# How many Rb atoms to fit on a 9Cm^2 square?

UnD3R0aTh
1. The problem is in the attachments

2. Basic chemistry knowledge

3. The radius of one Rb atom is 4.95/2 time 10^-8 cm, we calculate the area then divide 9 into the area of one atom, we get the number of atoms, why is 4.7 x 10^15 atoms wrong?

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Mentor
There are empty spaces between the atoms - they need more space than just pi*r2.

UnD3R0aTh
exactly my thought, how to calculate that?!

UnD3R0aTh
excellent, i solved the first one, but the second one i'm not really sure how to calculate the side of the triangle that's enclosing one atom!!!!

Mentor
You can draw an equilateral triangle in the lattice.

UnD3R0aTh
yes but it looks like it's side is longer than the diameter, how to calculate it's length?!

UnD3R0aTh
no wait, the triangles do not work, they overlap! parallelograms work! how to calculate the area of a parallelogram using it's sides?

Mentor
Then you are drawing the wrong triangles. Use the centers of the atoms, this is easier. Afterwards, find out how many atoms per triangle (or triangles per atom) you have.

UnD3R0aTh
can u plz draw a diagram like u did with the first one?

Mentor