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# If I have a chart that claims that the Atomic radius of Rubidium is 248 picometers cubed, how can I calculate how many Rubidium atoms span the length of 1.00 centimeter (Assume that the Rubidium atoms are touching each other) ?

##2.02 * 10^(7)"atoms of Rb"##

For starters, the atomic radius of rubidium cannot be expressed in picometers cubed, ##"pm"^3##, because that is a unit used for **volume**, not for **length**.

My guess would be that you're indeed dealing with the atomic radius of rubidium, which is equal to ##"248 pm"##.

If that's the case, the first thing to do here would be to convert the desired length, i.e. ##1.00## centimeters, to picometers. To do that, go from centimeters to meters first, then from meters to picometers

##1.00 color(red)(cancel(color(black)("cm"))) * (1color(red)(cancel(color(black)("m"))))/(10^2color(red)(cancel(color(black)("cm")))) * (10^(12)"pm")/(1color(red)(cancel(color(black)("m")))) = 1.00 * 10^(10)"pm"##

So, you know that the **radius** of a rubidium atom is equal to ##"248 pm"##. The thing to look out for here is the fact that you need to use the **diameter** of an atom, which is you know is equal to

##color(purple)(bar(ul(|color(white)(a/a)color(black)("diameter" = 2 xx "radius")color(white)(a/a)|)))##

The diameter of a rubidium atom will thus be

##"diamter" = 2 xx "248 pm" = "496 pm"##

Now all you have to do is figure out how many atoms would fit in that length

##1.00 * 10^(10)color(red)(cancel(color(black)("pm"))) * "1 Rb atom"/(496color(red)(cancel(color(black)("pm")))) = color(green)(bar(ul(|color(white)(a/a)color(black)(2.02 * 10^7"atoms of Rb")color(white)(a/a)|)))##

The answer is rounded to three .