Materials 4.1.1Define atom (160) The smallest part of an element that can exist chemically.Define molecule (165) Two or more atoms that are normallybonded together covalently.(outer electrons of some atoms come closeenough to over lap and are shared betweennuclei, thus forming a ‘covalent bond’). (see4.5.1)
Materials 4.1.1Define alloy (159) A mixture that contains at least onemetal. This can be a mixture of metals ora mixture of metals and non metals.Define composite (160) A mixture composed of two or moresubstances (materials) with onesubstance acting as the matrix (glue).
Materials 4.1.2Describe a bond as a force of attractionbetween atoms.
Materials 4.1.2Three types of bonding. 1. Ionic (it is a bond formed by the attraction between two oppositely charged ions). 2. Covalent (4.5.1) page 61 3. Metallic. (4.4.1) page 60
Materials 4.1.3Describe how materials are classified intogroups according to similarities in theirmicrostructures and properties. Wood: Hardwood – Softwood – Manufactured board. Metal: Ferrous – Non ferrous – Alloys Plastics: Thermoplastic – Thermoset – Elastomer.
Materials 4.1.3 Ceramics: Glass – Clay Composites: See later on.We classify all these materials by what theylook like under the microscope.They can also be listed according to theirproperties. SEE LATER ON.
Materials 4.1.4Explain that several classifications arerecognized but that no single classificationis perfect. We recognise that materials havesimilarities so we group them together. But sometimes this ‘crude’ grouping of materials from various groups is simply only a convenient method.
Materials 4.1.5Describe that, for this course materials areclassified into groups: timber, metals,plastics, ceramics, food and composites:and that some of these groups havesubdivisions.