The diameter of a rubidium atom is 4.94 Ã…. We will consider two different ways of placing the atoms on a surface. In arrangement A, all the atoms are lined up with one another to form a square grid. Arrangement B is called a close-packed arrangement because the atoms sit in the "depressions" formed by the previous row of atoms:

(a) Using arrangement A, how many Rb atoms could be placed on a square surface that is 1.0 cm on a side?
(b) How many Rb atoms could be placed on a square surface that is 1.0 cm on a side, using arrangement B?
(c) By what factor has the number of atoms on the surface increased in going to arrangement B from arrangement A? If extended to three dimensions, which arrangement would lead to a greater density for Rb metal?

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(a) (b)