The molecules are held closely together in a regular pattern called a lattice. If the ice is heated, the energy of the molecules increases. This means that some of the water molecules are able to overcome the intermolecular forces that are holding them close together, and the molecules move further apart, forming liquid water.
This is why liquid water is able to flow: the molecules have greater freedom to move than they had in the solid lattice. If the molecules are heated further, the liquid water will become water vapor, which is a gas. The attractive forces between the particles are very weak given the large distances between them.
Changes in phase : A change in phase may occur when the energy of the particles is changed. The kinetic theory of matter is also illustrated by the process of diffusion. Diffusion is the movement of particles from a high concentration to a low concentration. Liquid — In a liquid, particles will flow or glide over one another, but stay toward the bottom of the container. The attractive forces between particles are strong enough to hold a specific volume but not strong enough to keep the molecules sliding over each other.
Gas — In a gas, particles are in continual straight-line motion. The kinetic energy of the molecule is greater than the attractive force between them, thus they are much farther apart and move freely of each other.
In most cases, there are essentially no attractive forces between particles. Solids also have a definite volume; that is, they keep their size no matter how you try to change them. Solids are divided into two main categories, crystalline solids and amorphous solids, based on how the particles are arranged. Crystalline solids, or crystals, are regarded as "true solids. Common table salt is one example of this kind of solid. In crystalline solids, the atoms, ions or molecules are arranged in an ordered and symmetrical pattern that is repeated over the entire crystal.
The smallest repeating structure of a solid is called a unit cell, which is like a brick in a wall. Unit cells combine to form a network called a crystal lattice.
There are 14 types of lattices, called Bravais lattices named after Auguste Bravais, a 19th-century French physicist , and they are classified into seven crystal systems based on the arrangement of the atoms. The ChemWiki page at the University of California, Davis lists these systems as cubic, hexagonal, tetragonal, rhombohedral, orthorhombic, monoclinic and triclinic.
Aside from the regular arrangement of particles, crystalline solids have several other characteristic properties.
They are generally incompressible, meaning they cannot be compressed into smaller shapes. Because of the repeating geometric structure of the crystal, all the bonds between the particles have equal strength. This means that a crystalline solid will have a distinct melting point, because applying heat will break all the bonds at the same time. Crystalline solids also exhibit anisotropy.
This means that properties such as refractive index how much light bends when passing through the substance , conductivity how well it conducts electricity and tensile strength the force required to break it apart will vary depending on the direction from which a force is applied.
These "more energetic particles" may have sufficient energy to escape from the surface of the liquid as gas or vapour. This process is called evaporation and the result of evaporation is commonly observed when puddles or clothes dry. Evaporation takes place at room temperature which is often well below the boiling point of the liquid. Evaporation happens from the surface of the liquid. As the temperature increases the rate of evaporation increases. Evaporation is also assisted by windy conditions which help to remove the vapour particles from the liquid so that more escape.
Evaporation is a complex idea for children for a number of reasons. The process involves the apparent disappearance of a liquid which makes the process difficult for them to understand. It is not easy to see the water particles in the air. Also, evaporation occurs in a number of quite differing situations - such as from a puddle or bowl of water where the amount of liquid obviously changes, to situations where the liquid is less obvious - such as clothes drying or even those where there is no obvious liquid at all to start with - such as bread drying out.
A further complication is that evaporation may be of a solvent from a solution e. These situations are quite different yet all involve evaporation. Evaporation may also involve liquids other than water e. The particle model can be used to explain how it is possible to detect smells some distance away from the source.
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