result from electrostatic interactions between gas particles. Like-charged areas of different gas particles repel, while oppositely charged regions of foreign gas particles attract one another, gases that contain permanently charged ions know as plasmas.
  6. Gaseous compounds with polar covalent bonds have permanent charge imbalances and experience relatively strong intermolecular forces, although the molecule while the compound’s net charge remains neutral.
  7. Transient, randomly induced charges exist across non-polar covalent bonds of molecules, and electrostatic interactions caused by them refer to as Van der Waals forces.
  8. Intermolecular forces’ interaction varies within a substance that determines many of the physical properties unique to gas.
  9. A comparison of boiling points for compounds formed by ionic and covalent bonds leads us to this conclusion.
  10. The drifting smoke particles in the image provides some insight into low-pressure gas behaviour.
  11. Compared to the other states of matter, gases have low density and viscosity. Pressure and temperature influence the particles within a specific volume.
  12. This variation in particle separation and speed refer to as compressibility. This particle separation and size influences the optical properties of gases, as shown in the following refractive indices list.
  13. Finally, gas particles spread apart or diffuse to distribute themselves throughout any container homogeneously.


Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may make up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or compound molecules made from a variety of bits (e.g. carbon dioxide).

A gas mixture, such as air, contains a variety of pure gases. What distinguishes a gas from liquids and solids is the vast separation of the individual gas particles. This separation usually makes a colourless gas invisible to the human observer.

The interaction of gas particles in the presence of electric and gravitational fields are considered[by whom?] negligible, as indicated by the constant velocity vectors.

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