Chemistry Moles?

Question

If it were possible to make a continuous circular ring of tin atoms one row of atoms wide, what would be the approximate mass of this piece of jewelry assuming the width of the average human finger is 1 cm? The atomic radius of a single tin atom is 158 pm and the density of tin is 7.26 g/cm3

Answer 1

If the human finger is 1 cm wide and assumed to be a cylinder, it has a circumference of pi cm, or approximately 0.0314 m. If the atomic radius of a tin atom is 158 pm, then it has a diameter of 158 x 10^-12 m. It therefore takes (0.0314 / 158 x 10^-12) = 198,734,177 tin atoms to complete the ring. The atomic mass of tin is 118.710. The mass of the ring is therefore (198734177 / 6.023 x 10^23)*118.710 = 3.9 x 10^-14 g, or 0.039 pg. I didn't use the bulk density of tin.

Note that the number of atoms in the ring is so large that I neglected the fact that they are arrayed in a 200 million-gon instead of a straight line. Also, remember that a mole (6.023 x 10^23) of atoms of a given element has a mass in grams equal to the atomic mass.