WEBVTT 00:00:00.500 --> 00:00:03.976 Welcome to GCSE Edexcel Science revision. 00:00:04.126 --> 00:00:09.715 Unit S C 26: Bulk and surface properties of matter including nanoparticles. 00:00:12.367 --> 00:00:21.667 Bulk properties describe a material on an everyday scale, such as density, stiffness, strength, hardness, electrical conductivity and thermal conductivity. 00:00:21.817 --> 00:00:28.066 Read the property and its units carefully; hardness is resistance to scratching, not the same as toughness. 00:00:30.733 --> 00:00:35.651 Glass ceramics are often hard, heat-resistant and chemically resistant, but brittle. 00:00:35.801 --> 00:00:41.463 Transparent glass suits windows; changing composition and treatment changes its properties. 00:00:44.133 --> 00:00:47.747 Clay ceramics are made by shaping clay and heating it strongly. 00:00:47.897 --> 00:00:56.228 Their hardness, heat resistance and durability suit bricks, tiles and pottery, but brittleness limits uses where impacts or bending are common. 00:00:58.900 --> 00:01:04.776 Polymers are often low-density and good electrical insulators; they can be flexible or rigid. 00:01:04.926 --> 00:01:09.449 Heat resistance and mechanical behaviour vary widely between polymers. 00:01:12.100 --> 00:01:16.538 Metals generally conduct heat and electricity and can often be shaped. 00:01:16.688 --> 00:01:23.065 Their density, strength, melting point and corrosion resistance vary; alloys can alter their suitability. 00:01:25.733 --> 00:01:29.699 A composite combines different materials to use their properties together. 00:01:29.849 --> 00:01:34.402 In fibreglass, glass fibres strengthen a surrounding polymer (the matrix). 00:01:34.552 --> 00:01:38.081 Carbon-fibre composites can be strong while having a low mass. 00:01:38.231 --> 00:01:43.723 The surrounding matrix transfers loads between fibres; fibre direction affects properties. 00:01:48.400 --> 00:01:54.414 Concrete contains stones and sand (aggregate) held together by a cement-based material (matrix). 00:01:54.564 --> 00:01:58.938 It is strong when squeezed (in compression), but weaker when pulled (in tension). 00:01:59.088 --> 00:02:02.435 Steel reinforcement helps it resist pulling forces. 00:02:02.585 --> 00:02:06.280 The composite’s properties depend on how its parts work together. 00:02:08.933 --> 00:02:17.621 Choose materials for the intended load, temperature, electrical requirements, environment, lifetime, manufacturing method, cost and disposal. 00:02:17.771 --> 00:02:22.699 Data should support the choice; no material category is best for every product. 00:02:25.367 --> 00:02:30.529 Nanoparticles have dimensions on the scale of about 1, 100 nanometres. 00:02:30.679 --> 00:02:39.520 One nanometre is ten to the power minus 9 metres; typical atoms are smaller, while many molecules have sizes that overlap the lower nanoscale. 00:02:42.200 --> 00:02:46.605 A nanoparticle contains many atoms and is not just a single atom. 00:02:46.755 --> 00:02:54.189 Compare actual size data rather than treating all atoms, molecules and nanoparticles as having one fixed size. 00:02:56.867 --> 00:03:01.044 As particles become smaller, surface area per unit volume increases. 00:03:01.194 --> 00:03:03.285 For a cube of side length L, 00:03:03.435 --> 00:03:06.677 surface area equals six times side length squared, 00:03:06.827 --> 00:03:13.098 volume equals side length cubed and surface-area-to-volume ratio equals six divided by side length, 00:03:13.248 --> 00:03:15.104 with inverse-length units. 00:03:15.254 --> 00:03:20.767 Halving cube size doubles its surface-area-to-volume ratio; use consistent length units. 00:03:25.433 --> 00:03:33.399 Splitting a fixed volume into smaller particles increases its total exposed surface without changing the total material volume, 00:03:33.549 --> 00:03:37.647 if the particles remain separate and their surfaces are accessible. 00:03:40.300 --> 00:03:45.142 Nanoparticles have a larger proportion of their atoms at or near the surface. 00:03:45.292 --> 00:03:54.731 This can make a substance behave differently from a large sample of the same material (the bulk material), for example in its reactions or how it interacts with light. 00:03:57.400 --> 00:04:04.768 Nanoparticle catalysts have a large surface area for their mass, so less material may be needed for the same catalytic effect. 00:04:04.918 --> 00:04:10.953 If particles clump together (aggregate), less of their surface is exposed and the benefit may be reduced. 00:04:13.633 --> 00:04:19.168 Nanoparticles of titanium dioxide or zinc oxide can be used in sunscreens. 00:04:19.318 --> 00:04:27.423 They help protect against ultraviolet radiation while looking less white on skin than some formulations containing larger particles. 00:04:30.100 --> 00:04:34.857 Other examples include catalytic surfaces and antimicrobial coatings. 00:04:35.007 --> 00:04:43.080 Effectiveness depends on the material, size, coating and exposure conditions; a nanoscale label alone does not guarantee a benefit. 00:04:45.733 --> 00:04:52.729 Some nanoparticles may enter the body by inhalation, ingestion or skin exposure and may interact with cells. 00:04:52.879 --> 00:05:00.557 Risk depends on exposure, material and form; do not assume that every nanoparticle is either harmless or equally dangerous. 00:05:03.233 --> 00:05:09.994 Small particles can reach sites larger particles may not, and their large surface area can increase interactions. 00:05:10.144 --> 00:05:16.061 Potential effects on organisms and environmental persistence need evidence for each material. 00:05:18.733 --> 00:05:26.421 Evaluate benefits against possible health and environmental risks, using measured exposure and toxicity data where available. 00:05:26.571 --> 00:05:32.661 Lack of evidence of harm is not the same as proof of safety; uncertain data should limit conclusions. 00:05:35.333 --> 00:05:42.478 For a material choice, compare both bulk performance and surface effects, and consider manufacturing, use and disposal. 00:05:42.628 --> 00:05:47.928 Safe handling may require avoiding dust and following the product or laboratory controls. 00:05:50.600 --> 00:05:55.107 That completes Bulk and surface properties of matter including nanoparticles. 00:05:55.257 --> 00:05:58.603 Revisit the notes and test yourself on the revision website.