Solid, liquid and gaseous matter in this hot springSolid, liquid and gaseous matter in this hot spring Everything is made of matter. Every object, substance, chemical and material is matter. This includes not only things you can see easily, but also specks of dust too small to notice, houses and cars, living things like trees and your own body, the rocks of the Earth, the clouds in the sky and the invisible air around you. And not only objects and substances on Earth are made of matter. All of the planets and stars in deep space contain matter. In fact everything in the entire Universe is made of matter. All matter is made of tiny building blocks called atoms.

The emptiness of space?The emptiness of space?


There are places where there is no matter. If there is no matter then there is nothing at all. The total or complete absence of matter is called a vacuum. However a total vacuum is very unusual. “Space” is named because it is supposed to be just empty space, with no matter. But even in the depths of space, a few micro-particles of dust or some wispy bits of gas are floating about. These tiny bits of matter may be several metres apart, instead of crammed together like they are on Earth. But they are still present. Here on Earth, powerful vacuum pumps can suck most of the matter out of a container, but never quite all of it.

Water as a solid (ice), liquid and gas (water vapour)Water as a solid (ice), liquid and gas (water vapour)

States of matter

Matter exists in three main forms, called the states of matter. These are solid, liquid and gas. In a solid such as ice, the molecules (its atoms, bonded together) are very close together and joined in a rigid pattern. They can hardly move. So a solid object stays the same volume and does not change its shape. In a liquid such as water, the molecules are still quite close together but they are not joined to each other. They can move about, which means the whole liquid can change shape and flow, although, like the solid, it still takes up the same volume. In a gas like water vapour, the molecules can move nearer together or farther apart. So a gas can also get bigger or smaller, to fill the container it is in.

Changing states

A diagram of the water cycleA diagram of the water cycleMatter or substance can change state from solid to liquid, or liquid to gas. This usually happens by adding heat. Matter can also change state the other way from gas to liquid or liquid to solid. This usually happens by cooling (taking away heat). A common example which is all around us is water. The world’s water is always on the move and changing state in a never-ending process, the water cycle.


Colourful liquids of different densitiesColourful liquids of different densities

Properties of matter

Matter has several properties. One of the main properties is its state—solid, liquid or gas. Another is the type of atoms it is made of. A third property of matter is density. This is the amount of matter in a certain place or volume. The more matter within a certain volume, the denser the substance or object and the greater its mass. The densities of solids, liquids and gases are given a density value relative to water, which is 1. Oil is a little less dense than water (0.9), while air, like all gases, is much less dense (0.0012). The densest substance on Earth is the metal osmium (22).

A galaxy clusterA galaxy cluster

Dark matter

Scientists think that a large part of the total mass of the Universe—about 84% of it—cannot be accounted for by just the mass of objects we can see or detect. They call this mysterious "invisible" portion of the Universe dark matter. Dark matter cannot be detected using telescopes, because it does not give out light or any other electro-magnetic radiation. Instead, we know it is there because of the gravitational effect it has on visible matter; for example, the speeds at which galaxies rotate seem to be affected by an invisible force. It is likely that dark matter is made up of types of subatomic particle that have yet to be discovered.

 Dave Hawksett

See also in Science

See also in Space

See also in Earth

Scientists sometimes describe a fourth state of matter, called plasma. This is like a gas in which a number of its atoms or molecules have been ionized—given an electrical charge. This usually occurs at high temperatures.

In crystalline solids, or crystals, the atoms and molecules are packed together in a regular, repeating pattern.

Solids can change directly into gases. This process is called sublimation.

The highest temperature at which a liquid can exist without becoming a gas is called its critical temperature.

The volume of a substance in its liquid form is usually greater than in its solid form—but that is not the case with water.

Does glass really "flow" like a liquid? The "evidence" for this is that glass in old windows is sometimes found to be thicker at the bottom than at the top. This is, however, a myth: once it becomes a solid, glass never flows.

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