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

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

exactly my thought, how to calculate that?!

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!!!!

mfb
Mentor
You can draw an equilateral triangle in the lattice.

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

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

mfb
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.

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

mfb
Mentor

i don't know to how to draw this, using what program?

mfb
Mentor
Every drawing program can draw lines. Windows always comes with Paint, for example.

pffffft i've been thinking about this problem for far too long i'm at my wits end, i really need to stop wasting my time with this and study, i feel nervous already cause i wasted so much time, plz give me a more strong hint, save me some time, thank you

solved it