1) In a solid, particles are closely packed together and can only vibrate, giving solids a definite shape and volume. Crystalline solids have particles packed in a regularly repeating pattern. 2) Liquids conform to the shape of their container but have a nearly constant volume. They are mobile with intermolecular forces still important. 3) Gases fill their entire container, have very weak or no bonds between molecules, and their molecules can move freely.

1. Solid
A crystalline solid:atomic resolution image of strontium titanate. Brighter atoms are Sr and darker onesare Ti.
Main article: Solid
In a solid,the particles (ions,atoms,or molecules) are closely packed together. The forces between particles are
strong so that the particles cannotmove freely but can only vibrate. As a result, a solid has a stable,definiteshape,
and a definite volume. Solids can only changetheir shapeby force, as when broken or cut.
In crystallinesolids,the particles (atoms,molecules,or ions) arepacked in a regularly ordered, repeating pattern.
There are various different crystal structures,and the samesubstancecan have more than one structure (or solid
phase). For example, iron has a body-centred cubic structureat temperatures below 912 °C, and a face-centred
cubicstructurebetween 912 and 1394 °C. Ice has fifteen known crystal structures,or fifteen solid phases,which
existat various temperatures and pressures.[2]
Glasses and other non-crystalline,amorphous solids withoutlong-rangeorder are not thermal equilibriumground
states; therefore they are described below as nonclassical states of matter.
Solids can betransformed into liquidsby melting, and liquids can betransformed into solidsby freezing. Solids can
also changedirectly into gases through the process of sublimation,and gases can likewisechangedirectly into
solids through deposition.
Liquid
Structure of a classical monatomic liquid. Atoms have manynearest neighbors incontact, yet no long-range order is present.
Main article: Liquid
A liquid isa nearly incompressible fluid thatconforms to the shapeof its container but retains a (nearly) constant
volume independent of pressure.The volume is definiteif the temperature and pressureare constant. When a
solid is heated above its melting point, itbecomes liquid,given that the pressureis higher than the triplepoint of
the substance.Intermolecular (or interatomic or interionic) forces arestill important,but the molecules have
enough energy to move relativeto each other and the structureis mobile. This means that the shapeof a liquid is
not definitebut is determined by its container.The volume is usually greater than that of the correspondingsolid,
the best known exception being water, H2O. The highesttemperature at which a given liquid can existis its critical
temperature.[3]
Gas
The spacesbetweengas molecules are verybig. Gas molecules have veryweakor no bonds at all. The molecules in"gas" can
move freelyandfast.
Main article: Gas
A gas is a compressiblefluid.Not only will a gas conformto the shapeof its container but it will also expand to fill
the container.
In a gas,the molecules have enough kinetic energy so that the effect of intermolecular forces is small (or zero for
an ideal gas),and the typical distancebetween neighboring molecules is much greater than the molecular size.A
gas has no definite shapeor volume, but occupies the entire container in which it is confined.A liquid may be
converted to a gas by heating at constantpressureto the boilingpoint,or elseby reducing the pressureat
constanttemperature.
At temperatures below its critical temperature, a gas is also called a vapor,and can be liquefied by compression
alonewithout cooling.A vapor can existin equilibriumwith a liquid (or solid),in which casethegas pressure
equals the vapor pressureof the liquid (or solid).
A supercritical fluid (SCF) is a gas whose temperature and pressureareabove the critical temperature and critical
pressurerespectively. In this state, the distinction between liquid and gas disappears.A supercritical fluid has the
physical properties of a gas, but its high density confers solventproperties in some cases,which leads to useful
applications.For example, supercritical carbon dioxideis used to extract caffeinein the manufacture
of decaffeinated coffee.[