Gas: definition, history, types, laws, density

Methane, which is commonly burned on gas stoves with a blue flame, is often referred to simply as “gas.” It is extracted from underground gas fields. The gas, purified from harmful compounds, is sent through pipelines to factories and homes. In addition, gas is also produced from some oil wells. Gas can also be obtained by processing coal and shale, which are combustible rocks. Chemists make synthetic fibers from gas for weaving fabrics, bags for storing perishable foods, and many other things. But gas is not just methane. The oxygen we breathe is also a gas. Without oxygen, not a single match would burn. In order to quickly melt metal, blast furnaces and open-hearth furnaces are also blown with oxygen.

Another type of gas is carbon dioxide, which is added to the carbonated water we drink and gives it a pleasant taste. There are many types of gas. For example, air is made up of several gases. The main property of a gas is that it immediately takes up space. If you remove half of the air from a bottle, the remaining gas will spread out to fill the entire volume, though at a lower density. Gas is very useful to humans. Compressed air fills the tires of a car on earth, and in space it fuels rocket engines. Air controls pneumatic valves and blows fire into the bellows of a workshop.

It produces sound in wind instruments and moves sailboats across the water. Tubes with various advertisements are filled with various gas mixtures, a powerful stream of light is generated in a gas laser. Xenon gas is used to fill the tubes of photo lamps. Krypton gas protects the filament in electric lamps from burning.

The study of gases dates back to the 17th and 18th centuries, when scientists began to understand that air and other substances could exist in a gaseous form. One of the first major discoveries was made by the Scottish chemist Joseph Black (1728–1799), who, between 1756 and 1766, identified carbon dioxide, which he called "fixed air," as a distinct substance.

Shortly after, the French chemist Antoine Lavoisier (1743–1794) laid the foundation of modern chemistry. In the 1780s, he named oxygen and hydrogen, demonstrated that air consists of multiple gases, and helped systematize knowledge about chemical elements and gases.

Other notable discoveries include hydrogen, identified by the English scientist Henry Cavendish (1731–1810) in the 1760s, and nitrogen, discovered by the Scottish chemist Daniel Rutherford (1749–1819) in 1772. These early experiments showed that gases are distinct substances with their own properties.

The behavior of gases was studied quantitatively as well. Robert Boyle (1627–1691) formulated Boyle’s law in 1662, showing that gas volume decreases as pressure increases at a constant temperature. Later, Jacques Charles (1746–1823) discovered that gas volume expands with temperature, and Joseph Louis Gay-Lussac (1778–1850) studied the relationship between gas pressure and temperature, further refining the understanding of gaseous behavior.

By the late 18th century, scientists had established a clear concept of gases as a separate state of matter. These discoveries laid the groundwork for modern chemistry and physics, allowing gases to be studied, classified, and applied in countless ways.

Gases can be classified in several ways depending on their origin, properties, and usage:

Natural Gases

These gases occur naturally in the environment. The most common example is natural gas, which is primarily methane and is used as fuel for heating, cooking, and electricity generation. Other natural gases include oxygen (O₂), nitrogen (N₂), and carbon dioxide (CO₂) in the atmosphere.

Industrial or Synthetic Gases

These gases are produced artificially for specific purposes. Examples include ammonia (NH₃) for fertilizers, hydrogen (H₂) for chemical reactions and fuel, and industrial gases like argon, helium, and neon for welding, lighting, and cooling.

Flammable Gases

These gases can catch fire easily and are used as fuels. Examples are propane, butane, methane, and hydrogen. Safety precautions are essential when handling them.

Inert (Non-reactive) Gases

Also called noble gases, these do not easily react with other substances. Examples are helium, neon, argon, krypton, and xenon. They are used in lighting, welding, and creating controlled environments.

Toxic or Harmful Gases

Some gases are poisonous or harmful to humans and animals. Carbon monoxide (CO), chlorine (Cl₂), and hydrogen sulfide (H₂S) are examples. Proper ventilation and safety measures are critical when dealing with them.

Greenhouse Gases

These gases trap heat in the Earth's atmosphere and affect the climate. Important examples include carbon dioxide (CO₂), methane (CH₄), and water vapor (H₂O).

Medical or Special-purpose Gases

Gases used in medicine and specialized fields include oxygen for breathing support, nitrous oxide as an anesthetic, and medical-grade carbon dioxide for minimally invasive surgeries.

Gases don’t behave randomly — they follow clear patterns that scientists have been studying for centuries. For example, Boyle’s law shows that if you squeeze a gas, it pushes back harder while taking up less space. Heat it up, and according to Charles’s law, it eagerly expands. These laws help us understand everything from how balloons rise to why aerosol cans should never be left in the sun.

In textbooks, you’ll often meet the so-called “ideal gas” — a perfectly behaved model that never interacts with its neighbors. Real gases are more complicated: they attract, repel, and don’t always fit neatly into equations. Still, under ordinary conditions, many gases act close enough to ideal that we can predict their behavior surprisingly well.

One fascinating property of gases is how quickly they spread out. Open a bottle of perfume, and the scent seems to travel across the room almost instantly — that’s diffusion at work. Because gas particles move fast and have plenty of space between them, they mix and distribute themselves with remarkable speed.

Gases are incredibly light compared to liquids and solids. Their particles are so far apart that even a large volume of gas weighs very little. This is why warm air rises, storms form towering clouds, and helium balloons float and drift toward the sky. Low density is one of the qualities that makes gases so dynamic and unpredictable.

Heat a gas enough, and something extraordinary happens: it turns into plasma. In this state, particles become electrically charged and behave in striking new ways. Plasma lights up neon signs, flashes across the sky as lightning, and makes up the blazing surface of the sun. It’s a reminder that matter can transform into forms far more exotic than we encounter in everyday life.

Gases are everywhere around us, shaping life and the planet itself. The air we breathe is a delicate mixture that keeps humans, plants, and animals alive. Oxygen fuels our bodies, while carbon dioxide feeds the world’s vegetation. Some gases, like water vapor and carbon dioxide, also help regulate Earth’s climate by trapping heat — a natural process that can become dangerous when thrown out of balance.

Modern technology relies heavily on gases. Liquefied gases power cars and heat homes. Nitrogen and hydrogen are transformed into ammonia, which helps grow food for billions of people. Inert gases protect welding flames from contamination, while helium cools powerful scientific equipment. Wherever precision, energy, or controlled environments are needed, gases step in to do the job.

Because many gases are flammable, toxic, or stored under high pressure, safety is essential. Household gas, for example, has no smell — the odor we recognize is artificially added so leaks can be detected quickly. Gas cylinders must be stored upright and handled with care. A moment of negligence can turn a harmless container into a serious hazard, so proper precautions are non-negotiable.

Q: What is a gas?
A: A gas is a state of matter in which particles move freely, have no fixed shape, and expand to fill the space available.

Q: How is gas different from liquids and solids?
A: Unlike liquids and solids, gases do not have a definite shape or volume. Their particles are far apart and move rapidly, which allows gases to expand and compress easily.

Q: Can all substances become gases?
A: Most substances can exist as gases if heated or at low pressure, though some require extremely high temperatures. For example, metals vaporize only under very hot conditions.

Q: Why is gas useful in everyday life?
A: Gases are used for fuel, in cooking, heating, scientific research, and industrial processes. They are also essential for life — oxygen for breathing and carbon dioxide for plant growth.

Q: What toxic gases can be found in nature?
A: Methan, Carbon Monoxide (CO), Hydrogen Sulfide (H₂S), Nitrogen Dioxide (NO₂), Nitric Oxide (NO), Sulfur Dioxide (SO₂), Radon (Rn).

Are all gases dangerous to humans?
In general, almost all gases in large quantities and in their pure form are dangerous to humans. What we breathe and call air is a mixture of oxygen and other gases.

Can the average person detect toxic gases?
Yes, but relying solely on your senses is extremely dangerous, as the most deadly gases are often odorless or paralyze the sense of smell.

Which dangerous gases can be identified by smell, and what does the smell resemble?
Hydrogen sulfide (like rotten eggs), Natural gas (similar to rotten cabbage/sulfur), Ammonia (a strong smell of ammonia), Sulfur dioxide (the smell of a burning match or sulfur), Chlorine (a strong, suffocating smell of bleach). Second warning: do not attempt to identify gases by smell; it can be very dangerous.

• Did you know that helium is lighter than air, which is why balloons float?
• Air is actually a mixture of gases, mostly nitrogen (78%) and oxygen (21%), with tiny amounts of other gases.
• The “smell” of household gas is not natural; an odorant is added to detect leaks.
• Carbon dioxide is what gives soda its fizz.
• Plasma, often called the fourth state of matter, is a super-hot gas with electrically charged particles, found in lightning, neon signs, and the sun!
• Compressed gases can be dangerous if not handled carefully — even a small leak under pressure can cause accidents.

A gas is a state of matter. Many chemical substances can exist in a gaseous state.