Nanoparticles C
Aperçu
Photographs of lifeguards from forty years ago show a white stripe painted across the nose. The cream that made the stripe was zinc oxide, and it worked: nothing gets past it. Walk into a pharmacy today and you can buy a sunblock that contains the same zinc oxide, at a similar strength, that goes on completely clear. No new element was discovered to achieve that, and the formula on the tube is still ZnO. The one thing the manufacturer changed was how large the pieces of solid are.
That is the whole surprise of this topic. Chop a familiar substance small enough and it stops behaving the way the textbook says it should. It may melt at a lower temperature, catalyse a reaction it used to ignore, change colour, or lose its colour altogether. This lesson explains where the cut-off lies, gives you the piece of arithmetic that predicts the change before you ever see the substance, and then asks the question that governments are still arguing over: if a material behaves like a different substance at this size, is it safe to assume the old safety data still applies to it?
Objectifs
- Nanoscience refers to structures that are 1-100 nm in size, of the order of a few hundred atoms. Nanoparticles show properties different from those for the same materials in bulk and have a high surface area to volume ratio, which may lead to the development of new computers, new catalysts, new coatings, highly selective sensors, stronger and lighter construction materials, and new cosmetics such as suntan creams and deodorants. Students should know what is meant by nanoscience and nanoparticles and should consider some of the applications of these materials, but do not need to know specific examples or properties. Questions may be set on information that is provided about these materials and relating their use to their structure.
Carte mentale
Ce theme est schematise pour montrer comment les idees se relient.
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Note de cours
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Évaluation de la leçon
Félicitations, vous avez terminé la leçon sur Nanoparticles C. Maintenant que vous avez exploré le concepts et idées clés, il est temps de mettre vos connaissances à lépreuve. Cette section propose une variété de pratiques des questions conçues pour renforcer votre compréhension et vous aider à évaluer votre compréhension de la matière.
Vous rencontrerez un mélange de types de questions, y compris des questions à choix multiple, des questions à réponse courte et des questions de rédaction. Chaque question est soigneusement conçue pour évaluer différents aspects de vos connaissances et de vos compétences en pensée critique.
Utilisez cette section d'évaluation comme une occasion de renforcer votre compréhension du sujet et d'identifier les domaines où vous pourriez avoir besoin d'étudier davantage. Ne soyez pas découragé par les défis que vous rencontrez ; considérez-les plutôt comme des opportunités de croissance et d'amélioration.
- Nanoscience refers to structures with sizes in the range: A. 0.1 nm to 1 nm B. 1 nm to 100 nm C. 100 nm to 1000 nm D. 1000 nm to 10 000 nm Answer: B
- What is 1 nanometre expressed in metres? A. 1 x 10^-3 m B. 1 x 10^-6 m C. 1 x 10^-9 m D. 1 x 10^-12 m Answer: C
- A cube of a solid has edges of length 4 nm. What is its surface area to volume ratio? A. 0.67 nm^-1 B. 1.5 nm^-1 C. 96 nm^-1 D. 384 nm^-1 Answer: B
- A given mass of a metal is a better catalyst when it is supplied as nanoparticles rather than as a single lump. This is because the nanoparticles have: A. a larger volume B. a lower density C. a higher surface area to volume ratio D. a different chemical formula Answer: C
- Which statement about a nanoparticle of zinc oxide is correct? A. It has a different chemical formula from bulk zinc oxide. B. It has the same formula as bulk zinc oxide but may show different properties. C. It has the same properties as bulk zinc oxide in every respect. D. It is a single molecule of zinc oxide. Answer: B
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