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States of Matter

We are taught in middle school that there are three states of matter: Solids, Liquids and Gases. Things are not always that are not so simple, but that’s where we will start.




Here is the microscopic behavior of atoms in liquid argon, and molecules in liquid bromine, and water.

Microscopic view of liquid argon Microscopic view of liquid bromine Microscopic view of liquid water
Microscopic view of the atoms in liquid argon. Microscopic view of the Br2 molecules in liquid bromine. Microscopic view of the H2O molecules in liquid water.



Bromine gas and liquid



Microscopic view of atoms of an element (gas phase). Microscopic view of molecules of an element (gas phase).
Microscopic view of the atoms of the element argon (gas phase). Microscopic view of the molecules of the element nitrogen (gas phase).

Note that an element:

  • consists of only one kind of atom,
  • cannot be broken down into a simpler type of matter by either physical or chemical means, and
  • can exist as either atoms (e.g. argon) or molecules (e.g., nitrogen).

A molecule consists of two or more atoms of the same element, or different elements, that are chemically bound together. Note that the two nitrogen atoms which comprise a nitrogen molecule move as a unit.


Microscopic view of molecules of a compound (gas phase).
Microscopic view of the molecules of the compound water (gas phase). Oxygen atoms are red and hydrogen atoms are white.


Microscopic view of a mixture of two elements and a compound (gas phase).
Microscopic view of a gaseous mixture containing two elements (argon and nitrogen) and a compound (water).



Gases, liquids and solids are all made up of microscopic particles, but the behaviors of these particles differ in the three phases.

Microscopic view of a gas Microscopic view of a liquid. Microscopic view of a solid.
Microscopic view of a gas. Microscopic view of a liquid. Microscopic view of a solid.



A solution is a homogeneous mixture of one or more solutes dissolved in a solvent.

Solvent: the substance in which a solute dissolves to produce a homogeneous mixture

Solute: the substance that dissolves in a solvent to produce a homogeneous mixture
Note that the solvent is the substance that is present in the greatest amount.

Many different kinds of solutions exist. For example, a solute can be a gas, a liquid or a solid. Solvents can also be gases, liquids or solids.

Microscopic behavior of several different kinds of solutions. Note that in each case, the solute particles are uniformly distributed among the solvent particles.

Microscopic view of bromine gas dissolved in Ar gas Microscopic view of argon gas dissolved in liquid water
Microscopic view of Br2 gas (solute) dissolved in Ar gas (solvent). Microscopic view of Ar gas (solute) dissolved in liquid H2O (solvent).
Microscopic view of liquid bromine dissolved in liquid water Microscopic view of solid NaCl dissolved in liquid water
Microscopic view of Br2liquid (solute) dissolved in liquid H2O (solvent). Microscopic view of solid NaCl (solute) dissolved in liquid H2O (solvent). Note that the ionic solid, NaCl, produces Na+ ions (blue) and Cl ions (green) when dissolved in water.


Microscopic view of solid krypton dissolved in solid xenon
Microscopic view of solid Kr (solute, blue) dissolved in solid Xe (solvent, red).


Phase transitions






boiling versus evaporation: similar but not the same

Sublimation of ice, over a few days

of dry ice



Multiple simultaneous phase changes

A small piece of rapidly melting solid argon simultaneously shows the transitions from solid to liquid and liquid to gas. (Wikipedia, Phase transition)

Phase transitions inside a super tall building


The Nasa Vehicle Assembly Building sometimes has its own rainclouds.



Brownian motion

“Brownian motion is named after Robert Brown – a botanist in the 1800’s, who looked at a bit of pollen on a microscope slide. He saw that the pollen, suspended in water, moved about.

This moving about is what we know as Brownian Motion. The pollen particle (in our GIF it is the big white blob) is bombarded by water molecules (the yellow dots), which then makes the pollen particle move about.”


Is everything a solid, liquid or gas?


Consider Play-Doh – that’s somewhere between a solid and a liquid. (If you think that it’s a solid, try pushing some. Not a solid!)

Play-Doh is mostly flour, salt and water, so it’s basically just (unleavened) dough. There are a lot of extra components like colourings, fragrances, preservatives etc, but these are present at low levels and don’t have a huge effect on the rheology.

The trouble with saying it’s basically “just” dough is that the rheology of dough is fearsomely complicated. In a simple flour/salt/water dough you have a liquid phase made up of an aqueous solution of polymers like gluten, and solid particles of starch. So a dough is basically a suspension of solid particles in a viscous fluid…

At low stresses, dough behaves like a solid because the flocculated particles act like a skeleton. However the bonds between flocculated particles are weak (they’re only Van der Waals forces) so at even moderate stresses the dough flows and behaves like a liquid. Dough, and Play-Doh, are best described as non-Newtonian fluids.

– John Rennie

How does play-doh work


“Oobleck is a fancy name for cornstarch in water, but it is one of the clearest examples of a non-Newtonian fluid. Cornstarch is a polysaccharide consisting of linked glucose molecules. When suspended in water, these molecules produce a matrix that resists rapid movement, but can flow past each other when moved more slowly.”

“Thus, Oobleck feels solid when you hit it, but flows when you caresse it. The vibrations in this GIF are keeping the Oobleck moving, so it’s acting as a solid and bouncing about, then reverts back to a liquid state.”


Silly Putty

Mark Rovetta writes “Silly Putty is quite dramatic (for putty) and often used as a teaching-aid to demonstrate a rheid – a now somewhat obsolete term for a material that exhibits a wide range of mechanical behavior depending upon the magnitude of stress.”

“Silly Putty fractures if hit with a hammer, bounces like rubber, stretches like metal, and can flow through a hole like a fluid.”





Over a period of minutes or hours,  rocks obviously are solids. Just hold one and try to bend it. Over a period of days or months they also appear to be solids.

But now consider a statue carved out of solid rock that is a thousand years old – sometimes, with careful examination, you might notice a tiny change in shape – how is that tiny change possible? Nonetheless, yup, we still call rock a “solid”.

But now consider rock that is being put under pressure for millions of years – it flows and bends!

Over long periods of time, rocks are not solids, then, they are rheids /ˈriːɪd/ – A non-molten solid that deforms by viscous flow at least a thousand times faster than it would deform elastically under the same applied stress. (Wikipedia)




Molecular Workbench: Apps and animations

Physics: Mechanics, Fluid Mechanics and Dynamics, Electromagnetism, Quantum
Chemistry: Thermodynamics, States of Matter, Chemical bonds, Water and solution, Reactions
Biology, Biotechnology, Nanotechnology,


Bose-Einstein condensates

Bose-Einstein Condensation is a form of matter at the coldest temperatures in the universe…



The Coolest Gas in Universe Scientific American 12 2000 Graham Collins


Plasma (from Greek πλάσμα, “anything formed”) has properties unlike those of the other states. It is a mixture of + electrically charged ions, and – free electrons.

– – – –
from http://www.chem4kids.com/files/matter_plasma.html:

Man-made plasmas are everywhere. Think about fluorescent light bulbs – inside the long tube is a gas. Electricity flows through the tube when the light is turned on. The electricity acts as an energy source and charges up the gas. This charging and exciting of the atoms creates glowing plasma inside the bulb. The electricity helps to strip the gas molecules of their electrons.

Neon signs are glass tubes filled with gas. When the light is turned on, the electricity flows through the tube. The electricity charges the gas and creates plasma inside of the tube. The plasma glows a special color depending on what kind of gas is inside.

Inert gases are usually used in signs to create different colors. Noble gases such as helium (He), Neon (Ne), Argon (Ar), and Xenon (Xe) are all used in signs.

Stars are big balls of plasma at really high temperatures. The high temperatures break apart atoms and so create plasma.

The temperature of plasmas can be very different. Fluorescent lights are cold compared to really hot stars. However, they are still both forms of plasma, even with the different physical characteristics.

– – –

How is plasma like gas?

It does not have a definite shape or a definite volume, unless enclosed in a container.

How is plasma different from gas?

It is easily affected by electric fields and by magnetic fields.

“Under the influence of a magnetic field, it may form structures such as filaments, beams and double layers. Plasma is the most abundant form of ordinary matter in the Universe, most of which is in the rarefied intergalactic regions, particularly the intracluster medium, and in stars, including the Sun.” (Wikipedia)

– – –
Lightning BBC africa thunerstorm plasma


Plasma ball


Non-classical states of matter:

Crystals with some degree of disorder
Liquid crystal states
Magnetically ordered
Quantum spin liquid
Glass is a special type of solid





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