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My 9 year old wants to know if a single atom exists in a certain state of matter — or must it be associated with other atoms in order to define a state?

Asked by: Julianne from Pennsylvania

A single, isolated atom would not be considered to be in any particular state (or “phase”) of matter; it must indeed be associated with other atoms for the idea of a state of matter to be meaningful.

The four primary phases of matter and the names for transitions between the different phases

Classical physics recognizes three states of matter. In a solid, the molecules (or atoms) that make up the material are connected by chemical bonds, and are more or less fixed in place, although they may vibrate a bit about their fixed positions. In a liquid, the molecules are still connected to each other, but sort of tumble over each other and have some freedom to move throughout the material; they are not fixed in place. In a gas, the molecules are no longer bound to each other, but are free to move through space, only occasionally bumping into each other.

Typically, the transition from one state of matter to another is accomplished through heat transfer. Adding heat energy to a solid loosens the atomic bonds enough to allow the molecules to begin tumbling around each other, forming a liquid; the addition of more energy allows molecules to escape from the surface of the liquid, forming a gas.

If we add even more energy to a gas, some of the molecules in the gas may begin to lose electrons when they collide with each other at high speed; we then get a combination of gas, positively charged ions, and electrons that is sometimes called the fourth state of matter, a plasma. A lightning bolt is an example of matter in the plasma state.

Some exotic variations of these states of matter are possible under special conditions: superfluids, ferrofluids, supersolids, Bose condensates, etc. Each have unusual properties of their own. These exotic forms of matter are being actively studied by physicists today.

Answered by:

David G. Simpson, PhD
Research Physicist
NASA Goddard Space Flight Center