In a liquid, the particles are more loosely packed than in a solid and are able to flow around each other, giving the liquid an indefinite shape. Solids also have a high density, meaning that the particles are tightly packed together. Solids have a definite shape, as well as mass and volume, and do not conform to the shape of the container in which they are placed. Because of this, particles in a solid have very low kinetic energy. The electrons of each atom are constantly in motion, so the atoms have a small vibration, but they are fixed in their position. © Keith S.In a solid, particles are packed tightly together so they don't move much. Please use the search box to find pages / postings on specific themes.ĬhemTeach: an email list for chemistry teachers So it is questionable whether we should describe the particles being further apart in a liquid, rather than just taking up a little more space. These fields interact with the fields of other quanticles around them (that is, they form 'bonds' – such as dipole-dipole interactions), so in condensed phases (solids and liquids) there are really discrete particles with gaps between them. Therefore, these quantiles do not actually have definite volumes, in the way a marble or snooker ball has a clear surface and a definite volume. Rather these 'particles' (or quanticles) are fuzzy blobs of fields where the field intensity drops off gradually, and there is no surface as such. * A difficulty for teachers is that the entities being discussed as 'particles', often molecules, are not like familiar particles that have a definitive volume, and a clear surface. Not only do a range of ideas have to be coordinated, but these involve directly observable phenomena (floating), and abstract concepts (such as density), and conjectured nonobservable submicroscopic/nanoscopic level entities. Perhaps this is not surprising when we consider what the explanation would involve: Coordinating concepts to understand the implication of ice floating That is, he may have had the necessary elements of knowledge to appreciate that as ice floats, the particles in ice were not closer together than they were in water, but had not coordinated these discrete components to from an integrated conceptual framework. As the number of water molecules has not changed, then the smaller volume means the particles are on average taking up less space: that is, they seem to be closer together in the water, not further apart*.īill was no doubt aware that ice floats in water, but if Bill appreciated the relationship of mass and volume (i.e., density) and how relative density determines whether floatation occurs, he does not seem to have related this to his account here. If the density of some water is higher than that of the ice from which it was produced on melting then (as the mass will not have changed) the volume must have decreased. The partial disruption of the hydrogen bonds in the solid that occurs on melting allows water molecules to be, on average, closer* in the liquid phase at 0˚C.Īs ice float in water, it must have a lower density.

Indeed it is not so for water – so ice floats in cold water. This misrepresents the modest difference generally found in practice – as can be appreciated from the observations that volume increases on melting are usually modest.Īlthough generally the particles in a liquid are considered further apart than in the corresponding solid*, this need not always be so. Often figures in basic school texts show much greater spacing between the particles in a liquid than in the solid phase of the same material. This is generally true* when comparing the same substance, but this is something that tends to be exaggerated in the basic teaching model often used in school science. It just moves.īill reports that the particles in liquids are 'further apart, than the ones in … solids'. Yeah, and you said that liquids contain particles? Did you say they move, what did you say about the particles in liquids?Įr, they're quite, they're further apart, than the ones in erm solids, so they erm, they try and take the shape, they move away, but the volume of the water doesn't change. So if I put those two things together, that tells me that ice should contain particles? So, you said that solids contain particles, This point was followed up later in the interview. Well, solids they stay same shape and their particles only move a tiny bit. So how do you know if something is a solid, a liquid or a gas? Well there's three groups, solids, liquids and gases.

Bill introduced the idea of particles when talking about what he had learn about the states of matter. Bill, a Y7 student, explained what he had learnt about particles in solids, liquids and gases. Bill was a participant in the Understanding Science Project.

Liquid particles