# 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?