William O. answered • 04/10/19
Eccentric STEM/Testing Tutor With a Flair for Helpful Anecdotes
First, in order to find the answer to this question, we have to know how wide a Carbon atom is from one side to the other. Unfortunately, this is no easy task, and sources are difficult to track down for the general "atomic radius", which is a poorly defined term for any of five different ways of measuring an atom from end to end. As such, unless you have been given guidance on how to find the atomic radius, I will use the most easily available number from WolframAlpha (courtesy of WebElements). The number given is 70 pm, or 70 picometers (aka 70 trillionths of a meter, or 7*10^-11 m). If the pencil lead is 0.10 mm wide (1*10^-4 m), then all we need to do is divide the two to find out how many of one can fit into the other: (1.0*10^-4)/(7.0*10^-11)=1428571, but we only have 2 significant figures from the measurement of the pencil lead, so we shorten our answer to 1400000 atoms.
