Anything you see around you, that takes up space and has mass (volume), is matter. Examples are a table, chair, tree, plants, animals and even the air we breathe. They are all forms of matter.
Matter is made of atoms that come in different types, or elements. These elements range from hydrogen, being the lightest, through to uranium and beyond. Each element consists of different numbers of atoms – tiny particles or molecules that are in constant motion. When they bond together in larger numbers they form a type of mass, becoming visible to the naked eye, taking the form of objects around us that we all take for granted. You cannot see them individually but the different atoms combine to form an enormous variety of compounds from simple water to complex proteins. It is just like dropping a grain of salt on the floor. You would have great difficulty finding it, if you were looking for it. But drop a cupful of salt and it would be easy to see because it would have spilt everywhere! That is the same with atoms. Alone they might not be significant but together they become powerful visible matter.
Each atom consists of protons and neutrons. Protons carry a positive charge while neutrons have no charge at all. Protons and neutrons are each called nucleons since they are found in the nucleus, and they are orbited by negatively charged particles called electrons. The way nucleons are arranged at any time is what causes matter to differ in texture, shape, size, colour, odour, volume, mass, weight, density and motion (known as their physical properties). The physical properties of matter usually remain constant, like fire is always hot and water is always liquid, though their chemical properties can change.
The Changes and Phases of Matter
Every form of matter is driven by energy. Through this energy matter can actually change from one state to another, called a “physical change”. Physical changes usually occur when energy is either added to it, or taken away, but it does not change the chemical nature of matter. It involves a change only in the physical properties. For example, a carpenter can always change the physical property of a piece of wood by crafting it into something else like a piece of furniture. But, even though the wood has changed shape in its physical properties, the chemical nature of the wood has not been altered. A chemical property denotes how an object changes into a new substance. For example, the wood the carpenter used has a chemical property called flammability (it can easily burn) and despite being turned into a chair or table, when sparks are added to this new piece of furniture, it can still burn.
Matter can be broken down into six types, of which the three most common are: solids (like fruits), liquids (like drinks) and gases (like oxygen). Each of the types relate to each other in how they change chemically, from one phase to another. Melting, freezing, condensation and evaporation are examples of phase changes. Most substances can exist in different phases and changes in a phase are also physical changes. For example, water can exist in the solid, liquid or gas phase. Melting occurs when a solid changes to a liquid, freezing occurs when a liquid becomes a solid, evaporation involves a liquid becoming a gas and condensation involves a gas becoming a liquid. Phase changes require either the addition of heat energy (melting, evaporation) or the subtraction of heat (condensation, freezing). Changing the amount of heat energy usually causes a temperature change.
The stages of a phase change can be summarised as follows: The molecules (particles) of a solid matter vibrate around a fixed position. This restriction gives the solid its definite volume and shape. As energy in the form of heat is added to a solid, its molecules begin to vibrate more rapidly until they break out of their fixed positions and the solid becomes a liquid. This is called melting and occurs at a definite temperature known as the melting point. The molecules of a liquid can actually move throughout the liquid but are held in place by their own forces. This accounts for the liquid having a definite volume but no definite shape. As more heat is added and a specific temperature is reached, the molecules throughout the liquid are energised enough to escape. Bubbles of vapor then form and rise to the surface, escaping into the surrounding space in the form of evaporation. The change of liquid to a vapour or gas occurs at boiling point. The molecules of a gas are free to move in every possible way which explains why gas has neither a definite shape or volume, but usually expands to fill any container in which it is placed.
In 1968 scientists discovered that the atom, as small as it was, actually contained even smaller particles called quarks that are held together by other particles called gluons. They are increasingly regarded as the actual building blocks of matter instead of the atom.
Sources
http://www.dmturner.org/Teacher/Library/5thText/ChemPart1.htm
http://209.85.229.132/search?q=cache:0bWnd0vdIoIJ:www.visuallearningco.com/guides/Matter/WhatisMatter.pdf
http://209.85.229.132/search?q=cache:yHpxed8Tp40J:vega.org.uk/downloads/what_is_matter_129.ppt
