Question

The radius of an atom of gold (Au) is about 1.35 Å.

Answer 1

Answer : The number of gold atoms will be, $3.52\times 10^7$

Explanation :

First we have to determine the diameter of an atom of gold.

$Diameter=2\times Radius$

Given :

Radius of an atom of gold = $1.35\AA$

$Diameter=2\times 1.35\AA=2.7\AA$

Conversion used : $(1\AA=10^{-7}mm)$

$Diameter=2.7\AA=2.7\times 10^{-7}mm$

Now we have to calculate the number of gold atoms.

$\text{Number of gold atoms}=\frac{\text{Span length}}{\text{Diameter of an atom of gold}}$

$\text{Number of gold atoms}=\frac{9.5mm}{2.7\times 10^{-7}mm}=3.52\times 10^7$

Therefore, the number of gold atoms will be $3.52\times 10^7$

Answer 2

Two radius of an atom is equal to the diameter. Adding up all the diameter of  the atoms, it should be equal to 9.5 mm. Therefore, we simply convert the units to the same units then divide 1.35 A to 9.5 mm. We calculate as follows:

no. of atoms = 0.0095 m / 1.35x10^-9 m = 7037037 atoms 

Hope this answers the question. Have a nice day.