# Problem: Very small semiconductor crystals composed of approximately 1000 to 100,000 atoms, are called quantum dots. Quantum dots made of the semiconductor CdSe are now being used in electronic reader and tablet displays because they emit light efficiently and in multiple colors depending on dot size. The density of CdSe is 5.82 g/cm3.If you wanted to make one 6.5-nm dot from multiple 2.5-nm dots, how many 2.5-nm dots would you need?

###### FREE Expert Solution

Assuming 1 dot is a perfect sphere:

$\overline{)\mathbf{V}\mathbf{=}\frac{\mathbf{4}}{\mathbf{3}}{\mathbf{\pi r}}^{\mathbf{3}}}$

• Calculate the volume of a 6.5-nm dot

d = 6.5 nm
r = d/2 = 6.5/2 = 3.25 nm → convert to cm

r = 3.25x10-7 cm

V = 1.4379x10-19 cm3

Calculate the mass of a 2.5 nm dot

mass 6.5-nm dot = 8.4x10-19 g

• Calculate the volume of a 2.5-nm dot

d = 2.5 nm
r = d/2 = 2.5/2 = 1.25 nm → convert to cm

###### Problem Details

Very small semiconductor crystals composed of approximately 1000 to 100,000 atoms, are called quantum dots. Quantum dots made of the semiconductor CdSe are now being used in electronic reader and tablet displays because they emit light efficiently and in multiple colors depending on dot size. The density of CdSe is 5.82 g/cm3.

If you wanted to make one 6.5-nm dot from multiple 2.5-nm dots, how many 2.5-nm dots would you need?

What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Density concept. You can view video lessons to learn Density. Or if you need more Density practice, you can also practice Density practice problems.