Chemistry
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Properties of matter. (2022). In Q-files Encyclopedia, Science, Chemistry. Retrieved from
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"Properties of matter." Science, Chemistry, Q-files Encyclopedia, 25 Oct. 2022.
https://www.q-files.com/science/chemistry/properties-of-matter.
Accessed 19 Mar. 2024.
Properties of matter 2022. Science, Chemistry. Retrieved 19 March 2024, from
https://www.q-files.com/science/chemistry/properties-of-matter
Science, Chemistry, s.v. "Properties of matter," accessed March 19, 2024.
https://www.q-files.com/science/chemistry/properties-of-matter
Properties of matter
Matter exists as a solid, a liquid or a gas. It is made up of atoms of certain types (elements), either of just one type or a combination of two or more. Different materials have differing degrees of density (the amount of matter packed into a certain volume), strength, elasticity (stretchiness) and plasticity (the extent to which its shape can be changed). Other properties include: how well it conducts heat and electricity, whether it is soluble or not and what its boiling and melting points are.
Intermolecular forces
In any liquid or solid, forces are needed to hold neighbouring molecules together. These forces both attract and repel other molecules. Without attractive forces, the molecules would not come together to form liquids or solids; the molecules would drift apart freely and everything would be gas. But without repulsive forces all matter would squash closer and closer together into an incredibly dense point. So, for any material, a combination of push-pull forces are at work between its molecules. These are called intermolecular forces. Many properties of solids and liquid depend on them.
At the molecular scale, in which distances are measured in nanometres (a nanometre is a thousand millionth of a metre), attractive forces work at relatively large distances, while repulsive forces apply at close quarters.
Properties of liquids
A liquid's molecules are attracted to each other, but the attraction is not so great as in solids; a liquid's molecules can move around much more and are constantly vibrating. The liquid can thus change shape and flow, although, like solids, it still takes up the same volume. Liquids cannot be stretched or cut into pieces in the way that some solids can.
A liquid's molecules also cannot be squeezed together, meaning that when a liquid flows through a confined space such as a pipe, it pushes against the wall of the container. In other words, it exerts pressure.
Surface tension
Within a liquid, the attractive forces between its molecules pull in all directions. But at the surface, its molecules are pulled more towards the body of the liquid than in the opposite direction, the air above. The liquid's surface molecules are thus bound together in a force called surface tension. It is as if the liquid has a stretchy skin on its surface. This "skin" enables some insects, such as water striders, to move about on the surface of water, for example.
In a drop of liquid, the forces pull the surface all round towards the centre. The "skin" effect holds the liquid together in a spherical shape. This may distort (creating a "teardrop") as gravity pulls it downwards.
Viscosity
Some liquids can flow more easily than others. Viscosity is the term used to describe this property. Water, for example, flows more easily than oil, because it has low viscosity. Its molecules are sliding over one another more easily than those of oil. Normally, a liquid's viscosity decreases with a rise in temperature: warm honey flows more easily than cold honey.
Properties of solids
In many solid substances, the atoms or molecules are arranged in a regular pattern known as a crystalline framework. These crystals are not irregular lumps but orderly, geometric shapes with sharp edges and flat sides at certain angles to each other. Solids that are not crystalline are called amorphous: they have no regular pattern in their molecules. Glass is an example.
Crystalline structures can be broken up by, for example, heating, which makes the atoms vibrate more until the forces holding the atoms together are overcome (the solid then melts), or by stress, which causes the layers of atoms to shift out of position, a process known as dislocation. Dislocations can happen slowly over time: this is known as creep failure. In metals, it can eventually result in sudden breakage, a change known as fatigue.
Stress and strain
When a material is stretched, the distances between its atoms increase slightly. The force applied to stretch the material is proportional to the distance the material stretched when the force was applied. This is called Hooke's Law.
Stress makes layers of atoms in a substance or crystal slide over one another. By adding atoms of another kind to it, a substance's atoms can be anchored together more effectively. This is what happens in metal alloys. Atoms of other metallic elements added to iron turn into steel, a much stronger material. An alloy is harder than the two or more metals of which it is composed. Steel cables in a suspension bridge do not break when they are pulled downwards by the force exerted by the weight of the deck.
Elasticity
If a wire is suspended from a firm support with a weight hung at the other end, the force acting on the wire causes its length to increase slightly. If the weight is not too great, the wire will return to it original length when the load is removed. The degree of elasticity that material has depends on the strength of its intermolecular forces.
Plasticity
There is a limit to a material's elasticity. If that limit is exceeded, the material will not return to its original shape after the load is removed. Its layers of atoms will have slid permanently over each other into new positions. This property of changing shape permanently after stress is applied is called plasticity. Materials such as dough and clay are highly plastic at room temperature. Others, such as most metals, become plastic on heating.
If a metal such as copper can be stretched out into a fine wire without breaking, then it is described as ductile. Large increases in length may be possible before a ductile material snaps. Some materials can be beaten into different shapes without breaking, as when for example, a metal such as gold is flattened out into thin sheets called gold leaf. This property is known as malleability.
Some materials, such as glass, fracture almost immediately: they have no elasticity. This property is known as brittleness. Other materials become brittle on heating: clay, for example, when baked in a kiln.
Conductivity
Many metals have a pure crystalline structure. Their atoms' electrons are bound loosely and can drift easily from atom to atom: this is why metals conduct electricity and heat so easily. Materials such as plastics, glass and wood do not have these free-flowing electrons on their atoms so they are poor conductors. They do, however, serve as good insulators of both electricity and heat, which is why plastic, for example, is used to cover wires in an electric cable or in handles for saucepans in the kitchen.
Consultant: Nina Notman