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Which of the following statements could not be used to describe nanoparticles?
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(A) Particles one to 100 nanometers in size.
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(B) Particles that are smaller than most atoms.
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(C) Particles with a high surface-area-to-volume ratio.
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(D) Particles with different properties than those of the same material in bulk.
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(E) Particles containing a few hundred atoms or ions.
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We are asked which statement does not describe nanoparticles.
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Let’s start by discussing what a nanoparticle is.
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Nanoparticles are particles of matter that are between one and 100 nanometers in diameter.
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These are very small particles indeed.
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A nanosized particle could fit into a box 100 by 100 by 100 nanometers.
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Answer option (A) does correctly describe nanoparticles, and so we can rule it out.
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Nanoparticles come in a variety of shapes, including cubic structures called nanocubes, spherical nanospheres, and even nanotubes.
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These tiny structures usually contain a few hundred atoms or ions.
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And so we can rule out answer option (E) as the statement does describe nanoparticles.
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We can immediately see that answer option (B), particles that are smaller than most atoms, does not make sense.
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If nanoparticles consist of several hundred atoms or ions, then they cannot be smaller than most atoms.
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The statement does not describe nanoparticles.
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To be sure, let’s rule out answer options (C) and (D) as well.
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For any object, such as particles, we can calculate a surface area as to volume ratio.
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Small particles will have a large ratio, and large particles, a small ratio.
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Let’s clear some space to prove this.
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If we compare small particle one by one by one with a big particle 10 by 10 by 10, the volume of the small particle is one times one times one, and for the big particle 10 times 10 times 10, which gives one unit cubed for the small particle and 1000 units cubed for the big particle.
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The surface area of the small particle will be six, because there are six sides, multiplied by the area of one side, which is one times one, which gives six units squared.
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In a similar way, the surface area of the large particle is six multiplied by 10 times 10, which is 600 units squared.
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For each particle, we can now put these values into a ratio.
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And if we remove the units for simplicity, for the small particle, we get six as to one, and for the large particle, 600 as to 1000.
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If we simplify the ratio for the large particle, we get 0.6 as to one.
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Can you see that the small particle has a large ratio and the bigger particle has a smaller ratio?
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We can rule out answer option (C), particles with a high surface-area-to-volume ratio, as this statement does describe these tiny nanoparticles.
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Nanoparticles are a hot topic in science.
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Because of their tiny size and very high surface-area-to-volume ratio, they have very different properties than a bulk piece of the same material.
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This is the reason why nanoparticles interest scientists so much.
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We can rule out answer option (D) as this statement does correctly describe nanoparticles.
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Finally, which statement could not be used to describe nanoparticles?
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The answer is (B) particles that are smaller than most atoms.